Physiology of development of schoolchildren: educational manual 9786010450981

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AL-FARABI KAZAKH NATIONAL UNIVERSITY

G. Tussupbekova

PHYSIOLOGY OF DEVELOPMENT OF SCHOOLCHILDREN Educational manual

Almaty «Qazaq University» 2020

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UDC 612(075) LBC 28.707 я73 T 96 Recommended for publication by the decision of the Faculty of Biology and Biotechnology, RICO of the Kazakh National University named after Al-Farabi (protocol №1 dated 13.11.2019) Reviewers: Doctor of Medical Sciences, Professor A.M. Aykimbaev Doctor of Biological Sciences, Professor M.K. Murzakhmetova

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Tussupbekova G. Physiology of development of schoolchildren: educational manual / G. Tussupbekova. – Almaty: Qazaq University, 2020. – 158 p. ISBN 978-601-04-5098-1 The educational manual considers in detail consistent patterns of individual development, basic methods of diagnostics of physiological levels of development of children and adolescents, structure, functioning and age of the transformation of regulatory systems (nervous and endocrine), sensory and visceral systems, physiological characteristics of the body in different periods of ontogenesis. The course physiology of development of schoolchildren is of a great practical importance and is one of the most important components of pedagogical education. Physiological knowledge is necessary for the teacher to actively and consciously participate in the health protection of children and adolescents. The educational manual is recommended for students of pedagogical and psychological-pedagogical directions, it can also be useful for teachers, practical psychologists and social workers.

UDC 612(075) LBC 28.707 я73 ISBN 978-601-04-5098-1

© Tussupbekova G., 2020 © Al-Farabi KazNU, 2020

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PREFACE

Physiology of development of schoolchildren is one of the rapidly developing Sciences of modern biology. Among many biological Sciences, an important place is occupied by age physiology, which is the basis of studying intrauterine and postnatal development of the body, as well as studying the mechanisms and factors that affect the body in different periods of human life. The course of age physiology is of a great practical importance and is one of the most important components of pedagogical education. Elucidation of the laws of development of the child, specifics of physiological system functioning at different stages of ontogenesis and the mechanisms defining this specificity is a necessary condition of ensuring normal physical and mental development of younger generation. The relevance of the course of physiology of development of schoolchildren is caused by the need for a systematic study of the human life cycle: from fertilization of the egg to deep aging, taking into account the peculiarities of the regulation of homeostasis in ontogenesis. This relevance is due to the increasing requirements for the proper organization of the work of the teacher to ensure the harmonious development and improvement of the functionality of the body of children and adolescents. The main questions that should arise in the future teachers and psychologists in the process of education and training of the child at school – what it is, what are its features, where it will be most effective. To answer these questions is not easy, because it requires deep knowledge about the child, the laws of the development, age and individual characteristics. This knowledge is extremely important for the development of psycho-physiological foundations of the organization of educational work, the development of the child's adaptation mechanisms, affected by the impact of innovative technologies.

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The main purpose of the study of the physiology of the development of students is the formation in the future teachers of the knowledge about the age characteristics of the developing organism, knowledge of the laws underlying the preservation and strengthening of the health of students, maintaining their high performance in various types of training and employment. The teacher's deep knowledge of the laws of the development of the body of a growing person, his arming with the necessary initial information and skills in the field of age-related anatomy, physiology and hygiene is one of the basic conditions for meeting the high demands to the training of future teachers. The structure of the proposed textbook is designed so that students have a clear idea of the laws of the body in the process of ontogenesis, the features of each age stage. At the end of each Chapter, there are questions for independent work of students, which allow refreshing the knowledge of the main provisions of the studied material that require a special attention.

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CHAPTER

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PATTERNS OF GROWTH AND DEVELOPMENT OF THE BODY Age physiology is the science of the vital activity of an organism and its individual parts (cells, tissues, organs, functional systems) in the age aspect. The object of study is the human body at various stages of its individual development. The age physiology considers the functional processes of the human body in different periods of life. Age physiology is an independent branch of human physiology, the subject of which is the study of the laws of formation and development of the body's physiological functions throughout its life course from fertilization to the end of life. In dependence of the age period, the age physiology is distinguished as follows: age neurophysiology, age endocrinology, age physiology of muscular activity and motor function; age physiology of metabolic processes, cardiovascular and respiratory systems, systems of digestion and excretion, physiology of embryonic development, physiology of infants, physiology of children and adolescents, physiology of mature age, gerontology (science of aging). The main tasks of studying age physiology are the following: – The study of the functioning of various organs, systems and the organism as a whole; – Identification of exogenous and endogenous factors that determine the characteristics of the functioning of the body at different age periods; – Definition of objective criteria for age (age standards); the establishment of patterns of individual development. 5

Age physiology is closely connected with many branches of physiological science and makes extensive use of the data from many other biological sciences. So, to understand the laws of formation of functions in the process of individual human development, the data from physiological sciences such as cell physiology, comparative and evolutionary physiology, physiology of individual organs and systems: heart, liver, kidney, blood, respiration, nervous system, etc., are required. At the same time, the laws and regularities discovered by age physiology are based on the data from various biological sciences: embryology, genetics, anatomy, cytology, histology, biophysics, biochemistry, etc. Finally, the age data of physiology, in turn, can be used to develop various scientific disciplines. For example, age physiology is important for the development of pediatrics, pediatric traumatology and surgery, anthropology and gerontology, hygiene, developmental psychology and pedagogy. Patterns of growth and development of the organism. Ontogenesis (the individual development of the organism) is a set of transformations that the body undergoes from the birth to the end of life. The German biologist E. Haeckel (1866) introduced this term. In ontogeny, there are two relatively independent stages of development: prenatal and postnatal. The first begins from the moment of conception and continues until the birth of the child, the second from the moment of birth to the death of the person. The first stage lasts in average for 280 days. The duration of the second stage for all people is different and it identifies the following periods of development: early, mature and final (period of aging). For workers of physical culture of a particular interest is the period of ontogenesis, when the body undergoes the most intensive physical development and the formation of the human psyche, when the body is most sensitive to the means of physical education. This is the period from the birth to 18-20 years. The growth and development of the body of children and adolescents. Growth is an increase in the length, volume and body weight of children and adolescents. The growth occurs due to the processes of hyperplasia – an increase in the number of cells and the number of constituent organic molecules and due to hypertrophy – an increase in the cell size. 6

Processes of hyperplasia occur most intensively during fetal development and less intensively after birth. In the postnatal period, some cells lose their ability to divide. Thus, the formation of new muscle cells is possible only during the first 4 months after birth. A further increase in the mass and volume of muscle tissue occurs mainly due to the formation of a huge number of nerve processes and synaptic contacts. Development is qualitative changes, which consist in the complication of the structure and functions of all tissues and organs and the processes of their regulation. The growth and development of the body occur unevenly – as a heterochronous process. In the non-simultaneity of the growth and development of individual systems, biological expediency is observed. First, vital organs develop, providing adaptation to specific environmental conditions and survival of the organism. The Russian physiologist P. Anakin put this concept of accelerated and selective development of individual structures forward. Thus, the fetal brain intensively develops at the 2nd-10th weeks of pregnancy; the heart – at the 3d-7th, the digestive organs – at the 11th-12th weeks. If the selectivity of development is impaired, then the fetus is not viable. Uneven growth and development is observed after birth. Therefore, by the time when the baby is born, the muscles of the lips, tongue, and cheeks are relatively well developed, ensuring the sucking process. The child's body performs gas exchange processes with the external environment, thermoregulation processes, and the cardiovascular system functions as well. At the same time, the muscles of the body are poorly developed; the child is unable to keep his head upright for the first months. Functionally not mature are many areas of the cerebral cortex. A little time passes and the nervous system begins to develop at high rates, the mass of the brain increases, the possibility of forming conditioned reflexes increases, and so on. After 5 years, the nervous system develops and the other system switches until the body reaches certain functional maturity. Based on the uneven growth rate and development of the organism, the entire stage of achieving functional maturity is conventionnally divided into several age periods. There are various age periodization schemes, but when raising children and adolescents, it is advisable to use the scheme proposed at the International Symposium on Age Physiology in 1965. 7

In the individual human development, there are two periods of intrauterine and extra uterine development. During the prenatal period, the formation of organs and body parts characteristic of man occurs. This period is divided into the embryonic phase (first 8 weeks), when the initial development of the embryo and organs takes place, and the fetal phase (3-9 months), during which further development of the fetus occurs. The uterine period is the period when a new individual continues its development outside the mother's body. It lasts from the moment of birth to death. After birth, the extra uterine period of a person's life is divided by age, taking into account morphological and functional features: 1. Newborn 1 – 10 days; 2. Infancy – 10 days – 1 year; 3. Early childhood – 1-3 years; 4. First childhood – 4-7 years; 5. Second childhood – 8-12 years for boys, 8-11 years for girls; 6. Adolescence – 13-16 years for boys, 12-15 years for girls; 7. Adolescence – 17-21 years for boys, 16-20 years for girls; 8. Mature age (1 period) – 22-35 years for males, 21-35 years for females; 9. Mature age (2nd period) – 36-60 years for males, 36-55 years for females; 10. Old age – 61-74 for men, 56-74 for women; 11. Old age (2nd period) – 75-90 years for men and women; 12. Centenarians – 90 years or more. Features of the development of the organism in different periods. Morphological functional features characterize each age period. Thus, in a newborn child, the head is round, large (1/4 of the entire body length, in an adult – it is1/8) and its circumference is 34-36 cm. The neck and chest are short, the belly is long, the legs are short, and the arms are long. The muscles are poorly developed. The infancy is characterized by enhanced growth and development of organs and systems. During the year, the length of a child's body increases in average by 25 cm, and the weight reaches 10-11 kg. In the period of early childhood, growth slows down: the increase in mass and length of the body is much slower than in the first year. All the organs of the child in this period develop and strengthen the muscles and skeleton. 8

In the period of the first childhood, height growth prevails over weight gain. The growth of children of the 4th and 5th year of life slows down somewhat and is on average 4-6 cm per year; at the 6th and 7th year of life, the increase in growth is significant – up to 810 cm. This is the first period of stretching, which is associated with functional changes in the endocrine system. By the 5th year, the muscles develop significantly, especially on the legs, the muscles become stronger, their working capacity increases. In the period of the second childhood, growth in width again prevails, however, at this time, puberty begins, and by the end of the period body height increases, the rate of which is greater for girls. At the age of 10, the first differentiation occurs – the length and body weight of girls exceeds that of boys. The muscular system intensively develops, but in children of this age, the back muscles are still weak and cannot keep the body upright for a long time, which can lead to poor posture and curvature of the spine. The concentration of sex hormones is increasing, which provides the corresponding anatomical and physiological differences in the development of boys and girls. In adolescence, puberty occurs, accompanied by accelerated physical development. Conventionally, adolescence (in girls from 12 to 16 and in boys from 13 to 17 years old) is distinguished from youth (in girls from 16, in boys from 17 years). In physiological terms, adolescence is caused by an increase in the production of hormones, the main ones being growth hormone, sex hormones, thyroid hormones, and insulin. Puberty begins with the manifestation of secondary sexual characteristics, in girls it occurs about 2 years earlier than in boys. In parallel with puberty, there is an intensive growth of the body in length, the peak of its speed on average is 12 years and reaches 9 cm per year. In 15-16 years, there comes a gradual halt of growth. Boys have the highest growth rate at 14 years that reaches 10-12 cm per year. At 18-20 years, there is a gradual halt of growth. Both boys and girls, along with an increase in height, gain body weight, on average, up to 3-5 kg per year. In adolescents, all parts of the body, tissues and organs quickly grow and develop. Growth rates are not the same. The uneven growth of individual parts of the body causes a temporary incoordination of movements – clumsiness, awkwardness, and angularity appear. During this period, you need closely monitor the posture of a teenager. 9

Mature age is divided into two periods. The first period (in men – 22-35 years old, in women – 21-35 years old) is marked by the cessation of growth and the stability of functional items that achieve optimal development. The shape and structure of the body change little; there is a slight increase in the mass of the skeleton due to the deposition of new layers of bone substance on the surfaces of the bones. The maximum manifestation of most functions usually occurs at the age of 20-25 years, after which a gradual decrease in the intensity of their manifestation begins. At 20-25 years, there is an ideal for the person body weight. Usually stable body weight is kept up to 40-46 years. In the second period (for men – 36-60 years old, for women – 3655 years old), there is a gradual neuroendocrine restructuring, the function of the sex glands fades away (menopause). Climax is accompanied by significant changes in physiological functions (the concentration of hormones of the sex glands decreases in the blood, the functions of the thyroid gland, thymus, adrenal glands decrease). With the age, these primary changes lead to secondary ones: atrophy of the integument, lethargy, flabbiness, wrinkled skin, graying and loss of hair, reduction in the muscle volume and tone, limitation of mobility in the joints. The proportions of the body remain constant, but by the end of this period, they begin to decrease. Elderly and senile age are characterized by changes in the energy processes in the cell; decrease in the activity of respiratory enzymes. The regulation of the functions of organs and systems changes significantly. With age, the adaptive capabilities of the cardiovascular system change, which is reflected in a decrease in the heart rate at rest, in the elderly and senile people. Acceleration and retardation of development. Acceleration refers to the accelerated growth and development of children and adolescents, as well as the absolute increase in the size of the body of adults. E. Koch (1935) proposed this term. Acceleration was, noted when comparing anthropometric data obtained in the early 20s of the 20th century with data from the 30s of the 19th century, when they began to conduct anthropometric studies of children. Currently, epochal and intragroup acceleration is distinguished. Epochal acceleration refers to the acceleration of the physical development of modern children and adolescents in comparison with pre-

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vious generations. It manifests itself at the stage of intrauterine development. In modern newborns, body length is 0.7-1 cm longer, and weight is 60-100 g higher. As they grow, these differences increase. In modern children, reproductive functions are revealed earlier. There is the evidence of accelerated development of the cardiovascular, respiratory and motor systems. Intragroup acceleration is an accelerated physical development of children and adolescents in a certain age groups. Intragroup acceleration is characterized by higher growth, greater muscular strength and capabilities of the respiratory system. Such individuals develop puberty much faster and growth processes in them end earlier. Thus, intragroup acceleration is often combined with an increase in the physiological capabilities of the organism. However, individual acceleration is often accompanied by disharmonious development of various systems and functions, which leads to physiological disintegration and reduced functionality. In children with an increased development rate, endocrine disorders, chronic tonsillitis, nervous disorders, dental caries, and increased blood pressure are more common. After the 60-70s, the negative effects of acceleration began to appear. First of all, disproportionality of physical development, especially in the direction of the excess in body weight. The second negative phenomenon of acceleration is a decrease in lung capacity and a decrease in muscle strength. The reason for the disharmony of the physiccal development of modern children and adolescents is low physical activity. The biological mechanisms of acceleration are not yet clear. However, there is a number of hypotheses for the causes of acceleration; they can be divided into 3 main groups. The first group includes physicochemical hypotheses. E. Koch believed that modern children experience a more intense exposure to sunlight, which, in his opinion, is a growth stimulator. According to Tiber, the electromagnetic waves generated by the operation of numerous radio stations have a stimulating effect on the growth and development. D. Rudder associates acceleration with a possible change in the level of radiation. However, most researchers are inclined to accept the hypothesis of the stimulating effect of industrial waste. Industrial waste, being in the air environment, getting into the body with drin-

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king water, food in small doses, have mutagenic properties and therefore can have a bio stimulating heterocyst-like effect. The confirmation of this phenomenon may be the timing of registration of acceleration in different countries. Thus, acceleration was initially manifested in England, Norway, France (from 1830-1840), in Sweden, Denmark (from 1860), then in Russia, Japan, etc. The second group includes hypotheses explaining acceleration by changes in social conditions: improved nutrition (N. Lunch), medical care (M. Krivogorsky) and the influence of urban living conditions stimulating the pace of physical development. The third group is the hypothesis according to which acceleration is the result of cyclical biological changes of heterocyst and other phenomena. The heterocyst effect is associated with a widespread migration of the modern population and an increase in the number of mixed marriages. At the same time, the offspring of the first generation has a temporary advantage in physical development. It would be more correct to agree with the opinion of most authors who believe that the cause of acceleration lies in the complex influence of a number of factors, and that various factors play a leading role in different places and at different times. The analysis of the latest anthropometric measurements shows that acceleration is not a stage of progressive increase in the size of the human body, but represents only a phase in its development. Since the 70s of this century, in the most economically developed countries, for example, the USA, England, Sweden, the acceleration rate has slowed down or even stopped. Apparently, for the acceleration, the end of the XX and the beginning of the XXI century will be characterized by its complete stabilization, and then, possibly, by the beginning of the reverse process. Retardation is the process opposite to acceleration, a slowdown in physical development and the formation of functional systems of the body of children and adolescents. Biological mechanisms of retardation are poorly understood. At the present stage of the study, there are two main reasons for retardation. The first one is various hereditary, congenital and organic disorders acquired in postnatal ontogenesis; the second reason lies in various social factors. The adolescents with hereditary retarding factors, as a rule, by the time of the start of growth processes are not inferior in this indicator 12

to their peers; they simply reach these values 1-2 years later. The reason for the lag may be the diseases they suffered, but these lead to a temporary slowing down in the growth, and after recovery, the growth rates become higher, that is, the genetic program is implemented in a shorter period. The social factors have a significant negative impact. In most cases, it is the negative emotional microclimate surrounding the child in the family or in the children's institutions. Children brought up in the conditions of insufficient attention from parents and children brought up in orphanages and boarding schools are 1.52 years behind their peers in their development. Thus, retardation, regardless of the reasons for it, affects the rate of both physical and mental development. The human body as a whole. The structural unit of the human body, like in any living creature, is a cell. The basis of the vital activity of the organism is such important cell functions as metabolism, growth, development, movement, irritability, reproduction. In addition, the cell is the keeper of genetic information. Cells that are similar in structure have a common origin and perform the same function, combined in tissue. The tissues construct organs that form organ systems. The latter are integrated into the whole organism. The organism is a single whole and can exist only because of its integrity. The integrity of the organism is ensured by the neuron humoral regulation of its functions. The nervous system carries out nervous regulation. Biologically active substances are hormones that are contained in the blood, tissue fluid and lymph providing humoral regulation. The structure and chemical composition of cells. The main components of the cell are the nucleus, the cytoplasm, with organelles located in it, the cell membrane. About 90 elements of the Periodic Table of D.I. Mendeleev are found in the cells of living organisms. They are divided into three groups: macronutrients (oxygen, carbon, hydrogen, nitrogen, constituting 98% of the total cell content), microelements (magnesium, sodium, iron, potassium, calcium, sulfur, phosphorus, chlorine; they account for 1.9 %) and ultra-micro elements (zinc, copper, iodine, fluorine, bromine, gold, silver, aluminum, etc., their content is less than 0.1%). All these elements are part of the organic and inorganic substances of a living organism. Water and mineral salts represent inorganic substances in the cell. The water content in the 13

body varies from 40-95%, it is different in different tissues and depends on the physiological activity of the cell. Carbohydrates, fats and proteins represent organic matter. Classification and functions of tissues. According to their function, the tissues are divided into four groups: epithelial, connective, muscular and nervous ones. Connective tissues. The proper connective tissues are loose fibrous and dense fibrous, unformed and dense. In addition, there are tissues with special properties (reticular and fatty), solid skeletal (bone, cartilaginous) tissues, and liquid (blood and lymph) ones. Their main functions are protective, supporting, stocking. A special type of connective tissue is blood, whose intercellular substance is plasma, and the cellular components are red blood cells, white blood cells and platelets. Some connective tissues perform supporting and mechanical functions (dense fibrous tissue, cartilage, bone), other ones perform trophic, immune (phagocytosis and antibody production) functions (loose fibrous and reticular tissues, blood, lymph), as well as transport and respiratory functions (blood and lymph). Muscle tissue. The main property of muscle tissue is the ability to contract, which provided by contractile proteins (actin and myosin). There are striated and smooth muscle tissues. The striated muscle tissues form skeletal muscles. They consist of muscle fibers, whose length can range from a few millimeters to 10-12 cm. Each fiber contains a cytoplasm with numerous oval nuclei and myofibrils. In functional terms, they belong to arbitrary muscles, i.e., they contract according to the will of man. Smooth muscle tissue forms the musculature of internal organs (the walls of blood vessels, intestines, bronchi, bladder, ureters, etc.). These are spindle-shaped cells, in the cytoplasm of which there is one rod-shaped nucleus and myofibrils. Smooth muscles contract arbitrarily, they a characterized by long tonic contractions and relatively slow movements. After stretching, they keep their length for a long time. Nervous tissue. Thanks to nervous tissues, the perception of information entering the body and assurance of the reaction to it of the whole organism occurs. Its main properties are irritability (the ability to move from a state of rest to an active physiological state) and excitability (the ability to respond to irritation). These properties are 14

associated with the ability of the cells of the nervous, as well as muscular and glandular tissues to produce and transmit bioelectric potentials. The transmembrane potential difference that exists between the cytoplasm and the outer solution surrounding the cell is called the resting potential. Under the action of a stimulus, a rapid oscillation of the membrane potential arises – an action potential that occurs at the site of irritation. Distribution of action potentials along the nerve fibers provides information transfer in the nervous system. Special cells are neurons and neuroglia cells located between them that perform nourishing, supporting and protective functions for nervous tissue. The neuron consists of the body and the cytoplasmic processes (dendrites and axons). The transmission of a nerve impulse from one neuron to another is accomplished by means of intercellular contacts formed by the processes of neurons called synapses. The impulse arrives at the presynaptic terminal, which is limited by the presynaptic membrane and sensed by the postsynaptic membrane. Between the membranes there is the synaptic cleft. In the presynaptic ending, there are many bubbles containing mediators of physiologically active substances (adrenaline, acetylcholine, etc.). A nerve impulse entering a presynaptic terminal causes a release into the synaptic cleft of the mediator that acts on the postsynaptic membrane, causing the formation of a nerve impulse in the postsynaptic part. Epithelial tissues form the outer integuments of the body and line many cavities of the internal organs (mucous membrane of the internal organs, skin epithelium, and external and internal secretion glands). They perform protective, excretory and secretory functions. In them, the cells fit closely together, so there is very little intercellular substance. This structure of the tissues makes it difficult for microbes and harmful substances to enter the body. Often the cells of epithelial tissue are located in numerous layers, reliably protecting the organs located under them. The epithelial cells being exposed to harmful effects, in most cases die. In this regard, they are capable of rapid reproduction. A good example is the superficial cells of the skin: they gradually die off, exfoliate, and are replaced by new ones due to the multiplication of cells of a deeper layer. 15

Questions for self-control 1. What is ontogenesis? What periods does human ontogenesis include? 2. What is age periodization? What are the criteria for age periodization? 3. What are the features of the development of the child in the periods of early, first and second childhood? 4. What are the main physiological features of adolescence? 5. Describe the concepts "acceleration" and "retardation" of development.

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PHYSIOLOGY OF THE MUSCULOSKELETAL SYSTEM AND AGE FEATURES Functions of the musculoskeletal system. The musculoskeletal system unites the skeleton and the striated (skeletal) muscles and represents one of the most important systems of the human body. It performs a supporting and protective function and plays a crucial role in the movement. The skeleton consists of bones and the formations connecting them. In humans, over 200 bones make up to 18% of body weight in men and 16% in women. The proportion of muscles, respectively, accounts for 36% in men and 42% in women, and in male athletes, sometimes – up to 50%. In the human body, there are about 400 muscles. The skeleton has a supporting value, forming the structural basis of the body and determining its size and shape. The skeleton is also a passive organ of movement, as muscles are attached to it. In addition, the bones of the skeleton are a depot of salts of calcium, phosphorus and other elements that are involved in mineral metabolism. Many bones contain red bone marrow inside which blood cells are formed. Some parts of the skeleton (skull, chest, and pelvis) serve as a container and protection of vital organs is the brain, lungs, heart, etc. Muscles are an active part of the musculoskeletal system. The support function of the muscles is the protection of internal organs, which is carried out by the muscles surrounding the body cavities. Properties, composition and structure of bones. Bones have strength, resilience and lightness. The tissue that forms the bone is a 17

type of connective tissue. It is represented by bone cells and mineralized intercellular substance. Bone cells are of three types: osteocytes, osteoblasts and osteoclasts. Osteocytes are immured in the intercellular substance, are in contact with each other by the islets and provide for the metabolism in the tissue. Osteoblasts are located in the areas of bone formation and provide bone growth in thickness and its accretion at fracture. Osteoclasts (cell destroyers) are involved in bone desorption. The combined effect of all types of cells provides the restructuring of the bone with the growth and change in functional load. The mineral component of the bone is formed by calcium salts, which give the bones hardness. Organic substances (ossein, osseomucoid) provide the elasticity of bones. All bones, with the exception of their articulations, are covered with a periosteal. It is a thin connective tissue sheath, rich in nerves and vessels, penetrating into the bone through special openings. Through the periosteal, nutrition and innervation of the bone are carried out. Tendon ligaments and muscles are attached to the periosteal. On its inner surface there are osteoblasts. Under the periosteal there is a layer of compact substance, consisting of plates of bone tissue (trabecular) tightly lying with respect to each other. The layer of spongy substance, which contains loosely lying trabecular bone, is located deeper. Moreover, the plates of the spongy substance are in the directions of the greatest stretching and compression of the bones, and the compact substance prevails in the bones, which perform the function of support and movement. The shape of the bones may be long or short with a cavity inside (tubular), flat (wide), spongy and mixed. In the tubular bones, we distinguish the middle part – the diaphysis and the two ends – the epiphyses. A compact substance forms the diaphysis, and the epiphyses are spongy. Inside the diaphysis, there is a yellow bone marrow in the cavity, and in the cells of the spongy substance and in the flat bones there is a red bone marrow. The examples of flat bones are carpal bones, the example of mixed is vertebrae. There are two types of bone connections: continuous and discontinuous. Continuous connection pass through bone (pelvic bone), cartilage (vertebrae) and connective (most of the bones of the skull) tissue. Discontinuous ones are joints. The joint includes articular surfaces of articulated bones covered with cartilage, an articular capsule 18

surrounding the ends of bones and an articular cavity located between the bones inside the capsule. General overview of the human skeleton. In the human skeleton, there are three sections – the skeleton of the body, the skeleton of the limbs and the skeleton of the head. The skeleton of the body, or axial skeleton, is subdivided into the spine and chest skeleton. The spine skeleton is formed by 33–34 vertebrae located one above the other, between the units of which there are cartilage layers, giving it flexibility and elasticity. The spine consists of seven cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-5 coccygeal vertebrae. Each vertebra contains a body and an arc, from which seven processes extend (one spinouts, moving in the midline from the arc, 2 transverse, on the sides of the arc, 4 articular, extending up and down along the pair). Sacral vertebrae in adolescence grow together into one bone forming the sacrum. It has a triangular shape with the base facing up and the top down. Between the bodies and the arches of the vertebrae there are vertebral holes forming the spinal canal in which the spinal cord is located. The spinal column has four bends: the bulge directed forward is the cervical and lumbar lordosis and the two reversed bulges back form the thoracic and sacral kyphosis. The rib cage consists of 12 pairs of ribs, sternum and 12 thoracic vertebrae. In front of the sternum seven pairs of ribs, called true ribs are attached. The ends of 8-10 pairs with the help of cartilage are connected not with the sternum, but with the cartilage of the previous rib, these ribs are called false. The shortest ribs, 11-12 pair, are called oscillating. Their front ends are free. Skeleton of limbs. The skeleton of the limbs (upper and lower) can be divided into the skeleton of the free upper and lower extremities and the skeleton of the belt (shoulder, pelvic), which strengthens the limb on the body. The skeleton of the shoulder girdle consists of two paired bones – the scapula and the clavicle. The homers, the bones of the forearm (radial and ulnar) and the bones of the hand (wrists, metacarpus and phalanx of the fingers) form the skeleton of the free upper limb. The pelvic bone forms the skeleton of the pelvic girdle; it is comprised of 3 bones: the ilium, ischium, and pubis. At the site of their fusion on the pelvic bone, there is a groove is the acetabulum, which includes the head of the femur. The sciatic and pubic bones limit the 19

obdurate opening, tightened by the connective tissue membrane. The final fusion of the three bones occurs in girls at the age of 12-15, and in boys at the age of 13-16. The femur, the bones of the leg (large and small tibia) and the bones of the foot (tarsus and phalanges of the fingers) form the skeleton of the lower limb. The skeleton of the head, or skull, consists of the cerebral and facial regions. The brain area (skull) protects the brain from damage. Flat bones are fixedly connected to each other to form it: the front is unpaired frontal, the top is paired parietal, on the lateral sides, there is temporal and behind – unpaired occipital bone with a hole through which the brain and spinal cord are connected. The facial part of the skull includes the lower and upper jaws; the zygotic, nasal and other bones, which, in addition to the lower jaw, are fixedly connected to each other. The upper and lower jaws contain 16 cells each, in which the roots of the teeth are placed. Major muscle groups. Muscles are organs of the body of humans and animals, consisting of striated muscle tissue that can contract under the influence of nerve impulses. Each muscle is enclosed in connective tissue sheath having a smooth surface. When contracted, it moves relative to neighboring muscles with minimal friction. The fibers at the ends of the skeletal muscle gradually pass into the tendons. The tendon ends of the muscles are attached most often to different bones; only the mimic muscles an attached at one end to the skin. Usually, in the process of moving, not one, but a whole group of muscles is contracted. Muscles performing similar functions are called synergists, and the opposite ones are antagonists. Almost every muscle has its own antagonist (for example, flexors – extensors, etc.). The shape of the muscles may be long, short, wide and round. According to the functions performed in the body, muscles of the head, neck, chest, abdomen, back, and limbs are distinguished. The head muscles include the occipital, frontal, temporal, facial, chewing, and other muscles. The muscles of the neck include stern hyoid, sternocleidomastoid, and other muscles. External and internal intercostal, small and large pectoral, front and other muscles belong to the chest muscles. Straight, transverse, oblique, internal and external ones represent the abdominal muscles. They form the abdominals, which performs a 20

number of functions: participation in the act of breathing and movement of the spine, holding the abdominal organs in a normal position. The muscles of the upper limb are divided into the muscles of the shoulder girdle (deltoid muscle, etc.) and the free limb. The biceps muscle flexes the shoulder and forearm in the shoulder and elbow joints, and the triceps unbends them in the same joints. On the front surface of the forearm, there are the flexors of the hand and fingers; on the back – the extensors. The muscles of the lower limb form the pelvic girdle and the muscles of the free limb. The pelvic muscles include the lumbar and three gluteus, which provide flexion and extension in the hip joint, as well as maintaining the body in an upright position. The muscles that set the thigh and lower leg in motion are quadriceps and biceps. The feet and fingers are set in motion by a number of muscles, of which the largest is the gastrocnemius. It also takes part in keeping the body upright. Work and muscle fatigue. The work of muscles is associated with the ability of muscle tissue to contract and determined by the product of the mass of the lifted load and the height of the lift. Being relaxed the muscle does not work. Muscles require energy, the source of which is ATP, which is formed during glycolysis. Muscle work depends on the intensity of their blood supply. Glucose enters the muscles through the bloodstream and the products of its incomplete splitting are carried away. A prolonged muscle work leads to fatigue. Muscle fatigue is caused by the accumulation of lactic acid, carbon dioxide and other decomposition products. Fatigue is a normal physiological reaction of muscle tissues; it disappears after rest. For the first time, the fatigue mechanisms were studied by I. M. Sechenov in 1903. He found that the rate of fatigue was influenced by the rhythm of the work and the magnitude of the load. With an average rhythm of work and load, the highest performance and slow development of fatigue is noted. I. Sechenov showed that the restoration of working capacity of a tired right hand is faster, if during the rest period to work with the left hand. This phenomenon he called active rest. Uninteresting work causes fatigue faster than interesting one. Age features of the musculoskeletal system. During the individual's life, the skeletal system undergoes significant changes. 21

Therefore, the newborn has a large amount of cartilage tissue. During the first year of life, the bones grow slowly, from one to 7 years the growth accelerates. After 11 years, active growth begins again, and bone marrow cavities are formed. The chemical composition of bones in different periods of life varies. Inorganic substances (calcium salts) impart hardness to bones. In old age, their content increases, which makes bones more fragile than in other periods. Organic substances (ossein, osseomucoid) provide the elasticity of bones, the content of these substances is higher in childhood. This can lead to the curvature of the spine, and this is facilitated by the fact that in children the back muscles are weakly developed. A distinctive feature of the child's skull is the predominance of the size of the brain part over the facial one, which is associated with bone growth, teething and strengthening of the masticatory muscles. On the top of the skull of a newborn, the remains of a non-ossified connective tissue between the bones in the form of fontanels are preserved. There are six of them (front, rear, 2 wedge shaped and two mastoid). The largest one is the front, and the next is the rear. The anterior part is diamond is shaped, and ossifies by the age of 1.5 years. The posterior fontanel is located at the posterior end of the arrow and looks as suture and ossifies by 2 months. All the bones of the skull grow together by the age of 13. Individual facial features are formed during puberty. Due to the deposition of bone substance, with age, the bones of the facial skull become more massive. In adulthood, the ossification of the sutures of the skull begins. At an older age, these bones become thinner and lighter, and due to the loss of teeth and atrophy of the alveolar jaws, the face shortens and the lower jaw moves forward. In the newborn, the vertebral column is straight, with the exception of a small sacral curvature. The first bend of the spine, cervical lordosis, appears in a child in infancy, when he begins to hold the head. Thoracic kyphosis occurs at the age of 6 months. Lumbar lordosis and sacral kyphosis appear at the end of the first year of life. At first, the bends of the spine are not significant: the thoracic and cervical are finally formed, as a rule, by 6-7 years, the lumbar is by 12 years. The process of ossification of the upper extremities occurs unevenly at different age periods and lasts from 1 year up to 1822

20 years, and sometimes up to 25 years. In girls, the process of ossification ends 2 years earlier. At seven in children, the junction of the pelvic bones begins, which ends by the age of 18-21. Starting from the age of ten in girls, the pelvis becomes wider. This is an important period in the physical development of girls, because the progress of labor will depend on how well the bones of the pelvis grow together. In the process of the growth, an increase in body weight occurs mainly due to the increase in the volume and mass of skeletal muscles. The growth of muscle fibers in thickness is observed up to 30-35 years. After 50 years, atrophy of the fibers begins, and as a result, a decrease in muscle mass. The age feature of the muscles is the uneven growth of fibers in the muscles of the abdomen, back, pelvis, and lower leg. By the end of the first year, the muscles of the back and limbs are developing most rapidly, which is associated with the child's desire to walk and crawl. In younger schoolchildren, for example, the muscles that provide an upright position of the body, the movement of the fingers, and the deep muscles of the back and abdomen that are poorly developed, grow particularly rapidly. As a result, static efforts are contraindicated in children of primary school age. The increase in hand strength occurs gradually, but especially increases after 10 years. Physical development. Physical development is the long term changes in morphological and functional signs in the process of growth of the body and under the influence of factors contributing to the improvement of its condition (nutrition, physical education, etc.). The length of the body and its mass are integral indicators, allowing us to judge about the physical development of man. The growth of a person continues during the first 20 years of his life. As a rule, the increase in body length in men ends at the age of 18-20 years, in women – at 16-18 years. Further up to 60-65 years, the body length does not change, and after that, due to shortening (flattening) of intervertebral discs, changing posture and flattening of the arches of the body, the body length decreases by about 1-1.5 mm per year. The level of physical development depends on the innate instincts and complex social, economic, hygienic and other environmental conditions. 23

The constitution of a person is a set of individual, relatively stable features of a person. The structure, functional features of the body in different people are in many ways similar. There are the following types of constitution: asthenic, hyperstheniс and normosthenic. An elongated and flattened chest, long neck, thin and long limbs, often tall height characterize the asthenic type. The normosthenic type is characterized by a good development of bone and muscle tissue, proportional to the body height. In hyperstheniс type, body height is relatively low, the rib cage is round, the neck is short, and people of this type tend to obesity. The interest in the types of constitution is caused by their connection with different reactions to the same disease factors. According to the disproportion of the structure of the body, it is possible to reveal the disorders of the growth processes and the reasons for their appearance (endocrine, genetic, etc.). People of hypersthenic type are more susceptible to metabolic diseases, atherosclerosis, diseases of the biliary tract, but are less likely to suffer from infectious diseases and tuberculosis. People of normal stature often suffer from rheumatism, an ulcer, gastritis with high acidity. Asthenic people often suffer from gastritis with low acidity, hypotension. Hygiene of the musculoskeletal system. From the first day of school, children have to adapt to new pressures, new conditions. The lifestyle of the child, his habits imprint on the shape of the spine, posture. Posture is a relaxed posture of a person, depending on the interposition of individual parts of the body, on the general center of gravity of the body, and its features, the skeleton (i.e. the bends of the spinal column), the shape of the chest, the state of the muscular system and the joint apparatus. Depending on the severity of the spinal curvature, several types of posture are distinguished: normal (moderately pronounced curvature of all parts of the spine), straightened (mild curvature), stooped (pronounced curvature in the thoracic region), lordosis (pronounced curvature in the lumbar region), kyphosis (increased thoracic kyphosis, due to excessive curvature both in the cervical and lumbar spine). The lateral curvatures of the spinal column to the left or right of the vertical line form a scoliosis posture characterized by the asymmetrical position of the body, in particular, the shoulders and shoulder blades. One of the causes of scoliosis is weakness of the muscles on the side of the bulge of the spine as a result 24

of prolonged irregular position when sitting, carrying weight in one arm. Scoliosis, as a rule, is functional, regardless of the severity. It can affect blood circulation and respiration. It is proved that posture changes in the process of purposeful development of underdeveloped muscles, which contributes to their correction and prevention posture disorders. An important task of the physical education of schoolchildren is to develop a correct posture. It is of great importance because the most favorable working conditions are created for all internal organs, and the movements are most natural, rational, and economical. To prevent disorders of posture the child should follow a number of hygienic rules: to maintain constant control over the observance of the correct posture during eating, sleeping, during training sessions, to exercise. It is proved that during training sessions the most appropriate is direct landing with a slight inclination forward, and that the distance from the eyes to the notebook should be approximately equal to the length of the forearm and hand. The height of the seat should be equal to the length of the calf – 2-3 cm from the heel. The seat must have a back. When carrying the load, it is necessary to distribute the weight over the entire musculoskeletal system, to lift the load with a straight back, avoiding the backbone flexures, since the load on the intervertebral disks will be uneven. The shape of the chest is normally conical, cylindrical, flattened, and the volume of the chest, as well as the increase in its capabilities, depends on physical exercise. The shape of the legs is defined as normal, X-shaped, 0-shaped. There is a direct dependence on the history of diseases, such as beriberi (in childhood), and on insufficient development of muscles or excessive physical exertion. Vitamin D (calciferol) is called anti – rachitic, because rickets, the consequences of which are manifested in older children, is caused by hypovitaminosis in children of the first year of life and result in X- or 0-shaped legs. Excessive amounts of vitamin D in the body of the child reduces appetite, increases calcium phosphorrus content in the blood. The premature ossification of bone epiphyses may begin and affect the growth of the body in length. The shape of the feet may be normal, flattened and flat. The arch of the foot, performing the role of a shock absorber, protects the 25

internal organs, spinal cord and brain from excessive jolts when walking, jumping, and forced transfers of weight. The deformity of the feet, characterized by persistent descent of their arches, is called flatfoot. It is necessary to distinguish between the longitudinal (lowered internal arch) and transverse (lowered arch between the heads of the metatarsal bones). Flat feet are not a contraindication to physical exertion, but there are some limitations associated with weight lifting and repeated exercises of a hopping nature, causing pain in the arch of the foot. The reasons for flatfoot in childhood can be high-heeled shoes and sports shoes. The chest circumference is measured in three states (at maximum entry of the air, during the pause and at maximum expiration), the difference between inhalation and exhalation is called chest excursion. The average value is 5-7 cm (in athletes 10-12 cm or more). Modern advances in physiology, biology and other disciplines made it possible to objectively evaluate the effect of exercise on the human body. Muscular work speeds up the metabolism, and the fats literally "burn out". Exercise increases the redox processes in the body, increases the use of oxygen by tissues, and reduces cholesterol and fatty substances, which prevents the development of Atherosclerosis, improves the function of the cardiovascular system. Questions for self-control 1. What are the main signs of the classified bones? 2. What is the relationship between the bone structure and their function? 3. Tell us about the structure, chemical composition, growth of tubular bones. 4. What are the main parts of the skeleton and their functions? 5. What are the age features of the skeletal system? 6. What is the reason for reduction in the mobility of the joints with increasing age? 7. Name the basic physiological properties of the muscles. Describe the mechanism of muscle contraction. 8. Describe the basic motor qualities: strength, speed, endurance, accuracy. What is the sequence of their development? 9. Describe the features of the development of motor skills in children of the first year of life, 1-3 year-old children, in the periods of 3-7 years, 7-12 years, and 12-15 years old.

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CHAPTER

3

THE INTERNAL ENVIRONMENT OF THE BODY. COMPOSITION AND PROPERTIES OF BLOOD The body's internal environment consists of tissue fluid, lymph and blood. Thanks to them, the body temperature is maintained at a relatively constant level, as well as the amount of blood pressure, respiration rate, the content of sodium ions, potassium, calcium, chlorine, hydrogen, proteins, sugar and other substances. The ability to maintain the constancy of the internal environment is called homeostasis. In preserving the parameters of the internal environment, an important role belongs to the nervous and endocrine mechanisms. Tissue fluid fills the spaces between blood capillaries and tissue cells. It is characterized by a specific composition for individual organs, almost devoid of proteins. Its volume in humans is up to 26.5% of body weight. Tissue fluid provides the transition of amino acids, glucose, hormones, fats, oxygen and other biologically active substances from the blood to the cells of tissues and the removal of carbon dioxide and other decomposition products. Flowing from the organs into the lymphatic vessels, the tissue fluid turns into the lymph. Lymph is a fluid that circulates through the human lymphatic system. According to the composition of salts, it is close to blood plasma, characterized by a low content of proteins. By circulating through the lymphatic vessels, lymph facilitates the return of proteins from the intercellular spaces to the blood, the redistribution of water and the maintenance of normal metabolism in tissues, removal of waste products. Many nutrients 27

enter the lymphatic vessels of the intestine, in particular fats. Distortion of lymphatic drainage leads to metabolic disorders in the tissues, the appearance of edema. The lymphatic system provides immune response. Pathogens and cancer cells can spread with lymph. The lymph slowly moves through the lymphatic vessels, along which there are lymph nodes in which lymphocyte multiplication occurs. Thanks to lymphocytes, phagocytosis causes the destruction of microbes, foreign substances and the formation of antibodies. Lymph nodes are located in groups. Their largest accumulations are observed in the submandibular, axillary, ulnar, popliteal and inguinal areas. Many lymph nodes are present in the neck, in the chest and abdominal cavities and in the pelvic cavity. In inflammatory processes, they increase, become dense and can be easily felt. The composition and function of blood. Blood is an essential component of the body's internal environment. In an adult, its amount is 7-8% of body weight (5-6 l), in an infant – 10-20%. It is associated with metabolic processes that are more intensive. In children, starting from the age of seven, the amount of blood is kept, as in adults, at the level of 7% of body weight. Blood circulates through the vessels, but part of it (up to 40%) is in the blood depots (spleen, liver, lungs, skin, etc.). The release of blood from the depot occurs during muscular work, blood loss, a decrease in atmospheric pressure. Due to the movement of blood, continuous circulation of body fluids is maintained. Other 1% Proteins 8%

Plasma 55%

Water 91%

Whole blood

Leukocytes and platelets 0.9%

Formed element 45%

Erythrocytes 99.1%

Figure 1. Composition of blood. Percentages show the relative proportions of different components of plasma and formed elements.

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Blood is 55% plasma and 45% blood cells (red blood cells, white blood cells and platelets) (Figure 1). It has a weak alkaline reaction. For arterial blood, the pH is 7.4, the pH of the venous blood, due to the carbon dioxide content, is 7.35. The proportion of plasma in children is lower than in adults, and blood viscosity is higher. Blood plasma contains water (90-92%), mineral salts (0.9%), proteins (6.6-8%), fats (0.8%), carbohydrates (0.12%), enzymes, antibodies and other substances. The main plasma proteins are albumin (about 4.5% of the total amount of proteins), globulins (2-5%), and fibrinogen (0.2-0.4%). They provide plasma viscosity, maintain blood pH, prevent erythrocyte sedimentation, participate in maintaining immunity and blood coagulation, serve as carriers of a number of hormones, minerals, lipids, cholesterol. The composition of plasma salts is close to the composition of seawater. Red blood cells or erythrocytes. These are small (7-8 microns in diameter) nuclear-free cells having the shape of a biconcave disc. The absence of the nucleus allows the red blood cell to contain a large amount of hemoglobin, and its form contributes to an increase in its surface. In one μl of adult blood, there are 4.5-6 million erythrocytes, in children of primary school age – 5-6 million. The number of erythrocytes in the blood is not constant. It increases with elevation, large water losses, etc. An increase in their number is called erythrocytosis (erythremia), and a decrease is called erythropenia (anemia). Red blood cells are formed in the red bone marrow, and are destroyed in the spleen and liver. A human red blood cell live for about 120 days. Hemoglobin (HB) is a red iron containing pigment consisting of two parts: globin protein and a heme containing iron. In the pulmonary capillaries, hemoglobin, combining with oxygen, forms oxyhemoglobin (HbO2), which is present in arterial blood. In the tissue capillaries, oxyhemoglobin disintegrates with the release of oxygen, forming reduced hemoglobin (HbH). In combining with carbon dioxide in the venous blood, carbohemoglobin (HbCO2) is formed. The amount of hemoglobin is an indicator of health status. Normally, men contain 130-160 g/l of hemoglobin in the blood, and women – about 130 g/l. A child of primary school age contains 80-81% hemoglobin, the adults – 85%. With a decrease in the hemoglobin content in the blood, a disease called anemia occurs. It can be caused by bleeding, increased blood destruction, helminth infections, iron and 29

vitamin B12 deficiency. With any form of anemia, oxygen starvation occurs. The younger the child, the easier it develops anemia, which is explained by the weaker function of the blood in forming organs and insufficient oxygen supply due to the age characteristics of the respiratory tract. Adults and children suffering from anemia get tired more quickly; this disease is characterized by pale skin, shortness of breath, distraction of attention. In the body, in addition to hemoglobin, skeletal muscles contain myoglobin, which can add up to 14% of oxygen in the tissues. This is a reserve for the case of oxygen deficiency with intensive muscular work. In addition, pathological hemoglobin compounds are known. These are a compound with carbon monoxide – carboxyhemoglobin (HbCO) and methemoglobin (HbOH), which form when strong oxidezing agents enter the blood (aniline, potassium permanganate). The addition of carbon monoxide to hemoglobin occurs 300 times faster than that of oxygen. Carboxyhemoglobin is more durable than oxyhemoglobin. Carbon monoxide poisoning is life threatening. First aid for such poisoning is to provide clean air access to the lungs. In defending blood with the addition of substances that prevent clotting, erythrocyte sedimentation is observed. The erythrocyte sedimentation rate (ESR) depends on the properties of the plasma, primarily on the content of globulin and fibrinogen proteins. The concentration of the latter increases in inflammatory processes, pregnancy. In general, ESR in men is 1-10 mm/h, in women – 2-15 mm/h. During pregnancy, it increases to 40-50 mm/h. Leukocytes. Leukocytes are called colorless blood cells. By the features of the structure, we distinguish granular (neutrophils, basophils, eosinophils) and non-granular (lymphocytes and monocytes) leukocytes. Each type of white blood cells performs certain functions. Their percentage in the blood is called leukocyte formula (neutrophils – 75%, basophils – 0.5%, eosinophil's – 1-4%, lymphocytes 25-30%). It has a diagnostic value and is used in determining the stage of the disease. In scarlet fever, sore throat, rheumatism the increase in the percentage of lymphocytes is observed. With allergic diseases, the percentage of eosinophils increases, with some other diseases the percentage of neutrophils and basophils is observed (Figure 2). The number of leukocytes in one μl of adult blood ranges 49 thousand, in children – 9-12 thousand. A decrease in their number 30

in the blood causes leukopenia. It is observed in various diseases due to inhibition of leukocyte production. An increase in the number of leukocytes is called leukocytosis. It may be physiological due to the redistribution of blood after a meal, physical work, as well as with the increase of body temperature (for example, after taking a bath), or occur in inflammatory diseases. The leukocyte formula in children also changes with fatigue, in crying, an exciting game.

Monocyte

Lymphocyte

Macrophage

Neutrophil

Erythrocyte

Eosinophil

Basophil

Platelets

Figure 2. Blood cells (©Terese Winslow, 2015)

The life span of leukocytes varies from a few hours (neutrophils) to 100-200 or more days (lymphocytes). Granular leukocytes are formed in the red bone marrow, monocytes – in the liver and spleen, lymphocytes – in the thymus, bone marrow, and then multiply in the spleen, lymph nodes. The main function of leukocytes is their ability to protect the body from infection. Each type of white blood cells performs certain functions. Neutrophils and monocytes are able to actively capture and absorb bacteria, cell fragments, and solid particles. This phenomenon is called phagocytosis or intracellular digestion. Eosinophils absorb and neutralize allergens and toxins of parasites (viruses, bacteria, protozoa, flat and roundworms). Lymphocytes produce antibodies that make the body immune to infectious diseases. Platelets. Platelets are enucleate blood formations of a round or oval shape with a diameter of 2-5 microns. They a formed in the red bone marrow and live for 8-11 days. In a microliter of adult blood 20031

400 thousand platelets are contained, in children – 100-200 thousand. They possess specific granules containing substances involved in blood coagulation. Blood coagulation (hemostasis) is a biological process, accompanied by the conversion of liquid blood into an elastic clot because of the transition of the fibrinogen protein dissolved in the blood plasma to insoluble fibrin. This is a protective reaction of the body that prevents blood loss in disruption of the integrity of blood vessels. The process of blood coagulation is regulated by the nervous and endocrine systems and caused by the interaction of components of the vascular wall, platelets and a number of plasma proteins, called coagulation factors. In this process, platelets begin to adhere to the damaged vascular wall and release enzymes that, in the presence of calcium salts, with the participation of vitamin K, convert prothrombin protein, synthesized in the liver into thrombin. The latter contributes to the transition of the fibrinogen protein dissolved in plasma into fibrin, which in polymerizing forms thin filaments that hold red blood cells. As a result, a clot that clogs the affected area of the vessel forms, and the bleeding stops. Coagulation time in humans ranges from five to 12 minutes. Blood groups. Immunological signs of blood caused by specific substances – antigens, allow dividing it into groups. In erythrocytes, there are special proteins (agglutinogens) of two types, which are commonly designated as A and B. The blood plasma contains proteins (agglutinins) α and β. Agglutinins α are able to glue agglutinogens A, agglutinins β – agglutinogens B. Agglutinin α and agglutinogen A or β and B are never found in human blood at the same time, the blood of a man is divided into four groups: Group I (0) – α and β, II (A) – A and β, III (B) – B and α, IV (A and B) – 0. About 85% of people have erythrocyte protein called a Rhesus factor (Rh). They are called Rh-positive (Rh+). The rest who do not have this protein are called Rh-negative (Rh-). Blood groups are determined by the erythrocyte adhesion reaction (hemagglutination). Blood transfusion should be carried out taking into account the compatibility of blood groups and Rh factor. Donor agglutinogens of the same name should not occur with the recipient's agglutinin. People with group I are not universal donors, as it was previously thought, 32

because in 10-20% of cases they have additional agglutinogens and agglutinins. It has been established that no more than 500ml of donated blood of another group can be transfused, and then only the blood of the relevant own group. Blood of the II group can transfused to people with the II and IV groups. Blood of donors of the III group can be transfused to recipients of the III and IV groups; the IV group is only transferred to the owners of this group. People whose blood does not contain the Rh factor cannot be infused with the blood of people with a positive Rh factor, since rhesus conflict occurs. In this regard, the cause of fetal death in some pregnant women was established. The Rh factor of the fetus crosses the placenta and penetrates into the mother's blood and the reverse diffusion of antiserum substances into the fetus's blood occurs causing hemolysis of the erythrocytes and subsequent death of the fetus. Such a phenomenon accompanies the development of the Rh-positive fetus in the Rh-negative mother. Immunity. Immunological disorders: allergies. The Russian scientist I.I. Mechnikov, who in 1883 made the first reports on phagocytosis, started the study of the protective properties of white blood cells. An important role in protecting the body from infection also belongs to special plasma proteins (antibodies), which are produced by plasma cells (modified by lymphocytes during the immune response). Antibodies are contained in the globulin fraction of blood proteins (immunoglobulins) and circulate freely with the plasma current. They provide the body's ability to protect its own integrity and biological identity from damaging agents, in other words, immunity. The damaging factors, or antigens, are substances that are perceived by the body as foreign and therefore cause a specific immune response. It is the antigen antibody response, aimed at neutralizing pathogens, their metabolic products (toxins), etc. There are innate and acquired immunity. Inborn immunity is a hereditary trait of all species. It is species-specific. Thus, a human is immune to pathogens of cattle plague, chicken cholera, etc. Natural passive immunity is characteristic of a newborn when mother's antibodies are present in him for about a year. Then a natural active immunity is switched, which is provided by the immune memory. If the immune response developed after an infectious disease, then it called acquired. Modern medicine has powerful tools that allow creating 33

immunity artificially by means of protective vaccinations, therapeutic measures, etc. After the introduction of the vaccine (a weakened or killed culture of the infectious disease pathogen), the body produces the corresponding antibodies to the antigens of the pathogen and the person becomes immune to a specific disease. This is an active acquired immunity. Currently, active vaccines against smallpox, rabies, tetanus, and tuberculosis are available. With the introduction of ready-made antibodies into the body, an artificial passive immunity occurs. Impaired immunity manifests itself in the form of allergies and AIDS. Today, an allergy is understood as an inadequate immune response of the body to a certain substance (allergen) associated with an increased sensitivity to it. An allergen is an antigen that causes allergies. Why one antigen may be an allergen, and another one cannot, it is still not completely clear. This is determined by the physical and chemical properties of the antigen and the characteristics of the immune system of the body. All allergens can divided into two large groups: 1. Endogenous allergens; 2. Exogenous allergens. The first group refers to those cases where, for some reason, an immune response to the body's own components develops. The second group refers to allergens present in the environment. 1. Allergens of animal origin. Severe allergenicity inherent in the cells of the epithelial tissues is caused by wool, dandruff, feathers of birds. In addition, the excreted matter of warm – blooded animals – urine, saliva, etc., causes allergy. Vegetable allergens. Pollen of many plants can cause allergies. Pollen of certain groups of plants may be present in the air. In the spring, pollen of blossoming trees (birch, hazel, oak) appears. In the period from late May until the mid of August flowering of cereal grasses (timothy grass, bluegrass, etc.) may also induce allergic reactions. 3. Bacterial and fungal allergens. These are allergens of bacteria (staphylococcus, streptococcus) and fungi (mold, yeast). 4. Dust allergens. This group combines allergens that are part of house dust (waste products). Allergens are the library dust, industrial dust.

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5. Drug allergens. Virtually all of the currently known drugs can cause allergies, acting as full allergens. Most often, drugs such as antibiotics (penicillin, streptomycin, novocain, therapeutic heterologous sera) cause allergies. 6. Food allergens. Allergies to a variety of food products may occur – milk, eggs, fish, and honey most often act as allergens. 7. Intensive allergens. These allergens are the poison of stinging insects. The symptoms of an allergic disease occur only in contact with a specific allergen. As soon as this contact ceases, the symptoms of the disease disappear. Questions for self-control 1. Name the organs that make up the blood system. What is the composition of blood plasma? 2. What is the significance of the constancy of the blood pH reaction? 3. Describe the structure and function of red blood cells. 4. What types of leukocytes do you know and what functions do they perform? What is called phagocytosis? 5. What is leukocyte blood count? How does it change with age in children? 6. How does the blood composition of children change with age?

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CHAPTER

4

PHYSIOLOGY OF THE CARDIOVASCULAR SYSTEM AND AGE FEATURES Structure and age features of the cardiovascular system. The work of the circulatory system provides continuous transportation of nutrients to the tissues and organs and the removal of the products of metabolism from them. The movement of blood through the vessels, providing the metabolism between the body and the external environment, is called the blood circulation. It occurs with the help of special bodies, united in a single functional system. The circulatory system includes the heart and blood vessels (arteries, capillaries, veins) that permeate all organs of the human body. The heart is the main organ of the circulatory system. It is a hollow muscular organ consisting of four chambers: two atria (right and left), and two ventricles (right and left). The right atrium is connected with the right ventricle through the tricuspid valve, and the left atrium with the left ventricle – through the bicuspid (mitral) valve. Near the holes of large vessels (aorta and pulmonary trunk) leaving the heart there are three semilunar valves. The latter consist of three half – moon pockets, facing the base of the ventricles, and free edges in the direction of the vessels. The value of the valves is that they do not allow the reverse flow of blood. The walls of the heart consist of three layers: the inner – endocardium, middle – myocardium and the outer layer is epicardium. The whole heart is enclosed in the pericardium. The latter, together with the epicardium, forms two sheets of the serous membrane of the heart, 36

between which there is a slit – a space filled with serous fluid. Such a structure of the pericardial bag helps to reduce friction in cardiac contraction. The heart muscle is similar in structure to the striated muscles, however, it is characterized by the ability to automatically and rhythmically contract due to the impulses that occur in the heart itself, regardless of external influences (automatic heart). The average heart mass of an adult is about 250 g for women and about 330 g for men. In the first two years of life and during puberty (12-15 years), the most intensive growth of the heart is observed. In children aged 7 to 10 years, it grows slowly, significantly lagging behind the increase in body weight and body size. In appearance, the heart of a child differs from the heart of an adult only in size and clearer boundaries of the oval fossa (deepening in the septum between the atria). The oval fossa is a trace of the former oval hole in the prenatal period of development. If the oval hole does not close after birth, it is defined as a congenital defect. Acquired heart defects, which are the consequences of rheumatism, arrhythmias, and varicose veins, are more common. In children, a continuous growth and functional improvement of the cardiovascular system constantly occurs. Especially vigorously, the heart grows and improves in children from 2 to 6 years, as well as during puberty. The heart of a newborn has a flattened cone shape, oval or spherical shape due to insufficient ventricular development and relatively large atrial sizes. Only by the age of 10-14 years does the heart take on the same shape as in an adult. Due to the high standing of the diaphragm, the heart of the newborn is located horizontally. Oblique position the heart takes in the first year of life. The mass of the heart of a newborn is 0.8% of the total body mass; it is relatively more than that of an adult. The right and left ventricles, are the same in thickness, their walls are 5 mm. The atrium and the major vessels have comparatively large sizes. By the end of the first year, the weight of the heart doubles, by 3 years it triples. In preschool and primary school years, heart growth slows down and accelerates again during puberty. By the age of 17, the heart mass increases 10 times. Irregular growth and compartments of the heart. The left ventricle significantly increases its volume, by the age of 4 months it is twice the weight of the right one. The thickness of the walls of the ventricles 37

in the newborn is 5.5 mm, in the future, the thickness of the left ventricle increases to 12 mm; the right one is up to 6-7 mm. The volume of the heart at birth is about 22 cm3, during the first year it increases by 20 cm3, and subsequently it increases annually by 6-10 cm3. At the same time, the diameter of the valve holes increases. In children, the heart is higher than in adults. The volume of the heart in children is larger relative to the volume of the chest than in adults. In a newborn, the apex of the heart is formed by both ventricles, by 6 months – only by the left. The projection of the heart by 1.5 years from the fourth intercostal space shifts to the fifth intercostal space. In childhood, a qualitative restructuring of the heart muscle occurs. In young children, the muscle of the heart is not differentiated. Muscle of the heart consists of thin, poorly separated myofibrils that contain a large number of oval nuclei. Transverse striation is absent. Connective tissue begins to develop. There are very few elastic elements; in early childhood, muscle fibers closely adjoin each other. As the child grows the muscle fibers thicken, coarse connective tissue appears. The form of the nucleus becomes rod-shaped, transverse striation of the muscles appears, by the age of 2-3 years, the histological differentiation of the myocardium is completed. Other parts of the heart are also undergo improvement. As the child grows, the conduction of the cardiac system improves. In early childhood, the heart is underdeveloped; its fibers are not clearly contoured. In older children, the cardiac conduction system is re-modulated; therefore, rhythm disturbances are often found in children. The work of the heart is carried out by superficial and deep plexuses formed by the fibers of the vagus nerve and cervical sympathetic nodes in contact with the ganglia of the sinus and atrioventricular nodes in the walls of the right atrium. The branches of the vagus nerve complete their development by 3-4 years. Until this age, cardiac activity is regulated by the sympathetic system. This explains the physiological increase in heart rate in children of the first 3 years of life. Under the influence of the vagus nerve, the heart rhythm is reduced and an arrhythmia of the respiratory type appears, the intervals between heart contractions are lengthened. Myocardial functions in children, such as automatism, conduction, contractility, are carried out in the same way as in adults (Figure 3).

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Aorta Pulmonary artery

Super vena cava

Pulmonary veins Sinoatrial node

Mitral valve

Artioventricular (AV) node

Purkinje fibers

Tricuspid valve

Right and left branches Of AV bundle

Right ventricle

Left ventricle

Inferior vena cava

Figure 3. Structure of the Heart

The vessels feed and distribute the blood to the organs and tissues of the child. The widths of the arteries are not equal to those of the veins. The ratio of their lumen is 1:1, then the venous bed becomes wider, by the age of 16, this ratio is 1:2. The growth of arteries and veins often does not correspond to the growth of the heart. The walls of the arteries are more elastic than the walls of the veins. This is associated with lower, than in adults, peripheral resistance, blood pressure and blood flow velocity. The structure of the arteries also changes. In newborns, the walls of the vessels are thin, with weak muscular and elastic fibers. Up to 5 years, the muscular layer quickly grows, at 5-8 years all the membranes of the vessels are evenly developed; by the age of 12, the structure of the vessels in children is the same as in adults. The pulse rate in children depends on age. For a newborn, it is 160-140 beats per 1 minute, 110-140 – at 1 year, 100 – at 5 years, 8090 – at 10 years, and 80 – at 15 years. With age, systolic blood pressure increases, there is a tendency to the increase in diastolic pressure.

39

Arterial systolic pressure is 90 + 2xn, diastolic is 60 + 2xn, where n is the child's age in years. For children under one, the systolic pressure is 75 + n, where n is the age of the child in months. Diastolic blood pressure is equal to systolic pressure minus 10 mm Hg. Heart and vessels in puberty. At puberty, an intensive growth of various organs and systems occurs. In this period, there may be distortions of their functioning due to disturbances in their relationships and coordination of functions. In adolescents, due to the growth characteristics of both the heart and the whole body, a relatively small weight and volume of the heart compared to the mass and volume of the body are observed. The ratio of the volume of the body to the volume of the heart in children is 50%, in the adults it is 60%, and in the pubertal period, it is 90%. In addition, there are anatomical features of the cardiovascular system in adolescents, which are associated with the ratio of the volume of the heart and blood vessels. In adolescents, the heart volume increases faster than the capacity of the vascular network, this increases peripheral resistance, which leads to the hypertrophic variant in the growth of the heart. In adolescents with abnormalities in the age evolution of the heart, sympathetic regulation prevails. Thus, children have functional features of the circulatory system, which are characterized by: 1) A high level of endurance of the children's heart due to its rather large mass, good blood supply; 2) Physiological tachycardia caused by a small volume of the heart with a high need of the child's body for oxygen; 3) Low blood pressure with a small volume of blood coming in with each heartbeat, as well as low peripheral vascular resistance; 4) Uneven growth of the heart and related functional disorders. The work of the heart. The function of the heart is the rhythmic pumping of blood in the arteries; the blood comes to the heart through the veins. An adult's heart contracts about 60-80 times per minute in a resting state of the body. More than half of this time, it rests and relaxes. The increase in the heart rate to 90-150 beats per minute is called tachycardia and is observed in the intense muscular work and emotional sates. With a rarer heart rate, 40-50 beats per minute, bradycardia occurs (in athletes). The continuous activity of the heart consists 40

of the cycles, each of which consists of contraction (systole) and relaxation (diastole). There are three phases of cardiac activity: atrial contraction, ventricular contraction and pause (simultaneous relaxation of the atria and ventricles). Atrial systole lasts for 0.1 s, ventricles – 0.3, total pause – 0.4 s. Thus, during the entire cycle of the atrium work of 0.1 s and rest of 0.7 c, the ventricles work for 0.3 s. and rest for 0.5 s. This explains the ability of the heart muscle to work without tiring, throughout the life of individual. High performance of the heart muscle is caused by the increased blood supply to the heart. Approximately 10% of the blood released by the left ventricle into the aorta enters the arteries extending from it. These feed the heart. The baby's heart muscle consumes a large amount of oxygen. In infancy, per 1 kg of body weight the amount of oxygen required is 2-3 times more than in an adult age, so long stay in the fresh air is important for children. The amount of blood emitted by the heart per minute is called the minute volume of blood. Normally, in an adult it is 4-5 liters, and in a seven year – old child – about 2 liters. During exercise, the minute blood volume reaches 25-30 liters. In trained people, this happens due to an increase in heart rate; in those who are not trained, it is caused by the increase in the systolic blood volume. The volume of blood ejected per systole is called systolic. It is 60-70 ml. Blood vessels. Arteries. Blood vessels that carry oxygen in the blood from the heart to the organs and tissues (only the pulmonary artery carries venous blood) are called arteries. In humans, the diameter of the arteries varies from 0.4 to 2.5 cm. The total blood volume in the arterial system averages 950 ml. Arteries gradually branch out into smaller and smaller vessels – arterioles, which pass into the capillaries. Capillaries. The smallest vessels (average diameter of about 7 microns), penetrating human organs and tissues are called capillaries. They connect small arteries with small veins. Through the walls of capillaries consisting of endothelium cells, gases and other substances are exchanged between blood and various tissues (Figure 4).

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Ven

Artery Elastic tissue Inner tunic Middle tunic Outer tunic Blood flow

Valve

Venule

Arteriole

Capillary

Figure 4. Sections of small blood vessels

Veins. Blood vessels carrying blood saturated with carbon dioxide, metabolic products, hormones and other substances from the tissues and organs to the heart (except pulmonary veins that carry arterial blood) are called veins. Circles of blood circulation. The English physician W. Harvey first described the movement of blood through the vessels in 1628. In humans, blood moves along a closed cardiovascular system consisting of a greater and lesser circulation. The big circle of blood circulation begins from a left ventricle and ends in the right auricle. From the left ventricle of the heart, blood enters the largest arterial vessel, the aorta. Numerous arteries depart from the aorta, which, upon entering the organ, divide into smaller vessels and, finally, pass into the capillaries. From the capillaries, blood is collected into small veins, which, merging, form vessels of larger dimensions. The two largest veins – the upper hollow and the lower hollow veins carry blood to the right atrium. Through the capillaries of the systemic circulation, the cells of the body receive oxygen and nutrients, as well as carry off carbon dioxide and other decomposition products. Arterial blood flows in all arteries of this circle, and venous blood flows in its veins. 42

The pulmonary circulation starts from the right ventricle and ends in the left atrium. From the right ventricle of the heart, venous blood enters the pulmonary artery, which soon divides into two branches that carry blood to the right and left lung. In the lungs, arteries are branched into capillaries, where gas exchange occurs: blood gives off carbon dioxide and is saturated with oxygen. Oxygenated arterial blood flows through the pulmonary veins into the left atrium. Consequently, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins. The movement of blood through the vessels is possible due to the difference in pressure at the beginning and at the end of each circulation, which is caused by the work of the heart. Blood pressure is higher in the left ventricle and aorta than in the vena cava and in the right atrium. The pressure difference in these areas ensures the movement of blood in the systemic circulation. High pressure in the right ventricle and pulmonary artery and low pressure in the pulmonary veins and the left atrium ensure the movement of blood in the pulmonary circulation. The main reason for the movement of blood through the veins is the difference in pressure at the beginning and end of the venous system, so the movement of blood through the veins occurs in the direction of the heart. This is facilitated by the suction of the chest ("chest-breathing pump") and the contraction of skeletal muscles ("muscle pump"). During inhalation, the pressure in the chest decreases and becomes negative, i.e. below the atmospheric pressure. In this case, the pressure difference in the large and small veins, i.e. at the beginning and at the end of the venous system, increases and the blood is sent to the heart. Skeletal muscles, contracting, compress the veins, which also contributes to the movement of blood to the heart. Venous valves, having the form of pockets facing openings towards the heart, also hinder the backflow of blood. When they are filled, they close, and one way to the heart remains for the blood. The movement of blood in the capillaries is caused by the changes in the lumens of the supplying small arteries: their expansion enhances the blood flow in the capillaries, while narrowing – reduces. Pulse. Periodic jerky expansion of the arterial walls, synchronous with the contraction of the heart, is called the pulse. The pulse can determine the number of heart beats per minute. An adult person has an average heart rate of 60-80 beats per minute, a newborn has about 130, a 43

7-10-year-old child has 85-90, and a teenager of 14-15 years old has 7580. In places where the arteries are located on the bone and lie directly under the skin (radial bone, temporal bone), the pulse is easily palpable. Blood pressure. The pressure on the walls of blood vessels and heart chambers, resulting from the contraction of the heart, which injects blood into the vascular system, is called blood pressure. The most important medical and physiological indicator of the state of the circulatory system is the pressure in the aorta and large arteries – blood pressure. Usually, we distinguish a maximum (systolic) blood pressure and a minimum (diastolic). The pressure level in the arteries during systole of the heart in a healthy person between the ages of 15 and 50 is about 120 mm Hg, and during diastole, it is about 80 mm Hg. There are diseases associated with changes in blood pressure: hypertension (an increase in the blood pressure), hypotension (a decrease in the blood pressure). There are age features of pressure fluctuations. After 50 years, it can rise up to 135-140 mm Hg, after 70 years – up to 160 mm Hg. In children, the arterial pressure is lower than in adults. Therefore, in a newborn, it is 60 mm Hg, at 1 year – 90/50 mm Hg, at 7 years it is 88/52 mm Hg. The indicators of blood pressure are affected by: 1) the work of the heart and the strength of the heartbeat; 2) the size of the lumen of blood vessels and the tone of their walls; 3) the amount of blood circulating in the vessels; 4) blood viscosity. Regulation of cardiac activity. The activity of the heart is regulated by nervous and humoral factors. The vegetative nervous system innervates the heart. Sympathetic nerves increase the rhythm and increase the strength of contractions; parasympathetic ones slow down the rhythm and weaken the strength of the heart contractions. Humoral regulation is carried out with the help of special chemoreceptors present in large vessels, which are excited under the influence of changes in the blood composition. The increase in the concentration of carbon dioxide in the blood irritates these receptors and reflexively enhances the work of the heart. Biologically active substances entering the blood also play a large role. Adrenaline, which is formed in the adrenal glands and in the endings of the sympathetic nerves, also strengthens the activity of the heart. Acetylcholine, which is a mediator of parasympathetic nerve endings, on the contrary, slows the heart rate. Hygiene of the cardiovascular system. The normal activity of the human body is possible only with a well-developed cardiovascular 44

system. The speed of blood flow will determine the degree of blood supply to the organs and tissues and the rate of removal of waste products. During physical work, the need of organs for oxygen increases simultaneously with the increase in the heart rate. A strong heart muscle can only provide this work. To be resilient to a variety of work, it is important to train the heart, to increase the strength of its muscles. Physical labor, physical training develop the heart muscle. To ensure the normal function of the cardiovascular system, a person must begin his day with morning exercises, especially the people whose professsions are not connected with physical labor. To enrich the blood with oxygen, it is better to do exercises in the open air. Alcohol, nicotine, and drugs adversely affect the function of the cardiovascular system. People who consume alcohol, heavy smokers, more often than other people do, develop spasms of the heart vessels; they often develop atherosclerosis – a disease associated with the changes in the walls of blood vessels. In addition, with excessive consumption of animal fats, cholesterol can be deposited on the walls of blood vessels. These deposits, first in the form of plaques, then tapes, can significantly limit the blood flow or lead to the rupture of the vessel. At a certain level of increased cholesterol in the blood, the likelihood of a heart attack increases. At the levels below 5.2 mg per liter of blood, cholesterol is not a significant factor in heart disease. Mild cholesterol content is considered to be 5.2-6.5 mg per liter, 6.5-7.8 is a moderate level, over 7.8 mg per is a high level. Some studies have shown that diets containing unsaturated fats of vegetable origin are preferable and allow maintaining normal cholesterol levels. These diets, as well as malic acid, promote to even lower blood cholesterol. Questions for self-control 1. What is the physiological role of the heart? 2. Name the chambers of the heart, the holes through which the chambers are connected with each other. 3. Describe the purpose of the large and small circles of blood circulation. 4. What shells form the wall of the heart? 5. List the basic properties of the heart muscle. How does the excitability of the heart muscle change with contraction? 7. What parts are isolated in the cardiac conduction system? Where are they located? 9. Describe the cardiac cycle, its phases and duration. 10. What vessels are called exchange, trunk, capacitive, resistant? Name the functions performed by different vessels.

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CHAPTER

5

PHYSIOLOGY OF RESPIRATORY ORGANS AND AGE FEATURES The lungs and airways begin to develop in the embryo at week 3 from the mesodermal mesenchyme. Later on, in the process of growth, a lobar structure of the lungs is formed, after 6 months the alveoli are formed. At 6 months, the surface of the alveoli start being covered with a protein and lipid liner, which is a surfactant. Its presence is a necessary condition for normal aeration of the lungs after birth. With the lack of surfactant, when the air enters the lungs, the alveoli collapse, leading to severe respiratory disorders without treatment. The lungs of the fetus as an organ of external respiration do not function. However, they are not in a dormant state, the alveoli and bronchi of the fetus are filled with fluid. The fetus, starting from the 11th week, shows periodic contractions of the inspiratory muscles in the diaphragm and intercostal muscles. At the end of pregnancy, fetal respiratory movements take 30-70% of the total time. The frequency of respiratory movements usually increases at night and in the morning, as well as with the increase in the motor activity of the mother. Respiratory movements are necessary for the normal development of the lungs. Later the development of alveoli and the increase in lung mass slows down. In addition, the respiratory movements of the fetus are a kind of preparation of the respiratory system for breathing after birth. Birth causes dramatic changes in the state of the respiratory center, located in the medulla oblongata, leading to the onset of ventilation. The first breath occurs, usually in 15-70 seconds after birth. The main conditions for the occurrence of the first breath are as follows: 46

– The increase in the blood of humoral irritants of the respiratory center, CO2, H + and lack of O2; – A sharp increase in the flow of sensitive impulses from skin receptors (cold, tactile), proprioceptors, vestibular receptors. These impulses activate the reticular formation of the brain stem, which increases the excitability of the neurons of the respiratory center. – Elimination of sources of inhibition of the respiratory center. Irritation of receptors located in the area of the nostrils by the liquid, greatly inhibits breathing (diver's reflex). Therefore, immediately after the appearance of the head of the fetus, obstetricians remove mucus and amniotic fluid from the face cavities. Thus, the occurrence of the first breath is the result of the simultaneous action of a number of factors. The beginning of the ventilation of the lungs is associated with the beginning of functioning of the pulmonary circulation. Blood flow through the pulmonary capillaries increases dramatically. Pulmonary fluid is absorbed from the lungs into the bloodstream; some of the fluid is absorbed into the lymph. In small children, quiet breathing is diaphragmatic. This is due to the structural features of the chest. The ribs are located at a large angle to the spine, so the contraction of the intercostal muscles less effectively changes the volume of the chest cavity. The energy cost of breathing for a child is much higher than that for an adult. The reason is the narrow airways and their high aerodynamic resistance, as well as low elasticity of the lung tissue. Another distinguishing feature more intensive ventilation of the lungs in terms of a kilogram of body weight in order to satisfy a high level of oxidative processes and lower permeability of the pulmonary alveoli for O2 and CO2. Thus, in newborns, the respiratory rate is 44 cycles per minute, the respiratory volume is 16 ml, and the minute respiration volume is 720 ml/min. In children of 5-8 years of age, respiratory rate decreases and reaches 25-22 cycles per minute, tidal volume – 160-240 ml, and minute respiration volume is 3900-5350 ml/min. In adolescents, respiratory rate ranges 18 to 17 cycles per minute, tidal volume – 330 to 450 ml, the minute volume of respiration – 6000 to 7700 ml/min. These values are closest to the level of an adult. With the age, the vital capacity of the lungs and the permeability of the pulmonary alveoli for O2 and CO2 increase. This is due to an increase in body mass and working muscles, an increase in the need 47

for energy resources. In addition, breathing becomes more economical, as evidenced by the decrease in respiration rate and tidal volume. The greatest morphological and functional changes in the lungs cover the age period lasting up to 7-8 years. At this age, there is an intense differentiation of the bronchial tree and an increase in the number of alveoli. The growth of lung volumes is also associated with the changes in the diameter of the alveoli. In the period from seven to 12 years, the diameter of the alveoli doubles, by the adult state it increases three times. The total surface of the alveoli increases 20 times. Thus, the development of the respiratory function of the lungs is uneven. The most intensive development is observed at the age of 68, 10-13, and 15-16 years. In these age periods, the growth and expansion of the tracheobronchial tree predominates. In addition, at this time, the process of differentiation of lung tissue proceeds most intensively, and is completed by the age of 8-12. Critical periods for the development of the functional capabilities of the respiratory system is observed at the age of 9-10 and 12-13 years. The stages of maturation of the regulatory functions of the lungs are divided into three periods: 13-14 years (chemoreceptor), 15-16 years (mechanoreceptor), 17 years and older (central). Structure and function of the respiratory system. Specialized organs for gas exchange between the organism and the external environment form the respiratory system, which in humans is represented by the lungs, located in the chest cavity, and the airways, the nasal cavity, the larynx, the trachea, the bronchi. Conditionally, there are three main processes in respiration: between the external environment and the lungs, between the alveolar air and blood, between the blood and tissues. During inhalation, air enters through the nostrils into the nasal cavity, which is divided into two halves by a bone and cartilage septum. The nasal cavity is lined with ciliated epithelium, which removes dust from the air. In the mucous membrane, there are a dense network of capillaries, due to which the inhaled air is warmed, and the olfactory receptors provide the distinction of odors. In children, the maxillary cavities (sinuses of the upper jaw) are underdeveloped, the nasal passages are narrow, and the mucous membrane swells at the slightest inflammation, making breathing difficult. The maxillary cavities reach their full development only during the period of tooth change. Holes 48

connecting the nasal cavity with the nasopharynx (frontal sinus, choanas) are formed by the age of fifteen (Figure 5). The nasopharynx is the upper part of the pharynx, where the pathways of the digestive and respiratory systems intersect. Food passes from the pharynx through the esophagus into the stomach, and the air – through the larynx into the trachea. When food is being swallowed, the entrance to the larynx closes with special cartilage.

Nasal cavity Nostril Oral cavity

Pharynx

Larynx Trachea Right main bronchus

Left main bronchus

Right lung

Left lung Diaphragm

Figure 5. The respiratory system (©The Respiratory System.com, 2017)

The larynx has the shape of a funnel formed by cartilage: thyroid, scaly, cricoid, horn-shaped, wedge-shaped, and epiglottis. Thyroid cartilage consists of two plates connecting at an angle (straight for men – Adam's apple, blunt for women). Between the thyroid and scaly cartilages, the vocal cords (paired elastic folds of the mucous membrane) stretch and limit the glottis. Fluctuations of the vocal cords during exhalation produce sounds. In humans, in the reproduction of articulate speech, in addition to the vocal cords, the tongue, lips, cheeks, soft palate, and epiglottis participate. In the first years of life, the larynx grows slowly and has no sex differences. Before the period of puberty, its growth is accelerated, and the size increases (for men it is one third 49

longer). By the age of 11-12, the growth of the vocal cords is accelerated. In boys (1.3 cm), they are longer than in girls (1.2 cm). By the age of 20, they reach 2.4 cm in young men, and 1.6 cm in girls. At puberty, a change (mutation) of the voice occurs, which is especially pronounced in boys. At this time, thickening and redness of the vocal cords is observed. The height of the voice depends on their thickness, as well as the length and degree of tension. The air from the larynx enters the trachea (or respiratory throat), the length of which is 8.5-15 cm. Its basis is formed by 16-20 cartilaginous rings open at the back. The trachea is tightly adherent to the esophagus. Therefore, the absence of cartilage on the posterior wall is necessary because the food bolus, passing through the esophagus, does not experience resistance from the trachea. The growth of the trachea occurs evenly, with the exception of the first year of life and puberty, when it is most intense. The trachea is divided into two cartilaginous bronchial tubes that go to the lungs. Its immediate continuation is the right bronchus; it is shorter and wider than the left one and consists of 6-8 cartilaginous semi-rings. The left one has 9-12 semi-rings. Bronchi branch, forming a bronchial tree. From the main bronchi lobar, then segmental ones ramify. By the time the child is born, the branching of the bronchial tree reaches 18 orders, and in an adult, it has 23 orders. The thinnest branches of the bronchial tree are called bronchioles. The respiratory part of the respiratory system is the lungs. They are a paired organ in the form of a cone with a thickened base and a tip that protrudes 1-2 cm above the first rib. On the inner side of each lung, there are gates through which the bronchi, arteries, veins, nerves and lymphatic vessels pass. The right lung consists of 3, and the left of 2 lobes. On both lungs, there is a slanting slit, starting 6-7 cm below the top of the lung and going to its base. On the right lung, there is also a less deep, horizontal slit. Each lung, as well as the inner surface of the wall of the chest cavity is covered with pleura (a thin layer of smooth epithelium), which forms the pulmonary and parietal sheets. Between them, there is a pleural cavity with a small amount of pleural fluid, which facilitates sliding of the pleura when breathing. The mass of each lung in adulthood ranges from 0.5 to 0.6 kg. In newborns, the mass of the lungs is 50 g; in primary schoolchildren, it is about 400 g. The color of the lungs in childhood is pale pink, and then it becomes 50

darker due to dust and solid particles, which are deposited in the connective tissue basis of the lungs (Figure 6). The structural unit of the lung is acinus. It is a branching of one terminal bronchiole. The latter ends with sacs, the walls of which are formed by the alveoli. The alveoli are bubbles of arbitrary shape, divided by partitions, which are intertwined with a thick network of capillaries. Their total number exceeds 700 million, and their total surface in an adult is about 100 m2. External breathing is provided by inhalation and exhalation. Inhalation is carried out by reducing the intercostal muscles and diaphragm, which, stretching the chest, increase its volume, which helps to reduce pressure in the pleural cavity. In a deep breath, in addition, the muscles of the shoulder girdle, back, abdomen, etc. are involved. The lungs stretch, the pressure in them drops below the atmospheric pressure, and air enters the organ. When you exhale, the respiratory muscles relax, the chest volume decreases, the pressure in the pleural cavity increases, and due to this the lungs partially subside and the air is pushed out of them into the external environment. In deep expiration, the internal intercostal muscles, the muscles of the abdominal wall, which compress the internal organs, also contract. The latter begins to put pressure on the diaphragm and further acelerate the compression of the lungs. As a result, the volume of the chest cavity decreases more intensely than with a normal exhalation. Gas exchange in the lungs and tissues. Gas exchange in the lungs depends on the frequency of respiration, the level of oxygen and carbon dioxide concentration in the alveolar air and maintains the normal concentration of gases in the blood. In childhood, breathing is not quite rhythmical. The younger the child, the greater the respiratory rate, due to the fact that in children the need for oxygen is satisfied not at the expense of the depth, but at the expense of the frequency of breathing. The gas content in the inhaled and exhaled air is not the same. Inhaled air contains 20.94% of oxygen, about 79.03% of nitrogen, about 0.03% of carbon dioxide, a small amount of water vapor and inert gases; 16% of oxygen remains in exhaled air, the amount of carbon dioxide increases to 4%, the content of nitrogen and inert gases does not change, the amount of water vapor increases. Different content of oxygen and carbon dioxide in the inhaled and exhaled air explains the exchange of gases in the alveoli. Due to diffusion, oxygen 51

passes from the alveoli into the blood capillaries, and carbon dioxide – back. Each of these gases moves from the region with a higher concentration to the region with a lower concentration. Gas exchange in the tissues occurs based on the same principle. Oxygen from the capillaries, where its concentration is high, passes into the tissue fluid with a lower concentration. From the tissue fluid it penetrates into the cells and immediately enters into oxidation reactions, therefore there is practically no free oxygen in the cells. According to the same laws, carbon dioxide from the cells through the tissue fluid enters the capillaries, where it splits the unstable combination of oxygen with hemoglobin (oxyhemoglobin) and combines with hemoglobin, forming carbohemoglobin. Regulation of breathing. Changing the mode of the respiratory system, aimed at accurate and timely satisfaction of the body's need for oxygen is called the regulation of respiration. It carried out, as well as the regulation of other vegetative functions, in a nervous and humoral way. Nervous regulation of respiration is controlled by the respiratory center, located in the medulla, where every 4 seconds excitement occurs, due to which electrical impulses are transmitted to the respiratory muscles and cause their contractions. The spinal centers and the cerebral cortex are also involved in the regulation of respiration. The latter provides subtle mechanisms for adapting respiration to changes in environmental conditions. The cerebral cortex provides pre-start changes in respiration in athletes, an arbitrary change in rhythm and depth of breathing in humans. In the spinal cord, there are neurons, the axons of which innervate the diaphragm, intercostal muscles and abdominal muscles involved in the act of breathing. Humoral regulation of respiration occurs, firstly, due to the direct effect of blood CO2 on the respiratory center. Secondly, when the chemical composition of the blood changes (an increase in the concentration of carbon dioxide, an increase in the acidity of the blood, etc.), the receptors of the vessels are excited and impulses from them enter the respiratory center, respectively changing its work. Respiratory volumes. A person in a quiet state inhales and exhales about 0.5 liters of air (tidal volume). This volume characterizes the depth of breathing, however, after a quiet inhalation and exhalation, up to 1.5 liters of air remains in the lungs (reserve volume of inhalation and exhalation). The combination of respiratory and reserve volumes 52

of air is the vital capacity of the lungs. It reflects the largest amount of air that a person can exhale after taking the deepest breath. Vital capacity of the lungs in different people is not the same, its value depends on gender, age of a person, his physical development and is 3.5-4.0 l in adults. In seven-year-old boys, for example, it is 1.4 l, in girls – by 100 -300 ml less. It noted that the vital capacity of the lungs for every 5 cm of growth increases on average by 400 ml. During medical examinations, it is determined by a special device that is called a spirometer. Inspiration

Expiration

Thoracic cavity reduces

Thoracic cavity expands External intercostal muscles contract

External intercostal muscles relax

Diaphragm

Diaphragm contracts

Diaphragm relaxes

Figure 6. Inspiration and Expiration. Inspiration and expiration occur due to the expansion and contraction of the thoracic cavity, respectively.

The body is in contact with the external environment through the respiratory organs, therefore, to create conditions for the normal functioning of the respiratory system, it is necessary to maintain an optimal microclimate of classrooms. The formation of the microclimate of enclosed spaces depends on many factors: the characteristics of the layout of the rooms, the 53

properties of building materials, the climatic conditions of the area, the operating modes of ventilation and heating. The air temperature in the classroom should be 18-19 °C, in the gymnasium – 16-17 °C. The norm of the relative humidity of the air varies between 30-70% (optimum is 50-60%). The optimal air velocity in the class is 0.2-0.4 m/s. No less important in terms of the impact on the health and performance of schoolchildren is the control over the chemical composition of the air. The air of the premises constantly polluted by CO2 exhaled by people, decomposition products of sweat, sebaceous glands, organic substances contained in clothes, shoes, as well as chemicals released from polymeric materials (polyvinyl chloride, phenols, formaldehyde resins). In industrial premises, many technological processes are accompanied by the release of heat, moisture, and harmful substances in the form of vapors, gases, and dust. It has been shown that 3-5 minutes of airing is enough for the air in the classroom to be fully renewed. A number of school premises are equipped with artificial ventilation. Exhaust ventilation should be installed in the rooms of physics and chemistry, kitchens and toilet facilities of schools. Forced air ventilation, which provides approximately three air exchanges per hour, is to be present in gymnasiums and educational and labor workshops (ELW). Indoor ventilation is an extremely important and effective means of health protection and disease prevention. To prevent the penetration of pathogenic microorganisms into the respiratory tract, it is necessary to keep the room clean, to carry out wet cleaning, airing, and in contacting infected patients, gauze masks recommended. A number of viruses infect the upper respiratory tract and lungs, being spread by airborne droplets. These are pathogens of diphtheria, whooping cough, measles, rubella, influenza and respiretory diseases. The body does not have enough effective mechanisms to combat respiratory infections. Immunity develops for a period about a week, hence the average duration of the disease equals to a week. The main method of protection the body applies is the increase in the temperature, which is often mistakenly considered the main symptom of the disease. Currently, more than 200 types of viruses that cause infectious diseases are known. Influenza, especially type A, is more severe than the common cold. Its characteristic feature is a sudden onset of fever and chills. With the usual methods of treatment, the cold 54

passes in 2-5 days, and the full recovery of the body is obtained in 11.5 weeks. The active phase of the flu lasts about a week, but residual effects (weakness, muscle pain) may persist for another two-three weeks. The most common symptoms are rhinitis (runny nose), larynxgitis (inflammation of the larynx), pharyngitis (inflammation of the trachea), and bronchitis (inflammation of the bronchi). Often, once on the mucous membranes, viruses do not cause disease, but cooling of the body immediately leads to their development. Equally important for the respiratory system is sports, especially such types as running, swimming, skiing, rowing. People who start practicing sports in adolescence have a significantly enhanced lung capacity. Effect of smoking and alcohol on the respiratory system. Alcohol, much of which is excreted from the body through the lungs, damages the alveoli and bronchi, inhibits the respiratory center and contributes to the manifestation of lung diseases in a particularly severe form. Smoking causes great harm to the respiratory organs, since tobacco smoke contributes to the emergence of various diseases (bronchitis, pneumonia, asthma, etc.). Tobacco smoke irritates the mucous membrane of the larynx, bronchi, bronchioles, vocal cords, which leads to the restructuring of their epithelium. As a result, the protective function of the respiratory tract significantly reduces. About 800 g of tobacco tar, which accumulates in the alveoli, passes through the lungs per year. There is also a change in metabolic processes due to the radioactive elements of tobacco. In addition, smoking causes cough, aggravated in the morning, chronic inflammation of the airways, bronchitis, pulmonary emphysema, pneumonia, tuberculosis, cancer of various parts of the respiratory system. The voice becomes hoarse and rough. The primary cause of lung cancer in smokers is the presence of one of the most active polonium radioactive elements in tobacco tar. The degree of this danger can be judged from the following data: a person who smokes a pack of cigarettes a day receives a radiation dose 3.5 times the dose accepted by the international agreement on protection against radiation. It should be noted, that 90% of all established cases of lung cancer are diagnosed in smokers. Depending on the grade and processing, tobacco contains nicotine – 1-4%, carbohydrates – 2-20%, organic acids – 5-17%, proteins – 12%, and essential oils – 0.1-1.7%. One of the most poisonous 55

components of tobacco is nicotine. This substance, an alkaloid of chemical nature, was first isolated in its pure form in 1828 by scientists Posset and Reitman. One cigarette weighing 1g usually contains 1015 mg of nicotine, and a cigarette weighing 10g contains up to 150 mg of this substance. Apart from nicotine, tobacco leaves contain 11 more alkaloids, the most important of which are: nornicotine, nicotein, nicotimine, etc. All of them are similar to nicotine in structure and properties and therefore have similar names. Nicotine acts on the body in two phases. Initially, irritability and excitability of different systems and organs follow, and then this state is replaced by oppression. Nicotine in the first phase of its action excites the vasomotor and respiratory centers, and in the second phase inhibits them. At the same time, an increase in blood pressure occurs, which is caused by narrowing of peripheral vessels. In addition, carbon monoxide (CO) coming from cigarettes raises cholesterol in the blood and causes the development of atherosclerosis. It is estimated that the lethal dose of nicotine for a person is 1 mg per 1 kg of body weight (the whole pack contains one deadly dose of nicotine for an adult). According to the WHO, the overall death rate of smokers exceeds the death rate of non-smokers by 30-80%, with the most significant difference occurring at the age of 45-54 years, i.e. the most valuable age in terms of professional experience and creative activity. Passive smoking is no less harmful, especially for children, as for the neutralization of toxic substances of tobacco smoke the child's body must waist the vitamins and sulfur-containing amino acids necessary for the growth and development. The close connection of the formation of the respiratory system with the physical development and maturation of other body systems is noted. Intensive development of skeletal muscles at the age of 1216 years affects the nature of the age-related transformations of the adolescent respiratory system. In particular, adolescents with high growth rates often have a lag in the development of the respiratory organs. Outwardly, this manifests itself in the form of shortness of breath even in performing small physical exertion. Such children complain of fatigue, have low muscular performance, and avoid classes with intense exercise. For them, a gradual increase in physical training under the supervision of a physician is recommended. In contrast, in the adolescents involved in sports, the annual increase in growth is 56

less, and the functionality of the lungs is higher. In general, the development of the respiratory organs in the overwhelming majority of children bears the "imprints of civilization". Low motor activity limits the mobility of the chest. In this case, breathing is superficial, and its physiological value is low. It is necessary to teach children proper and deep breathing, which is a necessary condition for maintaining health, expanding the ability to adapt to physical exertion. Questions for self- control 1. What are the main sections of the respiratory system? 2. What are the functions of the upper airways? 3. What are the functions of the lower airways? 4. What is the essence and significance of breathing? 5. What are the stages of the breathing process? 6. What are the pulmonary volumes?

57

CHAPTER

6

AGE-RELATED ANATOMO-PHYSIOLOGICAL FEATURES OF THE DIGESTION SYSTEM. EXCHANGE OF SUBSTANCES AND ENERGY For the normal functioning of the body, a regular intake of food, representing a combination of organic and inorganic substances received by man from the environment and used by him to support life, is required. With food, a person receives vital substances (proteins, fats, carbohydrates, vitamins, mineral salts, water), which are used by the body to build and regenerate cells, tissues and replenish consumed energy. Digestion is mechanical and chemical (enzymatic) processing of food, in the course of which nutrients are consumed and absorbed in the digestive canal, and undigested residues and final decomposition products removed from the body. Chemical processing of food is carried out with the help of enzymes of digestive juices (saliva, gastric, pancreatic, intestinal juice, bile). Enzymes are proteinaceous substances that are secreted by the endocrine glands. They are active only at a certain acidity of the medium, temperature, and are capable of splitting strictly defined substances. For example, gastric juice enzymes are active in acidic environment; saliva enzymes are active in alkaline environment. All enzymes are divided into three groups: proteases, lipases, carbohydrates. Proteases (pepsin, trypsin) break down proteins into amino acids and are contained in gastric, pancreatic and intestinal juices. Lipases act on fats to form glycerin and fatty acids 58

and are part of the pancreatic and intestinal juices. Amylases break down carbohydrates into glucose and are present in saliva, pancreatic and intestinal juices. The structure and function of the digestive organs. The system of digestive organs consists of the digestive canal and digestive glands (salivary, pancreas, liver). The digestive canal is formed by the oral cavity, pharynx, esophagus, stomach, and intestine. The bones of the upper and lower jaws and muscles construct the oral cavity. Its upper boundary is formed by a hard and soft palate, the lower one is formed by the maxillary is hypoglossal muscles, on the sides there are the cheeks, and in the front part there are the gums with teeth and lips. The hard palate has a mucous membrane spliced with the periosteal. In its rear part, the hard palate passes into the soft palate, formed by muscles, covered with mucous membrane. The back section of the soft palate forms the uvula. In the process of swallowing, the muscles of the soft palate, contracting, separate the nasal part of the throat from the mouth. In the lateral folds of the soft palate, there are palatine tonsils (clusters of lymphoid tissue that perform a protective role). A human has six tonsils: two palatines, two tubes in the pharyngeal mucosa, lingual – in the mucosa of the tongue root, pharyngeal – in the pharyngeal mucosa. Due to them, the lymphoid pharyngeal ring is formed, which intercepts the pathogens that penetrate with food. The gums and teeth are located in the mouth (Figure 7). The tongue is a movable muscular organ formed by striated muscles, covered with a mucous membrane, supplied with vessels and nerves. In the tongue, the front free part (body) and rear part (root) are distinguished. In the mucous membrane of the tongue, there are threadlike, gutter shaped, mushroom shaped and leaf shaped papillae, which contain taste buds. The tongue is involved in the mechanical processing of food, mixing it and forming a food bolus, as well as in determining the taste and temperature of food. Taste receptors on the tip of the tongue perceive the sweet taste, the root of the tongue – bitter taste, the side surfaces – sour and salty taste. The tongue along with the lips and jaws is involved in the formation of speech. In the oral cavity, the ducts of three pairs of large salivary glands open: the parotid, sublingual, submandibular, and of many smaller ones. Saliva is the first alkalescent digestive juice that acts on food. The enzyme of saliva – amylase (ptyalin) breaks down starch to 59

maltose, and the enzyme maltase breaks it down to glucose. Saliva has a bactericidal property due to the enzyme lysozyme. The composition of saliva varies with the age of the person and in dependence on the type of food. The drier the food taken, the more viscous the saliva is. Sour and bitter substances secrete a significant amount of liquid saliva.

Parotid

Mouth

Sublingual Submandibular

Salivary glands

Pharynx Trachea Esophagus

Stomach Diaphragm

Liver (cut)

Spleen

Gallbladder Duodenum

Large intestine (transverse colon)

Common bile duct Pancreas

Small intestine

Cecum

Sigmoid colon

Appendix Rectum Anus

Figure 7. The digestive system.

There is practically no processing in the oral cavity, since here monomers are not formed (the smallest structural units of nutrients), the residence time of food is minimal. The exceptions are medicinal substances, alcohol and a small amount of carbohydrates. 60

One of the most important elements of the digestive system are teeth. In total, there are 32 teeth (incisors, canines, small and large indigenous). A type of bone tissue is dentin (the strongest tissue in the human body) that forms the teeth. Each tooth has a root, a cavity filled with loose connective tissue (pulp), a crown covered with enamel, a neck. Cutters serve to grab and bite off food. They have a chiselshaped crown and a single root. Fangs crush and tear food. The crown of a fang has two cutting edges, and the root is single and long. Small molars have two chewing tubercles on the crown, which serve to grind food. The roots of these teeth are solitary, but split at the ends. Large molars, unlike small ones, have three or more chewing tubercles. The upper ones have three root sprouts, the lower ones – two. In a child, they usually begin to cut through at the 6-7th month of life. These are milk teeth; there are only 20 of them. By the age of 1314, permanent ones replace them. From 20-22 years old, and sometimes later, large molar teeth called wisdom teeth, cut through. There are four of them. They are very fragile and do not participate in the act of chewing. The three roots of the wisdom tooth merge into one conical root. Tooth formula for permanent teeth has the following structure: 2.1.2.3 2.1.2.3 This means that on each half of the upper and lower dentition there are two incisors, one canine, two small molars and three large molars. The dental formula for milk teeth is: 2.1.0.2 2.1.0.2 On each half of the upper and lower dentition there are five teeth: two incisors, one canine, two molars (Figure 8). The most common dental diseases are caries and pulpitis. In caries, the integrity of the enamel covering the crown is broken, and a cavity appears in the tooth. Pulpitis is a disease accompanied by inflammation of the soft tissues in the center of the tooth. These diseases occur because of the activity of microorganisms, due to lack of fluorine or vitamins C and D. In addition, because of the relaxation of the muscles of the gums, a distortion of the elasticity of their blood vessels causes the disease called paradontosis. It caused by the lack of vitamin C. 61

Enamel

Dentin

Crown

Gingiva

Neck Pulp chamber (blood vessels & & nerves)

Root Cementum Jaw bone

Figure 8. A molar tooth.

In the oral cavity, the food that is ground by the teeth is moistened with saliva, and turned into a food bolus, which with the help of the muscles of the tongue is moved to the throat. Due to the reflex contraction of the muscles of the pharynx, an act of swallowing occurs and food enters the esophagus. At the same time, the epiglottis descends, closing the entrance to the larynx, and the soft palate rises, blocking the way to the nasopharynx. Esophagus. The wall of the esophagus, as well as other parts of the digestive canal, consists of three layers: the inner mucosa; the middle layer is the muscular layer and the outer one is the serous membrane. It is a cylindrical tube with a length of 22-30 cm, which has a slit that is like lumen at rest. In its length, the esophagus has three contractions. Food moves down the esophagus into the stomach due to the wave produced by contraction of the muscles of its wall. Liquid food moves along it for 1 sec., solid food – for 8-9 sec. The mucous membrane of the esophagus in children is rich in blood vessels, tender and easily vulnerable. Elastic tissue and mucous glands in the wall of the esophagus of children, are underdeveloped, 62

emit little mucus. This makes it difficult for insufficiently chewed food to pass through the esophagus in children of primary and secondary school age. Therefore, coarse food in their diet should occupy a small place. The stomach is an extended thick walled part of the alimentary canal, which lies in the abdominal cavity below the diaphragm. It consists of three parts – the upper (bottom), middle (body) and internal (pyloric region). In the stomach, there is a cardiac hole, which is the entrance, and the pylorus, which is the exit. The lower, convex edge of the stomach forms a large curvature of the stomach, and the upper concave one is small. The capacity of the stomach of an adult is 1.5-4 liters. In a newborn, its capacity is about 7 ml, by the end of the first week it is already 80 ml, the child eats this amount of milk at one time. By the age of seven, the stomach is shaped like that of an adult. In the gastric mucosa, there are glands that produce gastric juice. There are three types of cells in them: 1) The main cells that secrete the enzymes pepsin and chymosin; 2) Parietal cells emitting hydrochloric acid; 3) Additional cells producing mucoids and mucus substances that protect the membrane from mechanical and chemical effects. Glands of the stomach produce 1.5-2.5 liters of gastric juice per day. It is a colorless liquid containing hydrochloric acid (0.3-0.5%) and having an acid reaction (pH = 1.5-1.8). In an acidic environment, the enzyme pepsin breaks down proteins into the structural components of peptides, and chymosin inhibits milk protein. Proteins subjected to the preliminary action of proteases and the resulting fragments of protein molecules then are more easily broken down by proteases of pancreatic juice and small intestine. Adult gastric juice has a slight lipolytic activity, i.e. the ability to break down emulsified milk fats. This activity is important for the child during the period of milk feeding. Thanks to hydrochloric acid, denaturation and swelling of proteins occur, which contributes to their rapid cleavage, neutralization of microorganisms coming with food. The acidity of the gastric juice of the first months of life is low; it increases by the end of the first year and becomes normal by 7-12 years of life. In humans, outside the process of digestion, there is a continuous secretion of gastric juice. This is because a human receives food at 63

short intervals and therefore there is a constant stimulation of the activity of the gastric glands. Gastric secretion can be divided into three phases. The first phase begins with the irritation of the distant receptors of the eye, ear, nose, excited by the look and smell of food, the whole situation is associated with its reception. Unconditioned reflexes that occur when the receptors of the oral cavity and pharynx are irritated join them. Nerve influences trigger effects, i.e. abundant secretion of gastric juice, because of which the stomach is prepared in advance for meals. In the second phase, the secretion of gastric juice occurs, which is caused by unconditioned reflex effects due to food irritation of the mechanoreceptors of the stomach and humoral effects (the effect of the hormones gastrin, histamine). The third phase is called intestinal. During it, the effects from the intestine, transmitted by the nervous and humoral pathways, stimulate gastric secretion. For example, the products of hydrolysis of nutrients, especially proteins, cause the release of gastrin and histamine, and the products of hydrolysis of fat inhibit gastric secretion. Food in the stomach for 4-8 hours is subjected to both chemical and mechanical processing. Motor function is carried out by the contraction of the smooth muscles of the stomach. Thanks to them, pressure is maintained here, food moves with gastric juice. In the central part, the contents are not mixed, so the food taken at different times is located in the stomach in layers. Carbohydrate food lingers less in the stomach than protein. Oily food is evacuated with the lowest speed. Fluids begin to pass into the intestines immediately after they enter the stomach. In children of the first months of life, the evacuation of the contents of the stomach is delayed. When the baby is fed naturally, the stomach contents are evacuated faster than with artificial formula products. The level of the absorption in the stomach is small. Here, water and mineral salts dissolved in it, alcohol, glucose and a small amount of amino acids are absorbed. Small intestine. Further, digestion continues in the small intestine, the length of which is 5–7 m. We distinguish between the duodenum and the jejunum and ileum, where chemical processing of food and absorption of cleavage products occur, and mechanical mixing and movement of food into the large intestine are continued. In addition, 64

the endocrine function characteristic of the small intestine is the production of biologically active substances that stimulate the activity of enzymes. The mucous membrane contains numerous glands that produce intestinal juice, which includes more than 20 enzymes that act on all food substances and the products of their incomplete splitting. The mucosa of the small intestine is covered with numerous villi that increase its absorption surface. In the newborn, the small intestine has a length of 1.2 m, by the age of 2-3 it increases to 2.8 m, and by the age of 10, it reaches the length of the small intestine of an adult. The duodenal mucosa secretes a group of enzymes that act on proteins, fats, carbohydrates. In addition, pancreatic juice and liver bile come here. In an empty stomach, its contents have a slightly alkaline reaction (pH = 7.2-8.0). When the food bolus is soaked with intestinal juice, the action of the gastric enzyme pepsin is terminated and the food is exposed to pancreatic juice, bile and intestinal juice. Pancreas. It is a gland of mixed secretion, located behind the stomach at the level of the second lumbar vertebra. It has a lobular structure. In the gland, there is a head, body and tail. The bulk of the gland has an excretory function, releasing its secret through the excretory ducts into the duodenum. Its smaller part, in the form of pancreatic islets, belongs to the endocrine formations, secreting insulin into the blood. The juice produced by the gland contains enzymes that break down proteins (trypsin, chymotrypsin), fats (lipase), carbohydrates (amylase) and nucleic acids (nucleases). It releases 1.5-2.0 liters of juice per day, which has a weakly alkaline reaction (pH = 7.8-8.4) and is a colorless transparent liquid. The pancreas in a newborn has a length of 3-7 cm. It lies more obliquely, possess more mobility and is relatively bigger than in adults. It develops most actively up to 1 year and at 5-6 years. By 1315 years, it reaches the size of an adult and its full development is completed by 25-40 years. The pancreas already in newborn secrets a lot of juice, and its enhanced activity in early childhood makes up for the insufficient development of the gastric glands. With age, the amount of pancreatic juice increases, and its digestive power and the number of enzymes decrease. Liver. This is the largest gland of the human body, located in the right hypochondrium; its mass is up to 1.5 kg. In the liver, blood proteins, glycogen, fat- like substances, prothrombin, etc. are synthesized. 65

It serves as a depot of blood and glycogen, neutralizes organic products of decomposition of organic substances (toxic substances) in the blood. In the liver bile is formed, which is involved in the processes of digestion and absorption. It does not contain digestive enzymes, but activates pancreatic and intestinal juice enzymes, emulsifies fats, facilitates their breakdown and absorption. Bile enhances the intestinal motor activity and inhibits the development of putrefactive processes in it. The bile contains bile acids, pigments and cholesterol. Bile pigments are the products of hemoglobin breakdown. The main bile pigment is bilirubin; it has a red yellow color. Another pigment, biliverdin, is greenish in color and is contained in a small amount. Cholesterol is dissolved at the expense of bile acids. Bile accumulates in the gallbladder and then is secreted into the duodenum reflexively when food enters the stomach. The liver of a newborn is very large and occupies a large half of the abdominal cavity. In adults, the liver mass is 2-3% of the total mass, in a newborn this percentage is significantly higher – 4.0-4.5%. In children, the liver is very mobile and its position depends on the position of the body. The weight of the liver and the amount of secreted bile per unit of weight in children is much greater. However, it contains less acid and the regulation of carbohydrate and fat metabolism in young children is insufficient. Colon. It is represented by the cecum with the appendix, the ascending, transverse and descending colon and rectum. Its length is 1.52 m. The colon in its appearance differs from the small intestine. It has a larger diameter, special longitudinal muscle cords or ribbons, characteristic swellings, processes of the serous membrane, containing fat. In the colon, a small amount of juice has an alkaline reaction (pH = 8.5-9.0). Here an intensive absorption of water, the formation of fecal masses occur. In addition, glucose, amino acids and some other easily absorbed substances are supplied in small quantities. In the colon numerous microorganisms (up to tens of billions per 1 kg of content) live, the value of which is quite significant. They are involved in the decomposition of undigested food residues and components of digestive secretions, the synthesis of vitamins K and vitamins of group B, enzymes and other physiologically active substances. Normal micro flora suppresses pathogens and prevents infection of the body. Violation of the normal micro flora in diseases or because of 66

prolonged administration of antibiotics, rapid reproduction in the intestines of yeast, staphylococcus and other microorganisms occurs. The cellulose arriving with vegetables and fruit, in a human body is used approximately by 40%. Products of its hydrolysis are absorbed in the large intestine. The enzymes of the bacteria of the latter break down the fibers. Up to 3 years the small and large intestine develops evenly, then the large intestine begins to develop faster. With the growth of the child, intestinal subsidence occurs, especially where the small intestine enters the fat one. The main function of the intestine is absorption. The process of absorption is a transition (diffusion) of the components of nutrients from the alimentary canal into the blood and lymph. Proteins are absorbed as amino acids, carbohydrates as glucose, and fats as glycerol and fatty acids. The process of absorption of nutrients is promoted by the presence of villi. Their number per one mm2 reaches 20-40, and their height is about 1mm, which significantly increases the area of contact of nutrients with the intestinal mucosa. They have a complex structure: the top is covered with epithelium, and inside they have blood and lymphatic vessels and muscle cells. The latter, contracting, work as a pump that injects the liquid contents of the intestinal cavity into the blood and lymph. The main absorption occurs in the small intestine, with the exception of plant fiber, which is absorbed in the large intestine. The process of digestion that occurs in stages in different parts of the digestive tract is under the constant control of the nervous and humoral mechanisms. I. P. Pavlov, who proved that the secretion of Saliva and gastric juice occurs reflexively and is an unconditioned food reflex, studied the importance of the central nervous system in the regulation of digestion. This process is mainly associated with direct irritation of food receptors in the mouth, esophagus, and stomach. The excitation generated in the receptors along the sensory nerves is transmitted to the medulla, where it is analyzed, the response impulse is sent along the centrifugal nerves to the working organs, and the separation of saliva, gastric juice, etc. occurs. With the help of the visual, auditory analyzers of the external signs of food, conditioned reflexes can also appear. 67

Humoral regulation is caused by the secretion by the gastric mucosa of hormone gastrin into the blood, which stimulates the secretion of gastric juice, biliary excretion, regulates the motor activity of the stomach and intestines. In addition, hormones of the anterior pituitary, adrenal cortex affect the synthesis of digestive enzymes, the processes of absorption and intestinal motility. Age features of the digestive system. The most significant morphological and functional differences between the digestive organs of an adult and a child are observed only in the first years of postnatal development. The functional activity of the salivary glands manifests with the appearance of milk teeth (from 5-6 months). A particularly significant increase in salivation occurs at the end of the first year of life. During the first two years, the formation of milk teeth is intensive. At the age of 2-2.5 years, the child already has 20 teeth and can eat relatively coarse food that requires chewing. In subsequent years, starting with 5-6 years, permanent teeth gradually replace the milk teeth. In the first years of postnatal development, the formation of other digestive organs is intensive: of the esophagus, stomach, small and large intestines, liver and pancreas. Their size, shape and functional activity change. Thus, the volume of the stomach from birth to 1 year increases 10 times. The shape of the stomach in a newborn is round, after 1.5 years, the stomach becomes pear-shaped, and from 6-7 years, its shape is no different from that of adults. Significantly changes the structure of the muscle layer and the mucous membrane of the stomach. In young children, there is a weak development of the muscles and elastic elements of the stomach. The stomach glands in the first years of a child's life are still underdeveloped and scarce, although they are capable of secreting gastric juice, in which the content of hydrochloric acid and the quantity and functional activity of enzymes are much lower than in adults. Thus, the number of enzymes that break down proteins increases from 1.5 to 3 years, then at 5-6 years and at school age up to 12-14 years. The content of hydrochloric acid increases by 15-16 years. The low concentration of hydrochloric acid causes weak bactericidal properties of gastric juice in children up to 6-7 years, which contributes to a higher susceptibility of children of this age to gastrointestinal infections. 68

In the process of development of children and adolescents, the activity of the enzymes changes significantly. In the first year of life, the activity of the enzyme, called chymosin, acting on milk proteins, changes especially significantly. In a child of 1-2 months, its activity in arbitrary units is 16-32, and at 1 year it can reach 500 units, in adults this enzyme completely loses its value in digestion. With age, the activity of other enzymes of gastric juice also increases, and in senior school age, it reaches the level of an adult. It should be noted, that in children under 10 years of age, the processes of absorption are active in the stomach, while in adults these processes are carried out mainly in the small intestine. The pancreas develops most intensively up to 1 year and at 5-6 years. According to its morphological and functional parameters, it reaches the level of an adult by the end of adolescence (at 11-13 years old, its morphological development is completed, and at 15-16 years of age – functional development). Similar rates of morphological functional development are observed in the liver and all parts of the intestine. Humoral regulation is caused by the secretion of hormone gastrin by the gastric mucosa into the blood, which stimulates the secretion of gastric juice, biliary excretion, regulates the motor activity of the stomach and intestines. In addition, hormones of the anterior pituitary, adrenal cortex affect the synthesis of digestive enzymes, the processes of absorption and intestinal motility. Age features of the digestive system. The most significant morphological and functional differences between the digestive organs of an adult and a child are observed only in the first years of postnatal development. The functional activity of the salivary glands manifests with the appearance of milk teeth (from 5-6 months). A particularly significant increase in salivation occurs at the end of the first year of life. During the first two years, the formation of milk teeth is intensive. At the age of 2-2.5 years, the child already has 20 teeth and can eat relatively coarse food that requires chewing. In subsequent years, starting from 5-6 years, permanent teeth gradually replace the milk teeth. In the first years of postnatal development, the formation of other digestive organs is intensive: of the esophagus, stomach, small and large intestines, liver and pancreas. Their size, shape and functional activity change. Thus, the volume of the stomach from birth to 1 year increases 10 times. The shape of the 69

stomach in a newborn is round, after 1.5 years, the stomach becomes pear-shaped, and from 6-7 years, its shape is no different from that of adults. Significantly changes the structure of the muscle layer and the mucous membrane of the stomach. In young children, there is a weak development of the muscles and elastic elements of the stomach. The stomach glands in the first years of a child's life are still underdoveloped and scarce, although they are capable of secreting gastric juice, in which the content of hydrochloric acid and the quantity and functional activity of enzymes are much lower than in adults. Thus, the number of enzymes that break down proteins increases from 1.5 to 3 years, then at 5-6 years and at school age up to 12-14 years. The content of hydrochloric acid increases by 15-16 years. The low concentration of hydrochloric acid causes weak bactericidal properties of gastric juice in children up to 6-7 years old, which contributes to a higher susceptibility of children of this age to gastrointestinal infections. In the process of development of children and adolescents, the activity of the enzymes changes significantly. In the first year of life, the activity of the enzyme, called chymosin, acting on milk proteins, changes especially significantly. In a child of 1-2 months, its activity in arbitrary units is 16-32, and at 1 year it can reach 500 units, in adults this enzyme completely loses its value in digestion. With age, the activity of other enzymes of gastric juice also increases, and in senior school age, it reaches the level of an adult. It should be noted, that in children under 10 years of age, the processes of absorption are active in the stomach, while in adults these processes are carried out mainly in the small intestine. The pancreas develops most intensively up to 1 year and at 5-6 years. According to its morphological and functional parameters, it reaches the level of an adult by the end of adolescence (at 11-13 years old, its morphological development is completed, and at 15-16 years of age – functional development). Similar rates of morphological functional development are observed in the liver and all parts of the intestine. Thus, the development of the digestive organs goes in parallel with the general physical development of children and adolescents. The most intensive growth and functional development of the digestive organs is observed during the 1st year of postnatal life, in preschool age and in adolescence, when the digestive organs in their 70

morphological and functional properties approach the level of an adult. In addition, in the process of life in children and adolescents, conditioned alimentary reflexes, in particular, reflexes connected with mealtime, are easily developed. In this regard, it is important to teach children strictly adhere to the diet. Important for normal digestion is the observance of "food aesthetics". The concept of metabolism and energy. Metabolism and energy is the entry into the body from the external environment of various substances, their absorption and alteration, the release of the formed decay products. Metabolism is inseparable from the transformation of energy. Organic matter coming from food is used as a building material of the body, as well as energy resources. After a series of chemical transformations, their own substances specific for the given organism and for this organ are synthesized from the substances received from food, from which the cellular structures are built. The energy role of nutrients is that the energy released during the splitting and oxidation of them to the final products is used. Energy in the human body is used to maintain body temperature at a certain level, as well as for the synthesis of cell components during the growth of the body and to replace worn parts. It is necessary for the activity of all systems and organs, even if a person is at rest. The amount of food that a person eats in his life is many times greater than his own weight, which indicates a high rate of metabolic processes in the body. Metabolism in children is higher than that in adults, and is not constant even within the same age group, as it is closely associated with the processes of growth and development of the body and the state of the nervous system. There are periods of the metabolism increasing and slowing down, which is associated with the acceleration and deceleration of the process of growth and development in different seasons of the year. More intensive metabolism is observed in newborns. In younger schoolchildren, it is much lower, but during puberty, it rises greatly. The metabolism in adults varies with physical exertion, as well as the state of health. Protein metabolism. In the body, proteins perform various functions. Being the main material from which the cells of our body are built, proteins perform a construction role. Enzymes and hormones have a protein nature. The first ones are able to change the rate of chemical transformations in the process of metabolism; the second ones 71

provide humoral regulation of body functions. Contractile proteins – actin and myosin – perform all types of motor reactions in the body. Some proteins perform a transport function, for example, hemoglobin. Proteins perform an immune function, as antibodies produced in the body are proteins. Their splitting, as well as absorption, and excretion from the body, occurs continuously. Therefore, continuous replenishment of proteins in the body and, especially, in the process of development is required. The structure of simple proteins includes only four chemical elements: oxygen, hydrogen, carbon and nitrogen. The composition of complex proteins (e.g., brain proteins) also includes sulfur, phosphorus, iron, etc. The intensity of protein metabolism in the body is determined by the amount of nitrogen supplied and released from the body, since protein, in contrast to other organic substances of the human body, contains nitrogen in its composition. The ratio of the amount of nitrogen, received and excreted from the body, determines the nitrogen balance. If the amount of nitrogen entering the body is greater than that removed, then we speak of a positive nitrogen balance. Such a predominance of protein synthesis over decay is observed in childhood (from birth until the end of the growth of the body). If the amount of nitrogen released is greater than that received amount, that is, protein breakdown in the body prevails over synthesis, there is a negative nitrogen balance that occurs in some diseases, in starvation, and in the use of defective proteins. Proteins are polymeric compounds consisting of monomers – amino acids. Only 20 amino acids are known, of which all protein compounds that make up the human body are built. Both the number of constituents of protein molecules of amino acids, and their sequence determine the specificity of proteins. Of all the amino acids, only eight are essential for humans. These include tryptophan, leucine, isoleucine, valine, threonine, lysine, methionine, and phenylalanine. Histidine is also required for a growing body. Proteins containing the entire necessary set of amino acids in such ratios that ensure normal protein synthesis are biologically valuable proteins. On the contrary, proteins that do not contain certain amino acids will be defective. For example, gelatin (no tryptophan, etc.), corn protein – zein (little tryptophan and lysine), gliding wheat protein 72

(little lysine) and some other proteins are inferior. The highest biological activity of proteins is found in meat, eggs, fish, caviar, milk. In this regard, the food must have at least 30% of animal protein in its composition. The lack of any of the essential amino acids in food (the rest can be synthesized in the body) causes serious disruptions in the body's vital functions, especially in the growing body of children and adolescents. Protein starvation leads to a delay, and then to a complete cessation of growth and physical development. The child becomes sluggish; there is a sharp weight loss, abundant swelling, diarrhea, inflammation of the skin, anemia, a decrease in the body's resistance to infectious diseases, etc. Regulation of protein metabolism is nervous and humoral. Nervous impulses are controlled by the hypothalamic region of the diencephalon. Humoral regulation is realized by the somatotropic hormone of the pituitary and thyroid hormones thyroxin and triiodothyronine, which stimulate protein synthesis. The hormones of the adrenal cortex – hydrocortisone, corticosterone increase the breakdown of proteins in tissues, especially in muscles and lymphoid tissue, and in the liver, they stimulate fat metabolism. Fat metabolism. Fats in the body are used mainly as an energy material. Their participation in the construction of organs and systems, that is, the plastic function, is very insignificant. One gram of fat when splitting gives 9.3 kcal of energy. Most of the fat is in adipose tissues and is the energy reserve. A smaller part of the fat goes to build new cell membrane structures and to replace the old ones. Some cells of the body are able to accumulate fat in large quantities, thus fulfilling the role of thermal and mechanical isolation in the body, i.e. protective functions. Any fat absorbed by the intestines mainly enters the lymph and in small amounts the blood. Fats include fats and fat-like substances (lipids). Lipids are formed by the compound glycerin alcohol and fatty acids. Lipids include phosphatides and sterols. Despite the fact that the specificity of fat is less pronounced than the specificity of proteins, a person has a relative constancy of the composition and properties of fat. This is due to the presence of fatty acids in them. The latter are divided into saturated and unsaturated ones. 73

Saturated fatty acids are found in animal fats, as well as in coconut and palm oil. They are usually in a solid state at room temperature and usually harden when cooled. Milk fats do not harden, because they are homogenized, that is, subjected to a process leading to their dispersion. Unsaturated fatty acids are mainly found in vegetable fats that remain liquid both at room temperature and during cooling. The biological value of fats is determined by the fact that some fatty acids cannot be formed in the body and are indispensable. These include linoleic, linolenic acid, and arachidonic acids. Linoleic and linolenic acids are found in vegetable oils, especially in olive, sunflower and hemp oil. Arachidonic acid is found in chicken, goose and lard. With their deficiency, pathological changes in the vascular wall develop leading to a serious disease – atherosclerosis. Disorders of sexual function may also occur. In the human diet, vegetable fats should prevail. After 40 years, animal fats should be virtually eliminated from the diet. Hard fats of animal origin are harmful to the body. They are embedded in the cell membrane, making it impermeable to various substances, causing the cell to age. Excessive body fat of any kind contributes to its conversion to glycogen in the liver and muscles, leads to acidosis (increased acidity of blood and other fluids that make up the internal environment of the body), reduces appetite, leads to obesity, and sometimes causes gastrointestinal disorders. In children, the body requires more energy material. For example, in the first year of life a child should receive 7 g of fat per 1 kg of body weight per day, by the age of four – up to 3.5-4 g, at the younger school age – 2.5-2 g, at 10-12 years – 1.5 g, for an adult 1 g per kilogram of weight is required. Great importance in the food for babies should be attributed to the quality of fat. In general, it is better for children to use dairy fats, and in the first year of life, breast milk fats are needed, as they are assimilated by 94-98%, and those of artificial feeding formulas only by 85%. You should not deprive children of vegetable fats, unsaturated fatty acids that stimulate growth, normalize skin function, and reduce the level of cholesterol in the blood. Regulation of fat metabolism is nervous and humoral. Parasympathetic nerves contribute to deposition of fat and sympathetic ones – on the contrary. Nervous system impulses are controlled by the hypothalamic region of the diencephalon (as to fat deposition and slimming). Humoral regulation is realized by the somatotropic hormone of 74

the pituitary gland, hormones of the adrenal medulla – adrenaline and noradrenaline, and the hormone of the thyroid gland – thyroxin, which has a fat- mobilizing effect. Glucocorticoids of the adrenal cortex, as well as pancreatic insulin have an inhibitory effect on fat mobilization. Carbohydrate metabolism. Carbohydrates are the main sources of energy (1 g emit 4.1 kcal) and construction material (construction of cell membranes, connective tissues) in the body. They are strongly split in the digestive tract and absorbed by 90-98%. Carbohydrates in the body are broken down to simple sugars – glucose, fructose, galactose, etc. Their composition, like the composition of fats, includes three chemical elements: oxygen, hydrogen, and carbon. The same chemical composition of fats and carbohydrates allows the body in an excess of carbohydrates to build fats from them, and vice versa, if necessary, carbohydrates are easily formed from fats in the body. The need for carbohydrates per day is as follows: at the age of 13 years – 193 g, at 8-13 – 370 g, at 14-17 – 470 g, which is close to the normal value for an adult (500 g). The level of glucose in the blood of younger schoolchildren is 0.08-0.1%, that is, it is almost equal to the norm of an adult. However, a large amount of sugar in food increases its content in the blood by 50-70 and even 100%. This is a so-called alimentary (food) increase, or glycaemia, which in young children does not cause concern due to increased carbohydrate metabolism. Glycaemia in adults in the range of 0.15-0.16% causes the appearance of sugar in the urine. In some cases, a pathological increase in the concentration of carbohydrates in the blood is possible; it may be accompanied by enhanced excretion of sugar in the urine. This disease, is called diabetes mellitus, it is associated with impaired pancreatic intrasecretory function. With low blood sugar (less than 0.1%), the glycogen present in the liver and muscles is broken down to glucose and enters the blood; the formation of glucose is also possible from proteins and fats. Pathological decrease in glucose to 0.05% is life threatening, fainting occurs (insulin shock), which is also associated with dysfunction of the pancreas. Children (including those of school age) should receive with food not only easily digestible carbohydrates: glucose, sugar, starch, but also non-cleavable ones – fibers and pectins. If the former are needed as a source of energy, fibers are needed to strengthen the teeth and the entire masticatory apparatus, and as an irritant to the intestines, a 75

stimulator of peristalsis. Fibers regulate the activity of normal microflora in the intestines, helps to eliminate cholesterol. Lack of fibers contributes to the development of obesity, and in adulthood, cardiovascular diseases, intestinal cancer and other disorders. Another indigestible sugar is pectin, which is abundant in all fruits and vegetables, but most of all in the peel of apples and citrus fruit. It also contributes to the suppression of putrefactive microflora in the human intestine, the elimination of cholesterol from the body. Fibers with pectin are also called dietary fibers. The optimal content is 10-15 g a day. This need is easily covered with a whole grain bread, vegetables and fruits. A lot of them are present in dry fruits and vegetables, raisins and prunes. Regulation of carbohydrate metabolism may be nervous and humoral. Nervous system impulses are controlled by the hypothalamic region of the diencephalon. Humoral regulation realized by the pituitary growth hormone and thyroid hormones – triiodothyronine and thyroxin, glucagon, produced by the pancreas, and adrenaline – the hormone of the adrenal medulla, and hormones of the cortical layer of the adrenal gland – glucocorticoids that increase blood sugar levels. Insulin is the only hormone that causes a decrease in blood glucose levels. Water metabolism. Water and other minerals (salts, acids, alkalis) used by the body are part of all its tissues. Water and mineral salts dissolved in it take an active part in the synthesis of substances in the process of tissue growth. The total amount of water in the body depends on age, gender and body weight. On average, the human body contains about 61% of water. The water content in the child's body is much higher, especially at the early stages of development. In the body of the newborn water content makes from 70 to 80%. Most of the water is found in blood – 92%, in the muscles – 70%, in the internal organs – 76-86%. The least water content is in the bones – it is 22%, and in the adipose tissue – 30%. A higher water content in the body of children, obviously, is associated with a greater intensity of metabolic reactions associated with rapid growth and development. The overall need for water for children and adolescents increases as the body grows. If a one-year-old child needs about 800 ml of water per day, a 4 year-old one – 1000 ml, at 7-10 years the need is 1350 ml, at 11-14 years – 1500 ml. The human need for water at ordinary temperatures is 2-2.5 liters. 76

Restriction of water intake distorts the intracellular metabolism in the body, changes the color of the skin and visible mucous membranes, and causes thirst. It is best to quench your thirst with purified fresh water or natural juices. The vitamins and minerals contained in the latter make them a useful substitute for commercial soft drinks, which contain only sugar, water, preservatives and artificial additives. It is recommended to use special filters for water purification. The presence of salts in the body, their retention and excretion depend not only on food intake, but also on their content in drinking water. Be aware that boiling not in all cases causes precipitation of salts and reduces water hardness. The use of natural mineral water is one of the oldest methods of treating a number of diseases, but it should only be consumed on a doctor's prescription in strictly defined quantities. Its frequent use leads to a distortion of salt metabolism. Carbon dioxide, which is contained in carbonated beverages, causes irritation of the gastric mucosa and excessive secretion. In hot weather, a good remedy for quenching thirst is tea, which increases salivation and moistens dry mouth. You can also add to the water some fruit and vegetable juices or extracts. Regulation of water metabolism is carried out by neuro-reflex and humoral mechanisms. The first one is implemented by the nerve center, which is located in the intermediate brain, more precisely, in the hypothalamus. The second one is carried out using the following hormones: antidiuretic (pituitary hormone), mineralocorticoid (adrenal hormones). The value of vitamins. Vitamins are biologically active substances of various chemical nature, which in small quantities have a strong effect on metabolism. Insufficient intake of vitamins causes hypovitaminosis, but vitamin deficiencies are just as unfavorable for the body as their excess – hypervitaminosis. Vitamins accelerate biochemical reactions in the body, increase the activity of hormones and enzymes, and are involved in the formation of digestive enzymes. They are used to increase the body's resistance to infectious diseases, environmental factors. When organizing meals for schoolchildren, it is necessary to ensure that food contains sufficient amounts of vitamins and, above all, natural foods that are rich in vegetables, berries, and fruits throughhout the year. 77

Currently, more than 40 vitamins are known; some of them dissolve in water (B, C, P), others – in fats (A, D, E, K, F). During a prolonged storage of products, vitamins are lost. Thus, during 2 months of storage, potatoes lose half of vitamin C content; diffuse sunlight destroys up to 64% of milk vitamins within 5-6 minutes, and in the first minutes of cooking most of the vitamins are destroyed. Most fresh fruit almost never loses vitamin C, beta-carotene and other nutrients. While vegetables can lose about a quarter of vitamin C after being refrigerated, most fruits retain this vitamin for 7-10 weeks. In the biochemical method of fermentation of vegetables without a large amount of sodium chloride, a partial preservation of vitamin C is achieved, even for several months. To preserve vitamins, do not cut fresh vegetables in advance, because exposure to air destroys vitamin A and C, and light reduces the content of riboflavin and vitamin K. Steaming of vegetables gives them softness without loss of freshness, and saves more vitamins and minerals compared to frying. Use a steamer or other container with a tight lid. Boil vegetables better in a small amount of water, because water removes nutrients. To save more vitamin C, immerse the vegetables in boiling water. Since the skin of vegetables such as tomatoes, cucumbers and sweet peppers contain fiber, and the vitamins are stored directly at its surface, it is better not to peel them before eating. The same applies to fruit. For example, a peeled apple loses up to 25% of vitamin C. One of the most important sources of vitamins D, E, of group B are cereals. However, much of them are lost in the process of milling the flour. Since many of us consume cereals mainly in the form of bread, the easiest way to get the most out of grain products is to eat whole wheat or oatmeal bread instead of white bread. Minerals in the body play versatile and important functions. They determine the structure and functions of many enzymatic systems and processes, ensure the normal course of certain important physiological processes, take part in plastic processes and the construction of tissues, especially bone tissue. The balance of mineral salts in the body is influenced by the age and individual characteristics of children in different periods of the year. If an adult and healthy body takes an excess amount of mineral salts, they can be deposited in reserve. Thus, sodium chloride is deposited in the subcutaneous tissue, iron salts in – the liver, calcium – in 78

the bones, and potassium – in the muscles. With a deficit of these salts, they enter the organs from the depot. The sources of minerals are milk, eggs, meat, fruit and vegetables. The kidneys, sweat glands and intestines excrete minerals. Mineral salts are contained in food in sufficient quantities to support vital activity. Only sodium chloride is administered additionnally. However, a growing body requires more mineral salts. They are necessary for the growth of tissues and organs, for example, the skeletal system. Additionally, it is necessary to introduce salts of potassium, sodium, magnesium, chlorine and phosphorus. The same salts are also necessary for the developing fetus during pregnancy. Energy metabolism. The energy role of nutrients is that the energy released during splitting and oxidation of them to the final products is used. In the process of metabolism, energy is converted: the potential energy of organic compounds from food is converted into thermal, mechanical and electrical energy. The result of energy processes is heat generation, so the energy formed in the body can be expressed in calories and joules. The calorie content of food is its ability to release energy. With a long-term shortage of energetically valuable food, the body spends not only reserve carbohydrates and fats, but also proteins, which primarily leads to a decrease in skeletal muscle mass. As a result, there is a general weakening of the body. Basal metabolism is the minimum amount of energy a person needs to maintain life in a state of complete rest. Basal metabolism depends on age, on total body weight, on external living conditions and individual characteristics of a person. In men, physical manual workers who do not require significant energy expenditure, the average daily energy metabolism is equal to 2750-3000 kcal, for women of the same group, 2350-2550 kcal. For people of mental labor, energy consumption will be somewhat lower: 2550-2800 kcal for men and 2200-2400 kcal for women. In children, the basal metabolic rate is significantly higher than in adults. Between the ages of 20 and 40, it remains at a constant level. In old age, it decreases. The regulation of energy metabolism is carried out by the conditioned-reflex way with the participation of the cerebral cortex centers and the hypothalamic region of the diencephalon. A special role is played by humoral regulation, due to the secretion of thyroid

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hormones. These are thyroxin and triiodothyronine, and the hormone of the adrenal medulla is adrenaline. Basics of nutrition. It is important to remember that properly organized nutrition is a prerequisite for a normal and healthy life, and for children and adolescents rational nutrition is a necessary condition for their physical and mental development. Neglecting food is as harmful as excessive use. Excess protein in the body has a negative effect on it. Most sensitive to it are small children and the elderly. Kidney and liver are particularly affected, they increase in size and structural changes occur in them. A long-term excess use of proteins leads to over-excitation of the nervous system. If you immediately after feeding with breast milk switch the baby to food products that contain large amounts of protein – meat, cottage cheese, eggs, it negatively affects the child is accelerates its development, promotes the development of kidney and liver disease, and slows down mental development. During heat treatment, the tertiary structure of the protein is destroyed and after that, the proteins are better exposed to the action of digestive juices and better absorbed. However, prolonged heat treatment, for example, roasting, leads to the interaction of proteins with carbohydrates, resulting in the formation of substances that are not absorbed in the body. In fried meat, a number of harmful nitrogencontaining compounds are formed, including those with carcinogenic properties. The same thing happens when products are smoked. It has been established that for the body food without heat treatment is optimal. When boiled food is ingested, food leukocytosis is observed, a large number of white blood cells are sent to the intestinal walls, as in the case when some kind of damage is observed. The body reacts to boiled food, as to the invasion of something hostile. Being repeated several times a day, such a reaction exhausts the body. To prevent food leukocytosis and its consequences, it is recommended doing a deceptive maneuver: start a meal with a raw snack and then eat boiled food. There are several golden rules of nutrition. First, you cannot leave cooked food even for several hours and hope it would still be fresh. Immediately the processes of fermentation and rotting start. The next rule concerns raw food. It is recommended to use as many fresh vegetables and fruit as possible. Particularly useful are wild plants for 80

preventing obesity, hypertension, and atherosclerosis. However, if you are slim and easily excitable, it is better to consume boiled vegetables. Thirdly, remember of the seasonality of food. In spring and summer, you need to increase the amount of vegetable products, in winter you should eat food products rich in proteins. Also important are the diversity, alternation of food products and dietary restrictions. Food compatibility. In case of incompatible products, increased fermentation, rotting and intoxication with harmful substances may develop. It is established that the combination of fatty and starchy food products is unfavorable for the body. Starchy vegetables (potatoes, carrots, beets), protein products (meat, eggs, dairy products, nuts, legumes), cereals and bakery products are not compatible with each other, but are compatible with green vegetables consumed raw (cucumbers, radishes, onions, garlic, sorrel), salads, cabbage. There is a theory about nutrition, according to which you need to eat separately proteins and carbohydrates, proteins and fats, proteins and sugars, proteins and acids, acids and starch. To prevent obesity and clean the body, it is advisable to use fasting days. The menu in these days consists of monotonous non-nutritious food, and they are repeated once in 6-10 days. Long – term fasting is carried out only under the supervision of a physician (for 4-5 days). After it, you cannot eat salt, meat, fish, eggs, mushrooms. Energy metabolism in children and adolescents. The body's metabolism is closely related to the transformation of energy. The amount of energy produced in the body can be determined by direct and indirect calorimetry. One of the most important indicators of the intensity of metabolic processes in the body is the amount of basal metabolic rate, which refers to the level of exchange reactions at room temperature and in complete functional rest. The basal metabolic rate depends on age, gender and weight. On average, the basal metabolic rate for men is 7140-7560 kJ per day, and for women – 6430-6800 kJ. The intensity of metabolic reactions in children in terms of 1 kg of body weight or one m2 of its surface is much higher than in adults, although the absolute values are less. So, for boys of 8 years, the basal metabolic rate in terms of 1 m2 of surface is 6190 kJ, and for girls – 5110 kJ. Further, with age, the basal metabolic rate decreases and in boys of 15 years it is 4800 kJ, in girls – 4480 kJ. 81

If you know the energy expenditure of the body, it is possible to make an optimal diet so that the amount of energy coming from food completely covers the energy expenditure of the body. For children and adolescents, the composition of food is particularly important, since the child's body needs a certain amount of proteins, fats, carbohydrates, mineral salts, water and vitamins for normal development and growth. It is important to remember that for children and adolescents a normal diet is a necessary condition for their physical and mental development. Neglecting food is as harmful as overeating. Questions for self-control 1. What are the main divisions distinguished in the digestive system? 2. What are the age characteristics of the structure and functioning of the following parts of the digestive system: oral cavity, pharynx, esophagus, stomach, small and large intestines? 3. What are the age features of the structure and functioning of the digestive glands (liver, pancreas)? 4. At what age does the development of the gastrointestinal tract end? 5. What are the age-specific features of the metabolism of fats and carbohydrates? 6. What are the features of protein metabolism in a child? 7. What is the need for water for children and adolescents and how should it be satisfied?

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CHAPTER

7

PHYSIOLOGY OF THE EXCRETORY SYSTEM AND AGE FEATURES In the process of metabolism in the body decomposition products are formed. Accumulating, they disturb the constancy of the internal environment of the body and impede its activity. Carbon dioxide, water, and some volatile substances are removed from the body through the lungs. The intestine eliminates undigested food residues, calcium salts, bile pigments, partly water, and some other substances. Sweat glands remove 5-10% of all products of metabolism (water, salt, some amino acids, urea, uric acid, etc.). The main role in the excretory processes belongs to the kidneys, which remove from the body about 75% of the final metabolic products (ammonia, urea, uric acid, foreign and toxic substances formed in the body or taken in the form of drugs, etc.). The kidneys, removing excess water and mineral salts from the body, are involved in the regulation of the osmotic pressure of the blood. Elimination is the process of removal from the body of products of life, resulting from the decomposition of organic substances (carbon dioxide, water, urea, uric acid, salt, etc.). With the accumulation of these substances in the tissues, there is a danger of poisoning and death. The structure and age characteristics of the excretory system. The urinary system combines urinary and genital organs. They are closely related to each other in their development and, in addition, their excretory ducts are connected either into one large urinary tube (the urethra in men), or open into one common space (vestibule of the 83

vagina in women). Urinary organs include paired organs – the kidneys and urinary tract. The kidneys are paired organs of the bean-shaped form, about 10 cm long, located on both sides of the spine at the level of the XII thoracic and II lumbar vertebrae on the posterior wall of the abdominal cavity. The right kidney lies 2-3 cm below the left one. On the inner, concave side of the kidney, there is a funnel-shaped cavity (renal pelvis), from which the ureter departs. Blood and lymph vessels, nerves, forming the so-called kidney gate, also come here. In the kidney, there are external (cortical) and internal (medulla) layers. The cortical layer is located on the periphery of the kidney and, entering as columns in the medulla, divides it into 15-20 renal pyramids. Each base of the pyramid faces outward, and the tip – toward the renal pelvis. The cortical substance has a red-brown color, and the brain is somewhat lighter. The structural and functional unit of the kidney is the nephron (Figure 9). Hepatic veins

Diaphragm

Interior vena cava

Adrenal gland

Abdominal aorta

Right kidney

Renal artery

Right ureter

Common iliac vein

Renal vein

Common iliac artery Internal liac vein Urinary bladder

Internal iliac artery External iliac artery

Prostate gland

External iliac artery

Urethra

Figure 9. Urinary system, showing blood vessels

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The nephron begins in the cortical substance of the kidney with a small capsule having the shape of a double – walled cup, inside of which there is a glomerulus of blood capillaries. Between the walls of the capsule, the urinary tubule of the nephron begins from a cavity. It twists and then enters the medulla, receiving the name of a convoluted tubule of the first order. In the medulla, the urinary tubule straightens, forms a loop and returns to the cortical layer. Here it twists again, forming a twisted second-order tubule, which flows into the outflow duct or into the collecting tube. The latter, merging, form common excretory ducts. These ducts pass through the medulla of the kidney to the tops of the pyramids and open into the cavity of the renal pelvis (Figure 10). Efferent arteriole

Afferent arteriole

Glomerulus

Glomerular capsule

Distal convoluted tubule Proximal convoluted tubule From renal artery To renal vein Peritubular capillaries

Loop of Henle

Ascending limb Collecting duct

Descending limb

Calyx

Figure 10. A nephron and its blood supply

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The kidneys, due to their function, have double circulation. The small artery that fits the capsule is called the receiving vessel. It breaks up in a capsule into 50 capillary loops forming a glomerulus. The capillaries of the glomerulus are collected in an outflow vessel, through which blood flows from the glomerulus. The transporting vessel, leaving the glomerulus of the capillaries, branches again into the capillaries, which densely twist the convoluted tubules of the first and second order, and then gather into small veins. The latter, enlarged, form a renal vein, which flows into the inferior vena cava. By the time a baby is born, functional immaturity of the kidneys is manifested in many ways. Glomerular filtration in a newborn is 2.5 times weaker than in an adult. In addition, it reaches its level only by the end of the 1st year of life. In the newborn, the kidneys are slightly lower than in older children. Up to 2-3 years, the surface of the kidney is uneven and has a lobed structure. The kidneys in the newborn are closer to each other than in the adult. With age, this distance increases. The mass of a newborn's kidney is 11-12 g. By the year, it triples, and by the age of 15, it increases 10 times. In a newborn, the size of the cortical layer is 1/5, and in an adult, 1/2 of the medulla layer. Consequently, with age, the size of the cortical layer grows most rapidly, its formation ends by 5 years. The growth of the medulla is uneven: mainly is occurs up to three years, at 5-6 years and at 9-12 years. Peculiarities of kidney activity in adulthood and in old age are less studied. The period of aging is characterized by gradual regression of the main renal functions. These phenomena are associated mainly with the changes in the circulatory system of the kidney. In individual nephrons atrophy is observed, their activity is not fully compensated by the remaining ones. The level of glomerular filtration between 50-60 years begins to gradually decline. Urine is excreted from the kidneys through the ureters (tubes up to 30 cm long and 3-6 mm wide) opening into the bladder. The wall of the ureters and bladder consists of three membranes: mucous, muscular and connective tissue. Urine from the kidneys moves due to contractions of the muscular layer and periodically (2-3 times per minute) it enters the bladder. It is a hollow muscular organ with a capacity of up to 750 ml. It is located in the pelvic area. Behind the bladder in men, there is the rectum, in women – the uterus. With a 86

strong filling of the bladder, its tip is adjacent to the anterior abdominal wall. When the volume of urine reaches a certain critical level, the tension of its muscular walls increases, the pressure rises and a reflex urination action occurs. Urine is excreted through the urethra. It has internal and external sphincters. Internal (involuntary) sphincter covers it at the place of the exit from the bladder and opens independently of the will of the person. The outer contracts arbitrarily. The bladder in young children is higher than that of an adult: in the abdominal area, and then it descends into the pelvic area; its capacity in a newborn is 50 ml, at 2 years – 200 ml, at 10 years – 900 ml. Urine formation. It goes in three phases: filtration, reabsorption and secretion. Filtration occurs in the renal glomeruli in the event the blood pressure in the glomerular capillaries exceeds the sum of the oncotic pressure of the blood plasma proteins and the fluid pressure in the glomerular capsule. Filtration is caused by the difference between the hydrostatic pressure of blood in the capillary glomerulus (70 mm Hg), the oncotic pressure of plasma proteins (30 mm Hg) and the hydrostatic pressure of the filtrate of the blood plasma in the glomerular capsule (20 mm Hg). The filtration pressure that determines the glomerular filtration rate is 20 mmHg. In the cavity of the capsule from the blood plasma flowing through the capillaries of the glomerulus, water and all substances soluble in the blood plasma (inorganic substances, urea, uric acid, glucose, amino acids), except proteins, are filtered. The fluid that filters into the lumen of the capsule is similar in composition to the blood plasma and is called the primary urine. Under normal conditions, only traces of plasma proteins are observed in the primary urine, but partially molecular proteins do penetrate the primary urine of a healthy person. The second stage of urination is reabsorption. 1.80 l of urine is produced in human kidneys per day, and 1-1.65 l is excreted. The remaining fluid is sucked back into the tubules. In the proximal nephron, amino acids, glucose, vitamins, proteins, microelements, sodium, chlorine, bicarbonates are completely reabsorbed. In the subsequent sections, only water and ions are absorbed. All biologically important substances for the body have a threshold for elimination. Thus, the release of sugar with urine occurs when its concentration in the blood plasma is 160-180 mg. No threshold substances are completely released at any concentration in the blood plasma. 87

The next step in the formation of urine is tubular secretion. Secretion occurs from the blood into the lumen of the tubule against the concentration and electrochemical gradient. Secretion allows quick release of organic bases and ions. The scheme of the secretory process in the transport of organic compounds is that in the cell membrane of the proximal tubule there is a carrier with affinity to the substance. A complex of the carrier and substance forms, which moves in the membrane and on its inner side disintegrates, releasing the substance and reacquiring the ability to move to the outer side of the membrane and connect with a new molecule of substance. Under normal water conditions, 1-1.5 liters of urine with a density of 1.001% and up to 1.033% is excreted per day. The amount of urine may decrease in the conditions of high temperature, with profuse sweating and at night during sleep. Usually, 25-35 g of urea per day is released in urine, as well as up to 1.2 g of nitrogen in the composition of ammonia, 0.7 g of uric acid, 1.5 g of creatinine formed in muscles, and small amounts of products of protein decay formed in the intestine – indole, skatole, and phenol. Under pathological conditions, acetone, bile acids, protein, glucose and many other substances are detected in the urine. When the concentration of glucose in the blood exceeds 10 mol / l (160-180 mg/%), glycosuria is observed – the excretion of glucose in the urine. The color of urine depends on the volume of diuresis and the excretion of pigments; it changes from light yellow to orange. Pigments are formed from bilirubin in the intestine, where bilirubin turns into urobilin and urochrome. Part of the pigments are oxidized products of hemoglobin decomposition. With age, the amount and composition of urine changes. In children, it is excreted more than in an adult, and urination occurs more often due to the greater amount of water and carbohydrates in the child's diet. In a month-old baby, 350 ml of the urine are excreted, 750 ml – by 1 year, 1.5 L – by 10 years and up to 2 L – by puberty. Then this amount decreases. In a newborn, the urine reaction is sharply acidic, and with age, it becomes slightly acidic. In addition, the newborn has an increased permeability of the renal epithelium, therefore, protein is always found in the urine.

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Regulation of urination. It is carried out by nervous and humoral mechanisms. The kidneys are richly supplied with fibers of the sympathetic and parasympathetic nervous systems. When the sympathetic nerves are irritated, the blood vessels of the kidneys narrow, the amount of blood flowing decreases, and the pressure in the glomeruli drops. This reduces the rate of formation of primary urine, the reverse absorption of water, inorganic substances from the secondary urine. Parasympathetic nerves, on the contrary, dilate blood vessels. In addition, the kidneys receive impulses from the higher nerve centers located in the intermediate medulla. The amount of urine that forms and separates depends on the body's need for water. Absorption of water from the primary urine is enhanced by vasopressin, the antidiuretic hormone of the pituitary gland (ADH), and adrenaline hormone from the adrenal glands causes a decrease in urine formation, as it narrows the renal vessels. The adrenal hormone aldosterone regulates the reabsorption of sodium and potassium salts in the tubules. With an excessive amount of water in the body, the concentration of substances in the blood also decreases and its osmotic pressure drops. This reduces the activity of central osmoreceptors located in the hypothalamus, as well as peripheral ones in the liver, spleen and other organs, which reduces the release of ADH from the neurohypophysis into the blood and leads to increased water excretion by the kidney. With dehydration of the body, the concentration of osmotically active substances in the blood plasma increases, osmoreceptors located in blood vessels are excited, the secretion of ADH increases, water reabsorption increases, urine output decreases and concentrated urine secreted. During stimulation of the mechanoreceptors of the urinary bladder, impulses along the centripetal nerves enter the sacral region of the spinal cord, in which there is a reflex urination center. The first urge occurs when the volume of fluid reaches 150 ml, and reflex urination occurs with a volume of 200-300 ml. The spinal urination center is controlled by the overlying parts of the brain. Inhibition effects come from the cerebral cortex and midbrain, and stimulating effects – from the hypothalamus and pons. To ensure the normal function of the kidneys one should avoid alcohol, spicy food, be cautious when working with toxic substances. 89

The kidneys stabilize the pH concentration in the blood plasma at the level of 7.36. You should be aware that with excessive consumption of meat, more acids are formed, so the urine becomes acidic, and with the consumption of plant food, the pH of the urine shifts to the alkaline side. The urinary reflex is formed by the end of the 1st year of life. Urinary incontinence (enuresis) occurs in 5-10% of children under 15 years of age, more often in boys (70%). The causes of enuresis can be an excessive increase in the excitability of the parasympathetic innervation of the bladder, violation of the regime of work and education, mental trauma, poor living conditions. Children do not tolerate this disease, are nervous, do not fall asleep for a long time, and then plunge into a deep sleep, during which the urge to urinate is not perceived. Prevention of enuresis consists in proper upbringing from an early age, creating normal living conditions, physical development, and strict observance of food and sleep hygiene. Male and female genitals. The testes (testicles), spermoduct (vas deferens), accessory sex glands (prostate gland, seminal vesicles) and the penis represent the male reproductive system. The testicles are located in the scrotum, a special skin-muscular sac located outside the pelvic cavity. The testicle is covered with a dense aluminous membrane, has an oval shape. The average size of the testicle is 4 × 3 × 2 cm. In the testicle, there are lateral and medial surfaces, anterior and posterior margins, upper and lower ends. Spermatozoa are formed in the testes and sex hormones are produced. Mature sperm is pushed out due to muscle contractions from the testicle into the vas deferens. Then they mix with the secretion of the prostate gland and seminal vesicles and form seminal fluid – sperm. Seminal fluid moves through the urethra. This channel passes inside the penis. The male urethra is a tube about 18 cm long, extending from the bladder to the external opening of the urethra. The urethra passes through various formations, so we distinguish three parts: the prostate, webbed and spongy part. The deferent duct is a continuation of the testicular duct. It stretches to the prostate gland, where, when combined with the duct of the seminal vesicle, it passes into the spermatic cord. In the vas deferens, there are four parts: the testicle, the cord, the groin and the pelvic. The outer diameter of the vas deferens is 2-3 mm; the inner diameter is 0.3 mm and it has a star-shaped cross in the section. 90

The prostate gland is located in the pelvic abdominal cavity between the urogenital diaphragm and the bladder neck. The prostate gland surrounds the initial part of the urethra, and its base grows to the bladder. Its shape is compared to a chestnut or truncated cone. In the prostate gland, the base, tip, anterior, posterior and lower lateral surfaces are distinguished. The prostate part of the urethra, in which 3035 prostatic ducts open, opens in a slanting direction into the thickness of the gland. The size of the prostate gland is very variable. Most often, the transverse size of the prostate gland is 4 cm, longitudinal – 3 cm, and anteroposterior – 2 cm. Seminal vesicles are paired glands 6-7 cm long, which are hollow tubes with coiled protrusions. They are located in the pelvis and adjacent to the posterior surface of the bottom of the bladder, located outside the ampoule of the vas deferens. The longitudinal axis of the vesicles is directed from top to bottom and from outside to inside. Seminal vesicles are divided into two sections: the body of the seminal vesicle and the narrowed part of the cervix. The seminal vesicles lie between the two formations, from the inside they are bounded by the vas deferens, from the outside – by the ureter. The penis consists of two cavernous bodies and a spongy body. The cavernous and spongy bodies of the penis are covered with a dense membrane, from which the processes of the trabecular extend into the depths of the bodies of the penis, between which the cells are located. The cavernous bodies of the penis begin with the legs from the inner surface of the lower branches of the pubic bones. At the level of the pubic fusion, the legs of the penis are connected to form a septum of the penis. The spongy body of the penis lies in the groove between the cavernous bodies and forms the urethral surface of the penis. The spongy body permeated throughout the urethra. The skin of the penis is elastic, mobile, contains many sebaceous glands. Behind the neck of the glans penis, there is the foreskin – a fold of skin, usually freely advancing on the head and closing it. The inner surface of the foreskin contains glands of the foreskin that emit a special secret – a prenuptial lubricant. The female reproductive system consists of two sections: internal genitals located in the pelvis are the ovaries, fallopian tubes, uterus and vagina, and the external – large and small labia, clitoris, and the hymen. 91

The ovary is a paired organ, it is the female gonad. The ovary has a medial and lateral surface, free and mesenteric margins, tubal and uterine ends. At the mesenteric region of the ovary, there are gates through which blood vessels enter. The ovarian ligament is composed of muscular and fibrous tissue; it extends from the uterine extremity of the ovary to the lateral aspect of the uterus. The ovary is located in the ovarian fossa, bounded in front by the wide ligament of the uterus, behind it there is a fold of peritoneum. The peritoneal cover is almost completely devoid of the ovary, with the exception of a small area between the free and mesenteric edge, to which a ring – shaped peritoneum is attached (the Fare Valdese ring), strengthening the ovary in the posterior leaflet of the broad ligament of the uterus. The uterus is an unpaired hollow muscular organ located in the pelvic cavity between the bladder in front and the rectum in the back. The egg that enters the uterine cavity through the fallopian tubes in the case of fertilization undergoes further development until the moment the mature fetus is removed during childbirth. In addition to the generative function, the uterus also performs the menstrual one. In the uterus, we distinguish the bottom, body, neck and neck. The uterine cavity is a triangular slit, the base facing the bottom, where the uterine openings of the tubes open in the horns, and from the isthmus to the uterus, the cervical canal extends connecting the uterine cavity with the lumen of the vagina The vagina is a muscle tube 8-10 cm long, which goes from the uterus to the outside and serves to receive the semen and as a birth canal. The entrance to the vagina is located between the skin folds is the lips of the genitals (large and small). At the anterior junction of the labia there is the clitoris – a sensitive organ the size of a pea. The entrance to the vagina in girls is closed with a connective tissue film – the hymen. Near the entrance to the vagina there is the opening of the urethra. Age features. In a newborn girl, in infancy and in early childhood (up to three years), the uterus is cylindrical and flattened in the anteroposterior direction. In the period of the second childhood (8-12 years) the uterus becomes rounded, its bottom expands. In adolescence, it becomes pear-shaped, and this form is preserved in adult women. The length of the uterus in a newborn reaches 3.5 cm, by 10 years it increases to 5-5.5 cm. In an adult woman, the length of the 92

uterus is 6-8 cm. In the period of the second childhood, the length of the body of the uterus and cervix is almost the same. In adolescence, the length of the uterus increases and reaches 5 cm. The mass of the uterus rises slowly at first, and then quickly. In a newborn, it is 3-6 g, in adolescence (12-15 years old) it is approximately 16.5 g, and at 16-20 years, it is 20-25 g. The maximum mass (45-80 g) the uterus has in women aged 30-40 years, and after 50 years, its mass gradually decreases. In the newborn cervical canal is wide; usually it contains a mucus plug. The uterine glands are few, but as the girl grows older, their number increases, the structure becomes more complex, and by the time of puberty, they become branched. The muscular layer of the uterus, poorly developed in newborns, thickens during the growth of the uterus, especially after 5-6 years. In newborn girls, the uterus is tilted anteriorly. The cervix is tilted down and back. The uterus is located high, extruding over the pubic symphysis. Ligaments of the uterus are weak, and therefore it easily shifted to the sides. With the increase in the size of the pelvis and in connection with the lowering of the organs located in it, the uterus gradually moves downwards and occupies a position characteristic of this organ in a mature woman during adolescence. In the old age. due to a decrease in adipose tissue in the small pelvis, uterine mobility increases. The fallopian tubes in the newborn are bent and not in contact with the ovaries. During puberty, due to the growth of the uterus, its wide ligaments and an increase in the pelvic cavity, the fallopian tubes lose their crispiness and descend, approaching the ovaries. The length of the fallopian tube in a newborn is 3.5 cm, and it quickly increases during puberty. Questions for self-control 1. What are the functions of the kidneys? What is the function of the ureters and the bladder? 2. Name the main sections of the urinary system. 3. Describe the structure of the human kidney. 4. Describe the elements of the nephron and indicate what processes occur in each department. 5. Tell us about the mechanism of urine formation. What is primary and secondary urine and what is their difference? 6. What are the age features of the urinary system? What are the features of the structure and functioning of the kidneys in children? 7. How does urination occur and how is urination regulated? 8. How is the nervous and humoral regulation of diuresis provided?

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CHAPTER

8

PHYSIOLOGY OF THE ENDOCRINE GLANDS AND AGE FEATURES At all stages of ontogenesis, the basis of life is metabolism and energy. The normal course of metabolic processes and the functioning of living cells is possible only if there is a constancy of the chemical composition and physicochemical properties of the habitat of the cells in blood, lymph, and tissue fluid. K. Bernard named the combination of these body fluids the "internal environment". The ability of the body to maintain the relative constancy of the chemical composition and physicochemical properties of the internal environment, as well as the most important functions of the body, is called "homeostasis" (from the Greek Homoios – the same, stasis – the state). Walter Cannon coined this term. The basis of homeostasis is self-regulation of functions. This means that any shift in the properties and composition of the internal environment activates the physiological mechanisms that normalize metabolism and energy, growth and development, the implementation of the genetic program, and the interaction of individual parts of the body could not be carried out if the neuroendocrine regulation of the processes did not function. Life activity. In the early stages of prenatal ontogenesis, the chemicals that form in developing cells perform the function of regulation. They are necessary both for stimulation of cell reproduction and for making cell contacts. This kind of chemical bond is maintained throughout life, it plays a significant role in regulation at the local tissue level. However, the effect of these regulators is spatially limited and cannot ensure the coordinated activities of various bodies. At its core, 94

it is an evolutionarily more ancient method of biological control. In the later stages of fetal development, specialized organs called endocrine glands appear. The endocrine glands (Figure 11) are the glands that have no excretory ducts and release their products – hormones – directly into the blood, lymph or cerebrospinal fluid. These glands are intercomnected, affecting each other's activities on the basis of feedback. Hormones are organic substances of various chemical nature – amino acids, proteins, steroids. Female

Male

Pineal gland

Pituitary gland

Thyroid gland Thymus

Adrenal gland

Pancreas

Ovary Testis

Figure 11. The major endocrine glands of the human body.

The endocrine glands provide humoral regulation of the metabolism (protein, carbohydrate, fat and mineral), growth, development, cardiovascular activity and other systems of the human body. Similarly, they regulate the activity of the body and unite it into a single whole nervous system. They act in concert, in one direction, but there are significant differences. Humoral regulation exerts its effect more slowly (within a few minutes or hours), while nervous regulation 95

occurs in a split second. The influence of the products of the endocrine system is longer than that of the products of the nervous one. The nervous system regulates the work of all the endocrine glands, and hormones in turn affect the functions of the nervous system. Otherwise, the endocrine glands are subject to control by the nervous system, therefore a single neurohormonal regulation of functions develops. It exercises central control, coordination and integration of the functioning of numerous cells, tissues and organs of the human body. The endocrine glands include the pituitary gland, the thyroid gland, the parathyroid gland, the adrenal glands, the pancreas, the sex glands (testes and ovaries), and the thymus gland (thymus gland). The pancreas and the sex glands are mixed glands, which are both glands of internal and external secretion. More than 100 years ago, it was discovered that not all parts of the pancreas are associated with the excretory ducts. Subsequently, it turned out that this gland has a double secretion. Some of its areas produce juice that enters through the excretory ducts into the duodenum, while other areas, called islets, function as endocrine glands. They have no excretory ducts and are very abundantly supplied with blood vessels, to which the hormone produced in these areas – insulin – gets, contributing to the conversion of glucose into animal starch. In addition to the main endocrine glands, some areas of the brain, especially the hypothalamus, as well as the mucous membrane of the stomach and small intestines, the placenta, and possibly some other organs, have an intra-secretory function. A temporary, but very important function is performed in the female body by the placenta. Finally, there are separate cell groups along the gastrointestinal tract, in the liver and kidneys, which secrete hormones or hormone-like substances. Many hormones of peptide structure are found in the brain, where they modulate the transmission of nerve impulses through synapses. Currently, more than 40 hormones are known. Many of them are well studied, and some are even artificially synthesized and widely used in medicine for the treatment of various diseases. Hormones are most often classified by chemical structure or by the glands that produce them (pituitary, corticosteroid, sex, etc.). Another approach to the classification of hormones is based on their functions (hormones that regulate water and electrolyte metabolism, 96

glycaemia, etc.). According to this principle, hormonal systems (or subsystems) are singled out, including compounds of different chemical nature. Endocrine diseases can be determined by the deficiency or excess of a specific hormone. Hyperactive secretion of hormones depends on genetic (congenital absence of the enzymes involved in the synthesis of this hormone), dietary (hypothyroidism due to iodine deficiency in the diet), toxic (necrosis of the adrenal cortex under the influence of insecticide derivatives), immunological (appearance of antibodies that destroy the adrenal gland or other glands) factors. The characteristic properties of hormones are physiological activity, that can cause significant changes in the body (in the growth, differentiation, development, change in metabolism), and a specific effect on a strictly defined type of metabolic processes or a certain tissue, rapid destruction in tissues, in particular, in the liver (therefore, a constant release of hormones by the corresponding gland is required). Distinctive properties of hormones are high biological activity, that is, the ability to have an effect in extremely low concentrations (micrograms, nanograms); specificity of action, by virtue of which the deficiency of one hormone can be replaced by another one or a biologically active substance; distant action, i.e. the ability of the hormone to influence the organs and tissues located far from the place of its production. The chemical nature of hormones and biologically active substances of humans and animals is different. The duration of its biological action depends on the complexity of the structure of the hormone, for example, from fractions of a second in mediators and peptides up to hours and days in steroid hormones and iodothyronines. The analysis of the chemical structure and physicochemical properties of hormones helps to understand the mechanisms of their action, develop methods for their determination in biological fluids, and carry out their synthesis. Classification of hormones and biologically active substances by chemical structure: – Amino acid derivatives: tyrosine derivatives: thyroxin, triodothyronine, dopamine, epinephrine, norepinephrine; tryptophan derivatives: melatonin, serotonin; histidine derivatives: histamine. 97

– Protein-peptide hormones: polypeptides: glucagon, corticotrophin, melanotropin, vasopressin, oxytocin, peptide hormones of the stomach and intestines; simple proteins: insulin, somatotropin, prolactin, parathormone, calcitonin; complex proteins (glycoproteins): thyrotrophic, phollitropin, lutropin. – Steroid hormones: corticosteroids (aldosterone, cortisol, corticosterone); sex hormones: androgens (testosterone), estrogens and progesterone. – Derivatives of fatty acids: arachidonic acid and its derivatives: prostaglandins, prostacyclin, thromboxane, leukotrienes. Hormones exert their effect either directly acting on tissues or organs, stimulating or inhibiting their work, or indirectly, through the nervous system. The mechanism of direct action of certain hormones (steroid, thyroid hormones, etc.) is associated with their ability to penetrate cell membranes and interact with intracellular enzyme systems, changing the course of cellular processes. Large peptide hormones cannot freely penetrate cell membranes and have a regulating effect on cellular processes with the help of special receptors located on the surface of cell membranes. It is interesting to note that every moment many hormones act on the cells, but only cellular processes, the effect of which provides the most appropriate effect, influence those. Special substances – prostaglandins, determine the expediency of the effect of hormones on cellular processes. They perform, figuratively speaking, the function of the controller that inhibits the effect on the cell of those hormones whose action is currently undesirable. The mediated action of hormones through the nervous system is also ultimately associated with their effect on the course of cellular processes, which leads to the changes in the functional state of nerve cells and, accordingly, changes in the activity of the nervous centers that regulate certain functions of the body. In recent years, evidence has been obtained that hormones "interfere" even in the activity of the hereditary apparatus of the cells: they affect the RNA system and cellular proteins. For example, some of the hormones of the adrenal glands and sex glands have such an effect. According to modern data, some neurons are capable of secreting physiologically active substances, in addition to their main functions. In particular, the hypothalamus neurons play an especially important role in neurosecretion, which 98

anatomically is closely connected with the pituitary gland. It is the neurosecretion of the hypothalamus that determines the secretory activity of the pituitary gland, and through it all other endocrine glands. Depending on the external influences and the state of the internal environment, the hypothalamus, first, coordinates all the vegetative processes of our body, performs the functions of the highest vegetative nerve center; secondly, it regulates the activity of the endocrine glands, transforming nerve impulses into humoral signals, which then enter the corresponding tissues and organs and change their functional activity. Despite such a perfect regulation of the activity of the endocrine glands, their functions significantly change under the influence of pathological processes. Perhaps, an increased secretion of endocrine glands is a hyperactive function of the glands, or a decrease in secretion is a hypofunction. Disruption of the endocrine system, in turn, affects the vital processes of the body. In general, the endocrine glands regulate all major metabolic processes, maintaining them at the required level, which can vary significantly depending on the state of the body and environmental conditions. The intensity of the formation of various hormones varies accordingly, and a kind of self – regulation of the gland often occurs: it reduces the secretion of the hormone as soon as the changes caused by it become excessive. Thus, for example, by reducing the blood glucose level, the pancreas begins to release less insulin, and the glucose level returns to normal. In many cases, the necessary level of a particular metabolic process is supported by the interaction between the glands. Thus, one of the hormones of the anterior lobe of the pituitary gland stimulates the function of the thyroid gland. However, its formation is inhibited by the thyroid hormone, which at the same time stimulates the production of growth hormone. Special hormones of the anterior pituitary gland stimulate the function of the adrenal glands and some other endocrine glands. Especially important for the regulation of the endocrine glands is the nervous system. First, the impulses coming along the nerves can affect the intensity of secretion. Secondly, the hypothalamus of the diencephalon as the highest nerve center of regulation of metabolism and the activity of internal organs directly connected with the pituitary gland, forms the so-called 99

hypothalamic is pituitary system. In some nuclei of the hypothalamus, there are special neurons that can not only conduct excitation, but also release into the blood active substances that stimulate the formation of hormones of the anterior pituitary gland. In the neurons of other nuclei of the hypothalamus hormones are formed, which, along axons, descend into the posterior lobe of the pituitary gland, and from there enter the blood. Pituitary is divided into three lobes or parts: anterior (adenohypophysis), middle and posterior (neurohypophysis). The following hormones are produced in the anterior lobe of the pituitary: somatotropin (or growth hormone is growth hormone), adrenocorticotropic hormone (ACTH), thyrotropin (or thyroid stimulating hormone, which stimulates the function of the thyroid gland), gonadotropic hormones (androgen – male sex hormone, and estrogen – female sex hormone), lactogenic hormone or prolactin, which stimulates milk production during pregnancy. In the middle lobe of the pituitary gland, a melanocyte – stimulating hormone (intermeddling) is produced. It stimulates the discoloration of the skin during pregnancy and adrenal insufficiency. Neurohypophysis produces hormones vasopressin (antidiuretic) and oxytocin. The first causes vasoconstriction and reduces the excretion of urine; the second – the contraction of the muscles of the uterus. The pituitary gland is regarded as the central endocrine gland because it controls the activity of other endocrine glands. Tropic hormones regulate the secretion of hormones of the pituitary – dependent glands according to the feedback principle: when the concentration of a certain hormone in the blood decreases, the corresponding cells of the anterior pituitary gland secrete the tropic hormone that stimulates the formation of the hormone by this particular gland. Conversely, an increase in the hormone content in the blood is a signal to the pituitary cells, which respond by a slower secretion. The pituitary mass in a newborn child is 0.12 g; it doubles by the age of 10, triples by 15, reaches its maximum by 20, and after 60 years slightly decreases. The epiphysis cerebri or pineal gland is located in the epithalamus, near the center of the brain, in a groove where the two halves

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of the thalamus join. It is rounded; its mass in an adult does not exceed 0.2 g. The epiphysis contains glandular cells called pinealocytes. The function of pinealocytes has a clear daily rhythm: at night, melatonin is synthesized, in the afternoon – serotonin. This rhythm is associated with light, as light inhibits melatonin synthesis. In a newborn child, the mass of the epiphysis is about 7 mg, during the first year it reaches 100 mg and doubles by 10 years, after which it practically does not change. In old age, cysts can appear in the epiphysis, "brain sand" can be deposited, so its mass increases. The thyroid gland secretes the hormones thyroxin and triodothyronine, which enhance oxidative processes, affect water, protein, carbohydrate, fat, mineral metabolism (chlorides), growth, development and differentiation of tissues. The thyroid gland begins to develop on the 4th week of embryonic development. In a newborn child, the mass of the gland is 5-6 g, by the year it decreases to 2-2.5 g, then gradually increases, and in old age, the mass decreases. In the areas where the soil and water are poor in iodine, there are numerous cases of insufficiency of the thyroid gland with a significant growth of its tissue (goiter). This is accompanied by exophthalmus, an increase in basal metabolism and body temperature, an increase in food intake, and with weight loss. A lack of thyroxin in childhood leads to growth retardation, retardation of puberty, mental development (cretinism). In adults, a lack of thyroxin leads to a decrease in basal metabolism, edema, and a decrease in body temperature, a slowdown in speech, thinking, and general apathy (myxedema). During puberty, an increase in gland size sometimes is observed. Parathyroid glands produce parathyroid hormone that regulates the level of calcium and phosphorus in the blood, affecting the excitability of the nervous and muscular systems. The hormone acts on the bone tissue, causing an increase in osteoclast function. Hypofunction of the glands leads to cramps in the respiratory movements. In newborns, the mass of the parathyroid glands does not exceed 10 mg, by the year, it reaches 20-30 mg, by the age of five it doubles, and by the age of 20, it reaches a constant value, without changing throughout the whole life of a human. Adrenal glands are paired glands adjacent to the upper ends of the kidneys, they consist of medulla and cortex. The medulla secretes 101

the hormones adrenaline and norepinephrine, which affect the heart, small arteries, blood pressure, basal metabolism, the muscles of the bronchi and the gastric tract. The adrenal cortex releases three groups of hormones: mineralocorticoids (aldosterone, corticosterone), which regulate mineral metabolism and glucocorticoids (hydrocortisone, cortisone) that regulate protein, fat and carbohydrate metabolism, sex hormones (androgens, estrogens) that regulate the activity of the genitals. Distortion of corticosteroid secretion leads to the change in the work of the heart, emaciation, fatigue, discoloration of the skin (the so-called "bronze disease"). Pancreas is a mixed gland. Its intra secretory function is performed by clusters of special cells (islets of Langerhans) producing the hormones insulin and glucagon, which enter the blood and affect carbohydrate metabolism. The increase in the level of insulin leads to the increase in glucose consumption by tissue cells, the deposition of glycogen in the liver and muscles, and a decrease in the concentration of glucose in the blood. It is necessary for the breakdown of glycogen to glucose. The damage of the intra secretory part of the pancreas causes an increase of sugar levels in the blood; it begins to be excreted in the urine (sugar disease, or diabetes, see Lecture No. 6). Paraganglia. The paraganglia include chromaffin and nonchromaffin paraganglia, made of glomus cells, they are located at the beginning of the external and internal carotid arteries, the lumbar aortic paraganglia are at the anterior surface of the abdominal aorta. They produce adrenaline and norepinephrine. Lumbar aortic paraganglia are present in newborns and infants, after 1 year they begin to reverse their development, by 2-3 years they disappear. These are small thin strips located on both sides of the aorta. Paraganglia consist of typical chromaffin cells, their connective tissue degeneration occurs with age. The chromaffin ganglia are small, have the shape of a rice grain, and are located on the back or medial surface of the common carotid artery at the place of its division into the external and internal ones. The cardiac paraganglion is unstable, located between the pulmonary trunk and the aorta. Paraganglia are also found in the subclavian and renal arteries. The endocrine part of the genital glands. The sex glands (testicle and ovary) produce sex hormones that are released into the blood. 102

Interstitial endocrinocytes carry out this function in the testicle. These large cells are located in clusters between the seminiferous tubules near the blood capillaries. Male hormones androgens (testosterone) affect the development of the genital organs, secondary sexual characteristics, and the musculoskeletal system. In the testicles, a small amount of estrogen is synthesized. Female sex hormones are produced in the ovary. Cells of the follicular epithelium produce estrogens. Cells of the corpus luteum – luteocytes – produce progesterone. In addition, a small number of androgens is formed in the ovaries. Estrogens provide the development of the body as the female body. Progesterone affects the uterine lining, preparing it for implantation of a fertilized egg. The effect of hormones on the growth of the body. Growth processes in the body are determined by the action of a number of hormonal factors. The main of them is somatotropin – a hormone of the anterior pituitary gland. Under its effect, a neoplasm of cartilage tissue of the epiphyseal zone and an increase in the length of the tubular bones occur. At the same time, under the action of somatotropin, the formation of soft connective tissue is activated, which is important for ensuring the reliability of the connection of parts of the growing skeleton. It has a stimulating effect on the development of skeletal muscle tissue. The effect of growth hormone sharply decreases with insufficient content in the blood of thyroid hormones and insulin. Thyroid hormones are required to normalize the processes of cell reproduction and differentiation. The classical signs characterizing impaired growth and development of children and adolescents with hypothyroidism are lagging body length, delayed skeletal ossification and dental development. These manifestations are combined with slowed heart rate, lowered blood pressure, reduced tone and strength of skeletal muscles. No less significant is the role of insulin. Thus, it increases the transport of amino acids through the membrane and is involved in the provision of protein synthesis of building materials. In addition, insulin promotes carbohydrate nutrition of cells. Testosterone has a mediatory effect on the growth. It stimulates protein synthesis in cartilage and bone tissue, skeletal muscle, myocardium, liver, kidneys. This is most pronounced during puberty. The 103

stimulating effect on growth continues until the closure of the epiphyseal growth zones. Estrogens exert an inhibiting effect on the overall growth of the body, activating the ossification of the epiphyseal zones of growth of the tubular bones. Estrogens stimulate the growth and protein synthesis in the female genital organs and, to a lesser extent, in the kidneys, liver, myocardium. Parathyroid hormone, calcitonin and the hormonal form of vitamin D3 also provide the normal course of growth processes. This group of hormones is of a paramount importance in the formation of bone tissue and in maintaining calcium homeostasis in the internal environment of the body and in the cells. Calcitonin and parathyroid hormone affect calcium metabolism in close interaction with the hormonal form of vitamin D3, which is formed from cholecalciferol, which comes from food. Glucocorticoids have an opposite effect on the growth of the organism. Thus, in the treatment of children and adolescents with massive doses of glucocorticoids, growth is delayed. This may explain growth retardation when the stress factors act on the body, regardless of their nature. Therefore, during stress, the whole system of corticoliberin – corticotropin – glucocorticoids is activated. Given this fact, it is necessary to eliminate the prolonged effect on the children's body of stress factors, including physical activity of a large load and intensity, as well as frequent participation in competitions. The effect of hormones on the development of the nervous system and behavior. Of the hormonal factors that influence the development of the central nervous system, the thyroid hormones are the most significant. The lack of hormones in the last trimester of pregnancy and the first weeks after birth is the cause of the development of such a disease as cretinism. The role of thyroid hormones is high in the first 18 months after birth. The deficiency of thyroxin and triiodothyronine sharply inhibits the differentiation of nerve cells. If the lack of these hormones occurs after 18 months, then the growth is mainly disturbed, and mental developmental defects are less pronounced. Early administration of thyroid hormones helps to restore mental development. It has been found that a deficiency of thyroid hormones during critical 104

periods of brain development leads to a decrease in protein synthesis in brain tissue and a decrease in the content of protein synthetic enzymes in it. The development of the vascular system of the brain is also impaired, and the morphological differentiation of the cerebral cortex and cerebellum is delayed. Consequently, thyroid hormones are necessary for the structural, biochemical and functional maturation of brain tissue. Adrenal hormones have a significant effect on the nervous system, changing the strength of the nervous processes. Removal of the adrenal cortex is accompanied by the dysfunction of the entire HNA. Sex hormones affect the ratio of excitation and inhibition. The performance of the nervous system is largely affected by male sex hormones. Resoluteness, aggressiveness are also determined by the concentration of male sex hormones. Removal of the sex glands or their pathological underdevelopment in childhood causes mental disturbance and often leads to mental disability. Optimal physical activity increases the reserve capacity of the endocrine system and, thereby, indirectly affects the overall state of the nervous system and the whole body. The role of hormones in the adaptation of the organism to physical exertion. In adapting, the body to physical stress hormones play a crucial role. In the assembly of the endocrine glands, the sympathoadrenal and pituitary-adrenal systems are the first to react to the muscular load. In the process of performing muscular work, along with a high level of functioning of the sympathoadrenal and pituitary – adrenal systems, the content of aldosterone, vasopressin and thyroxin increases. Later, additional production of insulin, somatotropin, and glucagon is included. Such a variety of hormonal substances is necessary for the mobilization of energy resources, ensuring gas exchange and nutrition of the tissues of the working organism. Long-term performance of muscular work leads to a decrease in the activity of hormonal mechanisms that ensure the mobilization of energy and plastic resources. In parallel, there is an increase in the blood calcitonin. This reaction is protecting the body from the critical use of energy and plastic reserves. During the recovery period, the concentration of hormonal substances normalizes. In younger children (up to 7-8 years old), prestart and starting reactions are either absent or weakly expressed. They are developed only in the process of systematic training and are most pronounced 105

at the age of 13-15 years, when the starting reactions often exceed those of adult athletes. Systematic exercise leads to an increase in the activity of the adrenal cortex. Therefore, the excretion of steroid hormones is higher in children involved in sports. However, excessive in duration and intensity of muscle loads and performed on the background of incomplete recovery physical exercises dramatically reduce the functional activity of the adrenal cortex. Activation of the adrenal cortex in response to muscle load decreases as it matures. In children, these changes are less adequate and more pronounced. The effect of training loads on the functions of the thyroid gland, thymus, and pineal gland in children is not fully understood. It has been established that the muscular load activating the adrenal glands inhibits the function of the thyroid gland. The function of the sex glands is stimulated by adequate physical activity in children and adolescents. Large exhaustive loads lead to inhibition of the production of sex hormones, delaying puberty, especially if increased physical activity occurs before the onset of puberty. Therefore, when assessing adaptive rearrangements occurring in the life support systems of adolescents (especially girls), it is necessary to take into account the intensity of androgenic function. Disorders of hormonal function associated with physical overload, manifested in an increased elimination of androgens with urine, should serve as a signal to reduce the load or change its qualitative composition. Questions for self-control 1. What glands are classified as endocrine? 2. What are hormones? 3. What are the features of the structure and functions of the pituitary gland? 4. Where is the pineal gland located and what hormones does it produce? 5. What are the features of the secretory activity of the thyroid gland? What processes regulate thyroid hormones? 6. What are the functions of adrenal hormones? 7. What is the endocrine function of the pancreas? 8. What are the age-related features of functioning of the endocrine glands: pituitary, pineal, thyroid, thymus, adrenal glands, and sex glands?

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CHAPTER

9

DEVELOPMENT OF THE NERVOUS SYSTEM. HIGHER NERVOUS ACTIVITY AND ITS FORMATION DURING THE DEVELOPMENT OF A CHILD The nervous system coordinates and regulates the activity of all organs and systems, ensuring functioning of the body as a whole; it serves to the adaptation of the body to the changes in the environment, maintains the constancy of its internal medium. Topographically, the human nervous system is divided into central and peripheral ones. The central nervous system includes the spinal cord and brain. The peripheral nervous system consists of the spinal and cranial nerves, their roots, branches, nerve endings, plexuses and nodes, which lie in all parts of the human body. According to the anatomical and functional classification, the nervous system conventionally is divided into somatic and vegetative. The somatic nervous system provides the innervation of the body – the skin, skeletal muscles. The vegetative nervous system regulates metabolic processes in all organs and tissues, as well as growth and reproduction, innervates all internal organs, glands, smooth muscles of organs, and the heart. The nervous system develops from the ectoderm, through the stages of the neural strip and the brain groove with the subsequent formation of the neural tube. From its caudal part, the spinal cord develops, from the rostral part, first 3 and then five brain vesicles are formed, from which the intermediate, middle, posterior and medulla brain develop. This differentiation of the central nervous system occurs at the third or fourth week of embryonic development. 107

In the future, the brain volume increases more intensively than the spinal one and by the time of birth it averages 400 g. Moreover, in girls, the brain mass is slightly lower than in boys. The number of neurons at the time of birth corresponds to the level of an adult, but the number of branches of axons, dendrites and synaptic contacts increases significantly after birth. The most intensively the mass of the brain increases during the first 2 years after birth. Then the pace of its development slightly reduces, but continues to remain high until 6-7 years. The final maturation of the brain ends by 17-20 years. By this age, its average weight in men is 1400 g, and in women – 1250 g. The development of the brain is heterochronous. First, those nervous structures ripen on which the normal vital activity of the organism at this age stage depends. The functional usefulness is reached, first, by the stem, subcortical and cortical structures, which regulate the vegetative functions of the organism. In terms of their development, these departments approach the state of an adult already at the age of 2-4 years. Spinal cord. During the first three months of intrauterine life, the spinal cord occupies the spinal canal along its full length. In the future, the spine grows faster than the spinal cord. Therefore, the lower end of the spinal cord rises in the spinal canal. In a newborn child, the lower end of the spinal cord is at the level of the III lumbar vertebra, in the adult – at the level of the II lumbar vertebra. The spinal cord of a newborn has the length of 14 cm. By 2 years, the length of the spinal cord reaches 20 cm, and by 10 years, compared to the neonatal period, it doubles. The thoracic segments of the spinal cord grow the fastest. The mass of the spinal cord in a newborn is about 5.5 g, in children of the 1st year – about 10 g. By the age of 3 years, the mass of the spinal cord exceeds 13 g, and by the age of seven, it is about 19 g. In a newborn, the central channel is wider than in an adult. The decrease in its lumen occurs mainly within 1-2 years, as well as in the later age periods, when an increase in the mass of gray and white matter is observed. The volume of the white matter of the spinal cord increases rapidly, especially due to the own beams of the segmental apparatus, the formation of which occurs at an earlier date compared with the periods of the formation of the conducting paths. Medulla. By the time of birth, it is fully developed in both anatomical and functional terms. Its mass reaches 8 g in a newborn. The medulla oblongata occupies a more horizontal position than in adults and is distinguished by the degree of myelination of the nuclei and pathways, 108

the size of the cells and their location. As the fetus develops, the size of the nerve cells of the medulla oblongata increases, while the size of the nucleus with the growth of the cell decreases relatively. Nerve cells of a newborn have long processes; their cytoplasm contains a toroid substance. The nuclei of the medulla are formed early. The development of the regulatory mechanisms of respiratory, cardiovascular, digestive, and other systems in ontogenesis is associated with their development. Cerebellum. In the embryonic period of development, the ancient part of the cerebellum is first formed, and then its hemisphere. At the 4th-5th month of intrauterine development, the superficial parts of the cerebellum grow, and furrows and gyros form. The cerebellum grows most intensively in the first year of life, especially from the 5th to the 11th month, when the child learns to sit and walk. In a one-year-old child, the mass of the cerebellum increases by four times and averages 95 g. After this, a period of a slow growth of the cerebellum begins, by 3 years the size of the cerebellum approaches its size in an adult. A 15-year-old child has a cerebellum mass of 150 g. In addition, a rapid development of the cerebellum also occurs during puberty. The gray and white matter of the cerebellum develops unequally (Figure 12). Cerebrum

Cerebral cortex Thalamus

Corpus callosum

Hypothalamus Pituitary gland

Pons Reticular activating system

Cerebellum Medulla

Figure 12. Brain structure and functions.

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In a child, the growth of gray matter is relatively slower than of white matter. So, from the neonatal period to 7 years, the amount of gray matter increases by about 2 times, and of white matter – by almost 5 times. Of the nuclei of the cerebellum prior to the others, a dentate nucleus is formed. Starting from the period of prenatal development and to the first years of life of a child, nuclear formations are better expressed than nerve fibers. The cellular structure of the cerebellar cortex in a newborn is significantly different from that in an adult. Its cells in all layers differ in shape, size and number of processes. In the newborn, the Purkinje cells are not yet fully formed, the toroid substance is not developed in them, the nucleus almost completely occupies the cell, the nucleolus has an irregular shape, and the dendrites of the cells are weakly developed. The formation of these cells is rapid after birth and ends by 3-5 weeks of life. The cellular layers of the cerebellar cortex in a newborn are much thinner than in an adult. By the end of the 2nd year of life, their sizes reach the lower limit of magnitude in an adult. The complete formation of cellular structures of the cerebellum is observed by 7-8 years. Bridge. In a newborn, it is higher than that of an adult, and by the age of five, it is at the same level as that of a mature person. The development of the bridge is associated with the formation of the legs of the cerebellum and the establishment of connections of the cerebellum with other parts of the central nervous system. The internal structure of the bridge in a child has no distinctive features compared with an adult. The nuclei of the nerves located in it by the birth period are already formed. The middle brain. Its shape and structure is almost the same as in an adult. The nucleus of the oculomotor nerve is well developed. The red nucleus is well developed, its macro cellular part, which provides the transmission of impulses from the cerebellum to the motor neurons of the spinal cord, develops earlier than the small cell, through which the excitation is transmitted from the cerebellum to the subcortical formations of the brain and to the cortex of the big hemispheres. In the newborn, the Substantia nigra (black substance) is a well-defined formation, the cells of which are differentiated. However, a significant part of the cells of the substantia nigra has no characteristic pigment

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(melanin), which appears from 6 months of life and reaches its maximum development by 16 years. The development of pigmentation is in direct relation with the improvement of the functions of the substantia nigra. The intermediate brain. Separate formations of the diencephalon have their own pace of development. The optic thalamus forms by 2 months of intrauterine development. At the 3rd month, the thalamus and hypothalamus a demarcated. At the 4th-5th month, bright layers of developing nerve fibers appear between the nuclei of the thalamus. At this time, the cells are still poorly differentiated. At 6 months, the cells of the reticular formation of the optic thalamus becomes clearly visible. Other nuclei of the optic thalamus begin to form from 6 months of intrauterine life, by 9 months they are well expressed. With age, their further differentiation occurs. The increased growth of the optic thalamus occurs at 4 years of age, and the size of an adult it reaches at 13 years of age. In the embryonic period of development, the subthalamic area is laid in, but in the first months of intrauterine development of the hypothalamus nucleus, it is not differentiated. Only at the 4-5th month, there is an accumulation of cellular elements of the future nuclei, at the 8th month they are well expressed. The nuclei of the hypothalamus ripen at different times, mainly by 2-3 years. By the time of birth, the structure of the ashen tuber is not yet fully differentiated, which leads to imperfect thermoregulation in newborns and children of the first year of life. Differentiation of cellular elements of the ashen tuber ends at the latest by 13 years. Cerebral cortex. The cerebral cortex is phylogenetically the youngest and at the same time complex part of the brain, designed to process sensory information, to form behavioral responses of the body. The cerebral cortex is divided into the ancient part (olfactory bulb, olfactory tract, and olfactory tubercle), the old part (part of the limbic system) and the new cortex. New cortex occupies 95-96% of the total area and 4-5% falls on the share of the ancient and old cortex. The thickness of the cortex varies from 1.3 to 4.5 mm. The area of the cortex increases due to furrows and gyring. In an adult, it is 2200 cm² The cortex consists of gray and white matter, as well as neuroglia. The number of neurons is 16-18 billion. Glial cells perform a trophic function. 111

Functionally, neurons of the cortex are divided into 3 types: afferent (sensory) – nerve fibers of the afferent paths approach them, associative (intercalated) ones are within the brain and spinal cord, efferent (motor) neurons form descending (efferent) pathways from cortex to different nuclei of the brain and spinal cord. The sensory cells include stellate cells that are built in the 3d and 4th layers of sensory areas of the cortex. The efferent neurons include neurons of the 5th layer of the motor zone, which are represented by giant pyramidal Betz cells. Associative cells include spindle-shaped and pyramidal cells of 3 layers. Due to the fact that the bodies and processes of the neurons described above have an ordered arrangement, the core is built according to the screen principle, i.e., the signal focuses not from a point to a point, but on a multitude of neurons, which provides a complete analysis of the stimulus, as well as the possibility of transmitting the signal to other areas of the cortex that are interested in it. The cortex consists of seven layers: – Molecular layer – small neurons and fibers. Here afferent thalamocortical fibers come from nonspecific nuclei of the thalamus, which regulate the level of excitability of cortical neurons. – The outer granular layer is represented by small neurons in the form of grains and small pyramidal cells. – The outer pyramidal layer is made up of pyramidal cells of various sizes. Functionally, the II and III layers of the cortex unite neurons, the processes of which provide corticocortical associative connections. – The inner granular layer is represented by stellate cells (cellgrains). Afferent thalamocortical fibers coming from projection nuclei of the thalamus end here. – The inner pyramidal layer is represented by large pyramidal cells. The most pyramidal cells are Betz cells, their axons go to the brain and spinal cord. – Polymorphic layer (multiform) is multi shaped neurons that have a triangular and spindle-shaped form. – Fusiform neurons are found in some areas of the cortex. These neurons bind all layers of the cortex, their fibers rise to the 1st layer. The functional unit of the cortex is a vertical column consisting of seven cells; they react together to the same stimulus. 112

In the cortex, there are three zones, based on the location of the neurons: – Sensory zones are the input areas of the cortex, which, through the ascending nerve pathways, receive sensory information from most receptors in the body. – Associative zones 1) Associate newly arriving sensory information with previously received and stored in memory blocks, thanks to which new stimuli are "recognized", 2) Information from some receptors is compared with sensory information from other receptors, 3) Participate in the processes of memorization, learning and thinking. – The motor zones are the exit areas of the cortex. In them, motor impulses arise, going to arbitrary muscles along the descending paths that are in the white matter of the big hemisphere. Until the 4th month of fetal development, the surface of the big hemispheres is smooth and only an indentation of the future lateral sulcus is noted on it, which finally forms only by the time of birth. The outer cortical layer grows faster than the inner one, which leads to the formation of folds and furrows. By 5 months of prenatal development, the main furrows are formed: lateral, central, corpus callosum, parietal – occipital, and spur. Secondary grooves appear after 6 months. By the time of birth, the primary and secondary furrows are well defined, and the cortex of the big hemispheres has the same type of structure as in the adult. However, the development of the form and size of the furrows and convolutions, the formation of small new furrows and convolutions continues after birth. By the time of birth, the cerebral cortex has the same number of nerve cells (14-16 billion) as the cerebral cortex of an adult. However, the nerve cells of the newborn are immature in structure, have a simple fusiform shape and a very small number of processes. The gray matter of the cerebral cortex is poorly differentiated from the white. The cerebral cortex is relatively thin, the cortical layers are poorly differrentiated, and the cortical centers are not sufficiently formed. After birth, the cerebral cortex develops rapidly. The ratio of gray and white matter to 4 months is approaching the ratio of an adult. By 9 months, the first three layers of the cortex become more distinct, and by 1 year, 113

the general structure of the brain approaches a mature state. The arrangement of the layers of the cortex, the differentiation of nerve cells is completed by 3 years. At primary school age and during puberty, the continuing development of the brain is characterized by an increase in the number of associative fibers and the formation of new neural connections. During this period, the brain mass increases slightly. In the development of the cerebral cortex, a common principle works – first, phylogenetically older structures are formed, and then – the younger ones. During the 5th month, nuclei regulating motor activity appear earlier than other ones. During the 6th month, the nucleus of the skin and visual analyzer appears. Later than others develop phylogenetically new areas: frontal and inferior (at the 7th month) ones, then the temporal parietal and parietal – occipital areas. Moreover, the phylogenetically younger sections of the cortex of the big hemispheres relatively increase with age, while the older ones, on the contrary, and decrease. Higher nervous activity. This is the activity of the higher parts of the central nervous system that provide the perfect adaptation of animals and humans to the environment. The structural basis of the higher nervous activity in humans is the cerebral cortex, along with the subcortical formations closest to it. The function of these sections is the implementation of complex reflex reactions. Unconditioned reflexes are relatively constant, occurring in response to adequate stimulation, and serve as the basis for the formation of numerous conditioned reflexes. Unconditioned reflexes provide coordinated activities aimed at maintaining the internal environment and the interaction of the body with the external environment. Unconditioned reflexes are innate, hereditarily transmitted reactions of the body. First, they are divided into simple and complex ones. A special group is formed by the most complicated unconditioned reflexes, among which there are individual (food, defensive, research, etc.) and specific (sexual and parental) reflexes. A special place among the unconditioned reflexes belongs to an indicative reflex or a reflex to novelty. It arises in response to any rapidly occurring environmental change and is expressed externally in alarming, listening, turning the eyes and head, and sometimes the entire body in the direction of a new stimulus. The difference of the orienting reflex from other unconditioned reflex reactions is that it 114

weakens relatively quickly or it fades away with repeated application of the same stimulus. Thus, the unconditioned reflex is a reaction of the body to directly acting stimuli, promoting the interaction of the organism with the environment and having an adaptive value for it. Conditioned reflexes. Conditioned reflexes are reactions acquired by the body in the process of individual development based on "life experience". They are adaptive in nature, which makes the behavior more plastic, adapted to specific environmental conditions. Any conditioned reflexes require the participation of higher parts of the brain in their acquisition or loss in the individual, they have a signaling character, i.e. prevent the subsequent occurrence of an unconditioned reflex, preparing the body for it. Conditioned reflexes, differing in the features of from the unconditional ones require for their development the following conditions: – The conditioned stimulus must precede the unconditioned one, – The importance of the unconditioned stimulus must be greater than the conditioned one, – Normal functioning of the brain. Reinforcement. Depending on the presence or absence of reinforcement, conditioned reflexes are divided into positive (reinforced), causing an appropriate reaction of the body, and negative or inhibitory (unsupported), which not only do not cause a corresponding reaction, but also weaken it. If the conditioned reflex is developed on the basis of unconditioned reflex, then it is a first – order reflex. If it is based on a previously developed conditioned reflex, then it called a second – order conditioned reflex. Accordingly, conditioned reflexes of higher orders are possible. In children, reflexes of the sixth order have been described. In adults, conditioned reflexes of the 2-20th order are formed. Differences of unconditioned and conditioned reflexes. Unconditioned reflexes are specific, i.e. characteristic of all members of this species. Conditioned reflexes are individual: some representatives of the same species may have them, while others may not. Unconditioned reflexes are relatively constant; conditioned reflexes are non-permanent and, depending on certain conditions, can develop, consolidate or disappear. 115

Unconditioned reflexes are performed in response to adequate stimuli applied to a specific receptive field. Conditioned reflexes can be formed in response to any irritation of any receptive field perceived by the body. Conditioned reflexes are produced based on unconditional ones. They are primarily a function of the cerebral cortex. Unconditioned reflexes can be carried out at the level of the spinal cord and brain stem. Age features of conditioned reflexes. Conditioned reflexes in the neonatal period are very limited. Already in the first days of a child's life, it is possible to note the formation of a natural conditioned reflex at the time of feeding, expressed in the awakening of the child and increased motor activity. With a strict feeding regimen for 6-7 days, in infants the manifestation of this reflex occurs as early as 30 minutes before feeding, and the gas exchange increases before eating. From the middle of the first month of life, conditioned reflexes to various first – signal stimuli arise: to light, sound, olfactory stimulation. The rate of formation of conditioned reflexes in the first month of life is very small and increases rapidly with age. In children of preschool age, the role of the imitative and play reflex increases significantly. So while playing with dolls, children precisely copy gestures, words, manners of educators and parents. The rate of formation of conditioned reflexes in children over 10 years old and in adults is almost the same. In adolescence, the formation of temporary connections is hampered, and the rate of formation of conditioned reflexes decreases. Therefore, the peculiarities of higher nervous activity require an attentive attitude, a well thought – out organization of the educational process. The interaction of excitation and inhibition in the central nervous system ensures the accuracy and flexibility of higher nervous activity. In its outward manifestation, inhibition is the opposite of excitation. There is an unconditional and conditional inhibition. External inhibition. Unconditional inhibition is called external or inductory and it is characteristic of all elements of the nervous system and is innate. This type of inhibition is a process of emergency atenuation or termination of individual behavioral reactions under the action of stimuli coming from the external or internal environment. External inhibition often occurs in the conditions of a person's daily life. This is a constantly observed decrease in activity, indecisiveness of actions in a new, unusual environment, a decrease in the 116

effect of a particular activity under the action of any unusual extraneous stimuli. For example, painful irritation or a signal about it dramatically inhibits food conditioned reflexes. In school practice, conditioned reflexes of children are associated, for example, with writing; they are inhibited if the students are affectted by any sufficiently strong external stimulus. Such an irritant can be, for example, a clap of thunder, a loud shout of a teacher, a feeling of hunger, stuffiness, etc. External inhibition includes a dimming and permanent inhibition, as well as limiting inhibition. Fading inhibition. Every unexpected foreign stimulus contains information that is new to the body, and an approximate reflex is performed for its fuller perception. At the time of occurrence of this reflex, two reflexes are inhibited. Repeated irritation causes an approximate reflex of lesser intensity, which then disappears due to habituation to this irritation. Permanent inhibition is characterized by the constancy of its effect on a particular inhibitory reflex, for example, defensive unconditioned reflexes to various harmful irritations, including pain. Under natural conditions, at certain periods of life, sexual behavior turns out to be stronger and inhibits other types of reflexes (in spring, students learn worse than in the fall, which is explained by the manifest of sexual dominant). Limiting (guarding) inhibition. If you increase the intensity of any irritation, then the effect caused by it increases. However, further intensification of irritation will lead to fading or complete disappearance of the effect. The basis of this result is not fatigue, but limiting inhibition. The limiting inhibition also develops with the simultaneous action of several non-strong stimuli, when the total effect of the stimuli begins to exceed the limit of the efficiency of the cortical cells. Unconditional inhibition is manifested in the first days of a child's life. A child does not eat and cries if he feels pain. Due to the low functionality of the nerve cells, infants easily fall into limiting inhibition and sleep. At the age of 3 to 5 years, external inhibition develops to play such a large role, as it was before. Internal inhibition is becoming increasingly important, although the strength of the resulting inhibition effect is still low. 117

Internal inhibition. It manifests in the form of delay, extinction, elimination of conditioned reactions. Conditional inhibition is characteristic mainly of the higher parts of the nervous system. It arises within the central nervous structures of the conditioned reflexes themselves, and hence it received its name, the internal inhibition (that is, not induced from the outside). Conditional inhibition depends on the physiological strength of the unconditioned reflex, which supports a positive conditioned signal, and develops when stimuli are not supported. A retarded conditioned reflex can spontaneously recover and this is important for education at an early age. There are four types of conditional inhibition: extinguishing, differential, conditional inhibition, retardation inhibition. Extinguishing inhibition occurs when the conditioned stimulus is presented several times without enhancement. It is a very common phenomenon and has a great biological significance, because it helps a person to get rid of a habit. Fading of it can be attributed to the temporary loss of labor skill, the fragility of knowledge of educational material, if it is not fixed by repetition. Differential inhibition develops when stimuli that are close in properties to the reinforced signal are not reinforced. It leads to a difference between a positive (reinforced) signal and a negative (differentiated) signal. In this case, the work of internal inhibition is aimed at "not confusing" similar stimuli. Differential inhibition serves as the basis for the analysis of stimuli acting on the organism, distinguishing objects and phenomena of the surrounding reality. The process of training and education is based on the development of differential inhibition. It has an extremely important significance for learning the letters and sounds of the native and foreign tongues, in the lessons of mathematics, singing, etc. The time for the beginning of distinguishing stimuli in children is different. It depends on the "age maturity" of the cerebral cortex, previous preparation, degree of fatigue of the body. A conditioned inhibition is formed when a combination of a positive conditioned signal and a corresponding stimulus is not confirmed. If a child has a positive conditioned reflex to the teacher, then he is assimilates the material well, shows the interest in the subject, while if there is no contact between the teacher and the student, a negative 118

attitude towards the teacher is transferred to the subject that results in poor performance. In the development of retardation or delay, the reinforcement of the corresponding unconditioned reflex is not canceled, but signifycantly postponed from the beginning of the action of the conditioned stimulus. Only the last period of the signal is reinforced, and the significant period that precedes it, is deprived of reinforcement. A typical example of the adaptive value of retarding inhibition may be the conditional secretion of gastric juice. Due to retardation, useless and harmful filling of an empty stomach with an acidic gastric juice is avoided; the gastric juice meets the food entering the stomach in time, ensuring its full digestion. Conditional inhibition in infants is already beginning to develop, but due to the weakness of the excitatory processes, the strength of the orienting reflex, this process is difficult, and there are significant individual differences. In the second half of the first year of life, the child begins to develop retarded inhibition. Sleep and dreams. Sleep is a condition characterized by a significant weakening of ties with the outside world. Sleep plays the role of the recovery process. During sleep, the intensity of metabolic processes, the muscle tone decrease, as well as the heart rate. Sleep is necessary for normal mental work. This is not just rest, but active recovery of the body. Sleep and inner inhibition are a single process by their very nature. However, internal inhibition during wakefulness covers only certain groups of cells, and during sleep, it spreads through the cortex of the hemispheres and to the lower parts of the brain, providing the necessary rest and the possibility of recovery. Sleeping consists of two large stages, which are regularly and cyclically replaced: 1) sleep is slow, lasting 60-90 minutes and 2) sleep is fast (paradoxical), that lasts 10-20 minutes. Slow sleep is also not well organized and in turn, it consists of several phases. For the fast sleep, dreams are characteristic – those dreams that we remember after waking up. At this time, there is a movement of the eyeballs, a reduction in facial muscles, increase in breathing and heart rate, and an increase in arterial pressure. The brain during paradoxical sleep works very intensely, recalling the wakefulness period with its activity. Slow sleep is accompanied by a decrease in vegetative tonus, pupils are 119

constricted, and skin becomes pink, sweating increases, tear formation and salivation decrease, and the activity of the cardiovascular, respiratory, digestive and excretory systems also decreases. Slow sleep is also characteristic of slow movements of eyes. Fast sleep is obviously an older acquisition in human evolution, since deeper brain structures are responsible for it. In young children, fast sleep dominates, and only with age does the proportion of slow sleep increase. Slow sleep is associated with younger evolutionary structures of the brain, is more complexly organized and more difficult to regulate. In an adult, monophasic sleep is observed (one time per day) or differently, in a child, polyphasic sleep. The newborn sleeps 21 hours a day, children younger than 10 years – up to 14 hours, after 10 years – 7-8 hours. Not to sleep more than 3-5 days is impossible. Subjective sensations at 40-80 – hour sleep deprivation is very unpleasant. There is an emotional imbalance, fatigue, crazy ideas, impaired vision, and disorders of vestibular function. After 90 hours of sleep deprivation, hallucinations appear. A person sleeps on average 8 hours a day, which represents approximately one third of the day, and, therefore, one third of his life, i.e. of 75 years a human sleeps 25 years. Memory. The formation of conditioned reflexes is possible due to a special property of the brain – memory. Memory is the ability of the body on perceiving an impact from outside to consolidate, preserve and subsequently reproduce the changes in the functional state and structure caused by such stimulus. Information signals first act on the senses, causing changes in them, which, as a rule, is held for no more than 0.5 seconds. These changes are called a sensory memory – it allows a person to maintain, for example, a visual image while blinking or watching a movie, perceiving the unity of the image, despite the changing frames. In the process of training, the duration of this type of memory can be extended to tens of minutes. In this case, we speak about eidetic memory when its character is controlled by consciousness (at least partially). Besides the sensory memory necessary for the storage of information, there is a short-term memory, which allows you to operate information for tens of seconds. It is based on a temporary increase in conductivity in synapses and electrophysiological mechanisms associated with multiple circulation of pulses through a closed system 120

of neurons. The unnecessary material is erased when it is replaced with a new information. The most important and significant part of the information is stored in the long-term memory, which provides these functions for years and decades. Long-term memory is formed with the indispensable participation of reinforcement systems, i.e. it has a conditioned reflex nature. Long-term memory is formed based on the synthesis of molecules – nucleic acids, proteins – and takes place with the participation of the genetic apparatus of the nerve cells, as a result of which the changes in the membranes of neurons and interneuron connections occur. Memorization of underlying memory can occur unconsciously and consciously. In the first case, it is difficult to reproduce information in the usual way; in the second case, it is easier. The mechanism of memorization can be imagined as a chain: the need (or interest) – motivation to fulfill – concentration of attention – organization of information – memorization. In this case, the break of any part of the chain affects memory. In addition, in connection with the peculiarities of perception, a conception memory may predominate (visual, auditory, etc.). In connection with the functional asymmetry of the brain, it is possible to distinguish the verbal form of memory and the conception memory; therefore, in the junior school, for example, the illustrative and emotional flow of information has a greater significance, while in the senior school – the logical one. Children's memory is photographic. The child will immediately correct an adult, who has missed a detail or some details in a fairy tale. The child usually associates on a random basis distant objects or events. In addition, it is necessary that the child's memory acquired a readiness to memorize. The student must know in advance, when and how the memorized material will be useful to him. Memory disorders (weakening, strengthening, distortion, amnesia, etc.) can occur due to age – related changes in mental activity, physical and emotional stress (fatigue, stress), brain injuries, and a number of mental diseases (psychosis). The first and second signal systems. The considered patterns of reflex activity are common both for higher animals and for man, since they reflexively respond to specific signals of the external environment (sound, light, temperature, etc.). For animals, this is the only signaling 121

system, and for humans it is only the first. The higher nervous activity of man fundamentally differs from the higher nervous activity of animals due to labor and articulate speech. The word for humans has acquired the meaning of a signal and constituted a specifically human second signal system. It became the same conditioned stimulus as all the others that make up the first signal system. During the first months of life, the child manifests conditioned reflexes that are not related to the semantic meaning of words. Only at the end of the first year of a child's life does the word acquire meaning for him. From this point on, the child's brain becomes a step higher than that of animals. Through articulate word, the child contacts the social, purely human environment. The emergence of the second signaling system, associated with verbal signaling, radically changed the higher nervous activity of a human. Irritants of the second signaling system are words that provide a higher degree of generalization than the stimuli of the first signaling system. The presence of the second signaling system contributes to the implementation of any conditioned-reflex reaction and becomes the foundation of all human mental activity, because man thinks in words. The child begins to consciously master the tongue only at school when he becomes acquainted with the highest form of its manifestation – written speech. In preschool children, vocabulary makes up 300-500 words, in primary school children – 3000-4000 words, and in an adult person – 11000 or more words. The development and improvement of the second signaling system occurs continuously in the process of training and education. For its normal functioning, the interaction of various areas of the cerebral cortex is necessary. When these relationships are broken, various pathological phenomena occur. Thus, with painful changes in the left hemisphere, in which speech and writing centers are located in the frontal lobe, certain words are forgotten, the opportunity to pronounce them correctly is lost, and the writing mechanism is broken. The activity of the entire cerebral cortex is in a complex relationship with the sub-cortex, with the second signal system acting as the "highest regulator of behavior", so it can suppress and restrain defensive, nutriational, sexual, and painful reflexes.

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Speech is a form of communication with the help of sounds and visual signs. By I.P. Pavlov, word is a "signal of signals", it performs the function of "doubling the world", and provides the transfer of experience of previous generations. Speech functions are as follows: – Communicative function – speech as a means of communication gives the listener verbal and non-verbal information; – Regulatory function is external and internal speech as a means of regulating body functions and behavior. Conceptual function – speech as an instrument of abstract thinking, a means of expressing thoughts, one of the mechanisms of intellectual activity. Programming function – the construction of semantic schemes of speech patterns, based on internal programming, carried out with the help of internal speech. There are peripheral and central mechanisms of speech. Peripheral speech mechanisms: – The mechanism of phonation is localized in the larynx. Its physical basis is the oscillation of the vocal cords. – The mechanism of articulation ensures the formation of vowels and consonants. The physical basis of articulation is the resonance of cavities in a fixed or variable configuration. Central speech mechanisms: – Mechanisms of speech perception are the auditory center of speech – Wernicke's area, the optical center; – Speech reproduction mechanism is Broca's center. In the process of evolution of the animal world, at the stage of development of the Homo sapiens species, a qualitative modification of the first signal system occurred, providing adaptive behavior. It is due to the emergence of the second signal system, the emergence and development of speech, the essence of which lies in the fact that in it the signals acquire a new property of conditionality, stimuli were converted into signs in the truest sense of the word. In contrast to the conditioned reflexes of animals, reflecting the surrounding reality through specific visual, auditory, olfactory and other signals, human speech reflects the surrounding reality through generalizing abstract concepts expressed in words. Therefore, I.P. Pavlov called it the second signal system of the human brain. 123

Under the second signal system I.P. Pavlov understood the nervous processes that occur in the cerebral hemispheres because of the perception of the signals of the surrounding world in the form of speech designations of objects and phenomena of nature and society. The word perceived by a human as heard (auditory analyzer), as written (visual analyzer) or as a pronounced signal (motor analyzer). In all cases, these stimuli are combined with the meaning of the word. Words acquire meaning because of the formation of a strong bond in the cortex of the cerebral hemispheres between the excitation centers that occur under the action of specific objects of the surrounding world and the excitation centers that occur when pronouncing words denoting specific objects or actions. Because of the formation of such bonds, words can replace a specific irritant of the environment and become its symbol. The word, as a signal of signals, makes it possible to escape from specific objects and phenomena. The development of verbal signaling made it possible to generalize and distract, which is reflected in the phenomena characteristic of a human – thinking and formation of concepts. In children of school age, the second signaling system intensively develops, but during puberty, it loses its value. The dominant role is acquired by the first signal system. During this period, it is necessary to use more visual aids, more concrete, actions at the lessons. Boys aged 13-15 years and girls aged 11-13 years have a slowed down speech that becomes stereotypical, and the answers are extremely laconic. Therefore, for the full answer of the student, the teacher should ask additional questions to determine the level of his knowledge. Consciousness is called the highest, peculiar only to man form of reflection of objective activity. It represents the unity of mental processes that are actively involved in the human understanding of the objective world. Consciousness arises in the process of labor, social and production activities of people and is inextricably linked with speech. Thinking is the process of human cognitive activity, characterized by a generalized and mediated reflection of the external world and internal experiences. The first stage in the organization of thinking in children consists in building sensory-motor circuits (up to 2 years). A sensory-motor 124

scheme is the execution of an organized sequence of actions that constitute a certain form of behavior (walking, eating, speaking, etc.). It is connected not only with the biological evolution of man, but also with his social development. The second phase (a period of 7-10 years) is characterized by the ability to reason and use specific concepts related to actual events. At the third phase, the ability to formal operations, to the evaluation of hypotheses appears (11-15 years). It is believed that during this period the formation of bonds of the frontal cortex with other parts of the brain is completed. The mental modeling of various events by a person is the essence of his thinking. A person assesses the actions leading to the goal set, the conditions that lead to a successful result. Under the ability to work, the ability of a person to develop a maximum of energy and, economically spending it, to perform work efficiently and effectively is understood. Fatigue is a set of changes that occur in the body during the period of work and lead to the impossibility of its continuation. The biological role of fatigue is extremely high. Firstly, it has a protective function, protecting the body from exhaustion during too long or too intense work. Secondly, a repeated fatigue, not brought to an excessive value, is a means of increasing the functional capabilities of the body. In the whole organism, fatigue primarily occurs in the central nervous system. At the same time, certain changes are taking place on the periphery, i.e. in the actual working bodies – the muscles. There are three degrees of fatigue. 1. It is manifested in the reduction of mental and physical performance, the emergence of motor anxiety, development of lethargy and drowsiness, loss of attention and susceptibility. This suggests the inhibition of orienting reflexes, which are always associated with the novelty of the stimulus. 2. There are headaches; there is a further weakening of attention in the classroom, loss of appetite, sleep disturbance. 3. It manifests in sleep disorders, increased headaches, irritability, and a sharp drop in efficiency, reduced body resistance to infectious diseases. Overwork, as opposed to fatigue, is already a long and profound decrease in working capacity, accompanied by disruption of the life support systems and requiring a long rest, and in some cases, special therapeutic measures. 125

Both fatigue and overwork in children appear faster than in adults, which is explained by the peculiarities of the central nervous system. At the same time, the causes of fatigue in younger schoolchildren are somewhat different from those in middle and senior schoolchildren. Fatigue in the students of primary school arises primarily because schoolchildren must master three basic school skills: writing skills, reading skills and long-term fixed sitting skills. A skill is understood as the ability to perform a particular action, fixed by repetition (exercise). The transition from skill to skill consists in the formation of stable and strong bonds in the central nervous system. In the process of forming a skill, the actions accelerate, the action becomes more accurate and more economical; a number of activity elements is automated. In order to prevent the growth of fatigue, it is necessary to organize training activities so that children could move from mental activity to physical activity and from the latter to mental activity. The excitement of new foci in the cortex leads to the fact that the centers that were excited during the previous type of work are inhibited. This leads to the restoration of their performance. A large role in reducing children's fatigue is played by positive emotions, such as joy, delight. Negative emotions, such as resentment, fear, lead children to the state of oppression, which creates the prerequisites for rapid fatigue. The performance of students of all ages at the first lesson is low: there is a process of starting the educational work after a period of night rest. At the first lesson, it takes the student10 minutes to switch into work, at the next one – 5 minutes. The duration of stable work for younger students is 15-20 minutes, for middle school age – 2530 minutes, for high school students – 30-35 min. The most rational change is 10-15 minutes. The highest performance during the school day is reached at the second and third lessons. Younger schoolchildren already at the fourth lesson have a noticeable decrease in working capacity, which is likely to be protective. For middle and high school students, a similar reaction occurs at the fifth and sixth lessons, respectively. That is why at the last lessons mental work turns out to be unproductive, and for some students it even becomes a factor causing mental stress. The analysis of the nature of students' performance suggests that it is 126

inappropriate to put two or even three difficult lessons in a row, and it is better to alternate difficult subjects that require considerable mental effort (mathematics, foreign language, chemistry, physics) with mostly physical activities associated with writing or recording (Russian, foreign language) or with a predominant explanation of the teacher (history, geography), etc. During the school week, there are also regular changes in the activity of the physiological systems of the body and the performance of the student. On Monday, this performance is relatively low after Sunday holiday. As for the schedule of training sessions for the week, it is should be based on the equal distribution of load on the days in the same pattern that was established for a particular day. With a five-day weekly schedule, one two-day plateau can be provided with optimal performance on Wednesday and Thursday. The main stages of the development of higher nervous activity. The lower and higher nervous activity of the child is formed because of the morphological and functional maturation of the entire nervous apparatus. The nervous system, and with it the higher nervous activity in children and adolescents, reaches the level of an adult by about 20 years. The entire complex process of the development of a person's HNA is determined by both hereditarily and other biological and social factors of the external environment. The external environment plays a leading role in the postnatal period, therefore the family and educational institutions bear the main responsibility for the development of human intellectual abilities. HNA of a child from birth to 7 years. A child is born with a set of unconditioned reflexes, reflex arcs of which begin to form at the 3rd month of fetal development. Then the first sucking and breathing movements appear in the fetus, and the active movement of the fetus is observed at the 4th-5th month. By the time of birth, the child forms the majority of congenital reflexes, which ensure the normal functioning of the vegetative sphere. The possibility of simple food-conditioned reactions arises already on the 1-2 day and by the end of the first month of development conditioned reflexes are formed from the motor analyzer and vestibular apparatus. From the 2nd month of life, auditory, visual and tactile reflexes are formed, and by the 5th month of development, all the main types 127

of conditioned inhibition are developed in the fetus. Of great importance in improvement of the conditioned reflex is training of the child. The sooner the training has begun, that is, the development of conditioned reflexes, the faster their formation is in future. At the end of the 1st year of development, the child distinguishes relatively well the taste of food, smells, the shape and color of objects, distinguishes voices and faces. Movements are significantly improved and some children begin to walk. The child tries to pronounce individual words and conditioned reflexes to verbal stimuli are formed. Consequently, already at the end of the first year, the development of the second signaling system is in full swing and its joint activity with the first one is being, formed. In the 2nd year of life, all types of conditioned reflex activity are improved, the formation of the second signal system continues, the vocabulary increases significantly; stimuli or their complexes begin to cause verbal reactions. Already in a two-year-old child, the words acquire a signal meaning. The 2nd and 3rd year of life are distinguished by lively orientation and research activities. This age of the child is characterized by the "objective" nature of thinking, that is, the decisive significance of muscular sensations. This feature is largely associated with the morphological maturation of the brain, since many motor cortical zones and skin-muscular sensitivity zones reach a rather high functional usefulness by the age of 1-2 years. The main factor stimulating the maturation of these cortical zones is muscle contraction and high physical activity of the child. The period of up to 3 years is also characterized by the ease of formation of conditioned reflexes to a wide variety of stimuli. A remarkable feature of a 2-3-year-old child is the ease of developing dynamic stereotypes is successive chains of conditioned reflex acts, carried out in a strictly defined, fixed in time order. The dynamic stereotype is a consequence of a complex systemic response of the body to a complex of conditioned stimuli (a conditioned reflex to time – food intake, sleep time, etc.). The age from three to 5 years is characterized by the further development of speech and the improvement of nervous processes (their strength, mobility and balance increase), the processes of internal inhibition become dominant, but delayed inhibition and conditioned inhibition are difficult to develop. 128

By 5-7 years, the role of the signal system of words increases even more, and children begin to speak fluently. This is because only by the age of seven years of postnatal development the material substrate of the second signaling system, the cerebral cortex functionally matures. HNA of children from seven to 18 years. The younger school age (from 7 to 12 years old) is a period of relatively "calm" development of HNA. The strength of the processes of inhibition and excitation, their mobility, balance and mutual induction, as well as the reduction of the force of external inhibition, provide opportunities for the child to learn. Only when learning to read and write the word becomes the subject of the child's consciousness, more and more moving away from the images, objects and actions connected with it. A slight deterioration in the processes of HNA is observed only with the start of the processes of adaptation to school. Of particular importance for teachers is adolescence (from 1112 to 15-17 years) period. At this time, the equilibrium of the nervous processes is disturbed, excitation becomes more powerful, the growth of mobility of the nervous processes slows down, and the differrentiation of conditioned stimuli deteriorates significantly. The activity of the cortex weakens, as well as the second signaling system. All functional changes lead to mental imbalance and conflict behavior of the teenager. Senior school age (15-18 years) coincides with the final morphological and functional maturation of all body systems. The role of cortical processes in the regulation of mental activity and functions of the second signal system is increasing. All properties of the nervous processes reach the level of an adult, that is, the HNA of older students becomes orderly and harmonious. Thus, for normal development of HNA at each separate stage of ontogenesis, it is necessary to create optimal conditions. Types of higher nervous activity. As you know, different people in different life situations behave differently. This is explained by the fact that the mental activity of each person is purely individual. Even in ancient times, scientists tried to classify people by temperament, but I.P. Pavlov proposed the first scientific classification. According to this teaching, the nervous system is characterized by three main properties: force, balance and mobility of the processes of excitation and inhibition. The nature of the interaction of these three properties of the 129

nervous system determines the individual characteristics of the higher nervous activity of man, his performance and behavior. I.P. Pavlov identified four types of higher nervous activity: a strong unbalanced type; strong balanced, agile type; strong balanced, sedentary, or inert type; and weak, low and excitable type. Strong unbalanced type. People of this type are distinguished by high emotional excitability, hot temper, affects, they move impulsevely, and speak quickly. They have a slight formation of conditioned reflexes, but inhibition significantly is weakened, the processes of excitation prevail over the processes of inhibition. Children of this type do not have enough assiduity, perseverance in work. They are very mobile, excitable, speak loudly, inadequately actively react even to weak unfavorable irritations, show little discipline, and are often aggressive. Among such children there are very capable, emotional, and temperamental. Another group of children of this type is characterized by aggressive behavior. They are very hot-tempered, their outbursts of anger are frequent, but these do not last long. Finally, the third group of a strong unbalanced type – these are difficult children. Their inhibitory processes are so lowered that they are unable to suppress their instincts and often violate the aesthetic standards of behavior. The influence of parents and teachers becomes a new irritant and causes an even more developed process of excitation, reaching aggressiveness. Strong balanced, mobile type. Speech in such people is fast, but smooth, with mobile facial expressions and gestures, characterized by a rich vocabulary. They are usually sociable and emotional, cheerful, initiative and quickly adapt to unfamiliar surroundings. They are characterized by a rapid formation of conditioned reflexes, the strength of which is significant, the processes of excitation and inhibition in them are strong enough, balanced and have good mobility. Children of this type study successfully, are disciplined, have well-developed speech, with a rich vocabulary, and are distinguished by high performance. Strong balanced, sedentary (inert) type. In people of this type, the processes of excitation and inhibition are strong and balanced, but the transition from one type of activity to another is difficult for them, and conditioned reflexes are formed slowly but firmly. They are sedentary, assiduous and quite persistent in overcoming difficulties. 130

Such children have a calm speech, correct, with a sufficient vocabulary, but without excessive mimics and gestures. They are successfully engaged in school, and conscientious in the performance of tasks, sedentary, diligent in class, disciplined. Weak, poorly excitable type. Conditional bonds in people of this type are formed more slowly; faded reflexes are restored also slowly, the control of the cortex over unconditioned reflexes and emotions is less pronounced. They are active and eager to overcome difficulties. For the formation of conditioned reflexes in children of this type, a large number of combinations with an unconditioned stimulus is required. Therefore, conditioned reflexes are formed slowly. Strong or prolonged irritations cause in these children transcendental inhibition, they get tired easily. Outside stimuli easily cause external inhibition in them. However, the type of higher nervous activity of a child cannot be considered as something unchangeable. It is distinguished by considerable plasticity, relatively small functional stability, and this creates favorable conditions for the directional formation of typological features in the educational process. Typological features of the child's HNA. N.I. Krasnogorsky, studying the child's HNA based on strength, balance, mobility of nervous processes, interrelations of the cortex and subcortical formations, the relationship between signaling systems, identified four types of nervous activity in childhood. 1. Strong, balanced, optimally excitable, fast type. It is characterized by a rapid formation of strong conditioned reflexes. Children of this type have a well – developed speech with a rich vocabulary. 2. Strong, balanced, slow type. In children of this type, conditional bonds are formed more slowly and their strength is less. Children of this type learn to speak quickly, but they have a somewhat slow speech. They are active and persistent in performing complex tasks. 3. A strong, unbalanced, excessively excitable, impetuous type. Conditioned reflexes in these children quickly fade away. Children of this type are distinguished by high emotional excitability, hot temper. Their speech is fast with occasional screams. 4. Weak type with reduced excitability. Conditioned reflexes are formed slowly, are unstable, speech is often slow. Children of this type 131

cannot tolerate strong and prolonged irritation and they easily get tired. Significant differences in the basic properties of nerve processes in children of different types determine their different functionalities in the process of training and education, but the plasticity of the cells of the cortex of the big hemispheres, their adaptability to changing environmental conditions is the morphological and functional basis of the transformation of the type of HNA. Since the plasticity of the nervous structures is especially great in the period of their intensive development, it is especially important to apply in childhood a pedagogical influence, correcting typological features. Questions for self-control 1. What is the general scheme of the structure of the function of the central nervous system? 2. What are the features of humoral and nervous regulation? 3. What formations in the nervous system are called synapses? What is the structure of the synapse? Name the types of synapses. 4. Which divisions does the brain stem include? 5. What are the functions of the medulla? 6. What is meant under the higher nervous activity of the student? 7. What are conditioned reflexes? 8. What are the rules for the formation of conditioned reflexes? 9. Explain the physiological mechanism of the formation of conditioned reflexes. How does it relate to the learning process? 10. What are the conditions for the formation of conditioned reflexes? 11. What reflexes are called natural, the reflexes of the first, higher order, unbreakable reflexes? 12. Describe the main types of inhibition of conditioned reflexes in schoolchildren. 13. What is a dynamic stereotype? What is its meaning for the schoolchild and preschooler? 14. What are the types of inhibition of conditioned reflexes? What is the significance of differentiating inhibition in the schoolchild's learning? What is a "conditional inhibition"? 15. What is the first and second signal system? 16. What types of HNA did I.P. Pavlov single out?

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PHYSIOLOGY OF SENSOR SYSTEMS AND AGE FEATURES Features of sensory function in children and adolescents. Elementary reflex activity of a person, his complex behavioral acts and mental processes depend on the functional state of his sense organs: sight, hearing, smell, taste, somatic and visceral sensitivity, with the help of which the perception and analysis of an infinite flow of information from the surrounding material world and the internal environment is delivered to a human. Without this information, the optimal organization of the most primitive functions of the human body and the higher mental processes would not be possible. The sensory, auditory, visual, vestibular, olfactory and somatosensory systems are distinguished among the sensory systems of the body. The receptors of the latter are located in the skin and perceive touch, vibration, heat, cold, pain. There is also a proprioceptive system, which includes proprioceptors that perceive movement in the joints and muscles. The study of receptors located in all internal organs, the paths of conducting and processing the signals coming from them, gave reason to speak of the visceral sensory system, which perceives various changes in the internal environment of the body. Different sensory systems begin to function at different periods of ontogenesis. The vestibular analyzer as phylogenetically the most ancient formation matures in the prenatal period. Reflex acts associated with the activity of this analyzer (when the body turns, changes the position of the extremities) are observed in fetuses and premature babies. In addition, the skin analyzer ripens early. The first reactions 133

to skin irritation are observed in the embryo at 7.5 weeks. Already at the 3rd month of the child's life, the parameters of skin sensitivity almost correspond to those of an adult. The analyzer is a section of the nervous system consisting of sensory nerve cells (receptors), intermediate and central nerve cells, and nerve fibers connecting them. Analyzers are the systems for entering the information into the brain and for analyzing this information. The work of the analyzer begins with the perception of chemical and physical energy that is external to the brain, transformation of it into neural signals. Excitation from the receptor along the nerves enters the cerebral cortex, where in the corresponding zone there is a differentiation of stimuli and visual, sound and other sensations arise. There are visual, auditory, gustatory, somatosensory, visceral analyzers, and analyzers of balance, touch, and smell. They provide a person with the information that allows him to navigate in constantly changing environmental conditions. Adequate reactions to taste analyzer irritations are observed from the 9-10th day of life. Differentiation of basic nutrients is formed only at the 3-4th month of life. Up to 6 years of age, sensitivity to taste irritants increases and at school age does not differ from the sensitivity of an adult. The olfactory analyzer functions from the moment of the birth of the child, and the differentiation of odors is observed at the 4th month of life. The maturation of sensory systems is determined by the development of bonds of the senses. Peripheral bonds are formed at the time of birth. Later others form the peripheral part of the visual analyzer – the retina, its development ends by 6 months of life. Myelination of nerve fibers during the first months of life provides a significant increase in the rate of excitation and, therefore, the development of the conductive part of the analyzer. Later other cortical bonds of the senses are formed. Their maturation determines the characteristics of the functioning of sensory systems in childhood. The cortical bonds of the auditory and visual sensory system complete their development most lately. In studying the movement of the eyes of a child, it was established that he is able to perceive the elements of the displayed images from the moment of birth. It is believed that the individual elements of the 134

image in infancy are identified as a holistic subject. This is evidenced by the data showing that infants who developed a conditioned reflex to a holistic geometric figure, also responded to its components, presented separately, and only from 16 weeks, the child perceived a holistic figure that became a stimulus to the conditioned reaction. As the cortical neurons and their bonds mature, during the first years of a child's life, the analysis of external information becomes more subtle and differentiated, and the process of identifying complex stimuli is improved. The period of intensive maturation of the systems is the most plastic. The maturation of the cortical bond analyzer is largely determined by the incoming information. It is known that if we deprive the body of the newborn of the flow of sensory information, the nerve cells of the projection cortex do not develop; in a rich in sensory information environment, the development of nerve cells and their contacts occurs most intensively. Hence, the importance of sensory education in early childhood, that is, sensory information, is important not only for the organization of internal organs and behavior, but is also an important factor in the development of a child. The functional maturation of sensory systems continues in other age periods, since other cortical zones (associative), which mature over a long period of development, including adolescence, are also involved in processing of incoming information. The gradual maturation determines the peculiarity of the process of perception of information at school age. Thus, the perception of complex visual stimuli becomes identical to those of an adult by the age of 11-12. The organs of vision and hearing are especially important for the normal physical and mental development of children and adolescents. This is because the vast majority of all information from the outside world (approximately 90%) enters our brain through the visual and auditory channels. Visual analyzer. The peripheral part of the visual analyzer is the eyeball. In children, it has a spherical shape; in adults, it is slightly elongated. Three shells form the walls of the eyeball: the outer shell is the white of the eye, the middle shell – a vascular net and the inner one is the retina. The retina is a part of the brain, carried to the periphery; it is an inner membrane of the eye, which has a multilayer structure. Its outer layer, the most distant from the pupil is pigmented. It is formed by the pigment epithelium and contains the fuchsine pigment. 135

The latter absorbs light, prevents its reflection and scattering, which contributes to the clarity of vision. The retina contains light – sensitive receptors shaped as rods and cones. The rods are responsible for the perception of light, twilight vision, the cones – for color perception, day vision. So, the light ray first passes through the light-refracting medium of the eye – the cornea, the lens and the vitreous body, after which the inverse reduced image of the object is formed on the retina. Along the optic nerve, excitation is transmitted to the visual centers located in the occipital lobe of the cerebral cortex (central part of the analyzer), where irritation is distinguished (Figure 13). Suspensory ligaments

Sclera Tunics

Choroid Aqueous humor

Retina

Fovea centralis

Cornea Iris Lens Ciliary muscle

Optic nerve

Conjunctival sac

Optic disc

Figure 13. The eye. Note the three tunics, the refracting parts of the eye (cornea, aqueous humor, lens, vitreous body), and other structures involved in vision.

Of all light-refracting media, only the lens can change its curvature, while changing the angle of the rays passing through it, which allows getting a clear image on the retina of the objects at different distances from the eye. When a person looks into the distance, the image of objects focuses on the retina and they are clearly visible, but 136

the close objects are seen vaguely, because the rays gather behind the retina. To see both distant and close objects at the same time is impossible. The adaptation of the eye to clear vision is called accommodation. The mechanism of accommodation is the contraction of ciliary muscles, which alter the convexity of the lens. The lens is enclosed in a capsule, passing into the ligaments, and is constantly in a tense state, the ciliary muscles are innervated by the parasympathetic fibers of the oculomotor nerve. For a healthy eye, the farthest point of clear vision lies at infinity. It sees far off without accommodation, i.e. ciliary muscle contraction. The nearest point of clear vision is 10 cm from the eye. The pupil is a hole in the center of the iris, through which the light rays pass into the eye. It contributes to the clarity of the image, letting pass only the central rays and eliminating peripheral ones. The musculature of the iris changes the size of the pupil, regulating the flow of light that enters the eye. The change in the diameter of the pupil changes the luminous flux 17 times. In the iris, there are two types of muscle fibers: annular, innervating the parasympathetic fibers of the oculomotor nerve, and radial, innervated by sympathetic nerves. Parasympathetic fibers cause constriction of the pupil, sympathetic ones – its expansion. With emotions (rage, fear), or when excitement occurs, as well as in pain, the pupils dilate. This is a sign of a pat-hological condition, such as a pain shock. For viewing any items, eye movement is required. Six muscles attached to the eyeball perform it. These are two oblique and four rectus muscles – external, internal, upper and lower ones. Only the outer muscle turns the eye straight outward, and the inner one turns straight inward. The upper and lower muscles with the oblique one turn the eye not only up and down, but also inside. It has been revealed that some cones absorb red-orange rays as much as possible, other ones – green, and still others – blue rays. The three-component theory also explains such facts as consistent color images and color blindness. With the prolonged action of rays of a certain wavelength in cones, the corresponding photosensitive substance splits. Color blindness. It was discovered by the physicist Dalton in the 18th century, who himself suffered from this disease. This disease was 137

named after him. About 8% of men suffer from it. This is a genetic disease associated with the absence of certain genes in the unpaired X chromosome. It may be determined using color tables and it is important for some professions. There are three types of color blindness: 1. Protanopia is blindness to red, people do not perceive red color, and blue rays seem to them colorless. 2. Deuteranopia is blindness to green; people do not distinguish green from dark red and blue. 3. Tritanopia occurs rarely, blue and purple rays are not perceived. All these anomalies are well explained by 3-component theory. Each of them is the result of the absence of one of the three colorsensing substances located in cones. A complete color blindness may also be met. It occurs because of damage to the entire cone apparatus. All items are black and white. Since color has a wave energy nature, a person experiences its effect. The longest wavelength is red. It has the greatest impact on the retina, so we notice it before the others. Red color has a stimulating effect (pulse, blood pressure, breathing increase). Blue color has the opposite effect, it improves mental activity, reduces appetite (in nature there are practically no blue fruits). Therefore, it is recommended painting the walls of classrooms in blue, and dining rooms – in orange, which is an appetite stimulant. Light green color with a calming effect is suitable for rest rooms. If accommodation is disturbed, myopia or farsightedness may develop. With a strong refraction of light rays, they are focused in front of the retina due to the increased curvature of the lens or lengthening of the eyeball, which causes myopia. Farsightedness is caused by a weak refraction of light rays and their focus behind the retina. It occurs due to the shortening of the eyeball or flattening of the lens. The lens becomes less elastic with age, ligaments weaken and accommodation becomes weak. The nearest point of clear vision is moving away – this is senile farsightedness, although the length of the eyeball does not change. Visual impairment in both myopia and hyperopia is corrected by the selection of optical lenses.

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To maintain normal vision, a set of hygienic rules has been developed. The eye should be protected from mechanical stress, it is necessary to read in a well-lit room, keeping the book at a certain distance (up to 33-35 cm from the eyes). The light should fall from the left. When working in bright conditions, it is necessary to use light-shielding glasses, since bright light destroys light-sensitive cells. One should not read in a moving vehicle. In a lack of vitamin A, twilight vision is disturbed and so-called "night blindness" develops. Factors that impair vision are also nicotine, alcohol, drugs, and other toxic substances. The most favorable for sight and concentration of attention of students is a diffused light. Therefore, the source of artificial lighting should be equipped with a special light-scattering armature. Whatever the lighting in the classroom – natural, artificial or mixed, a number of general requirements are imposed on it. These requirements are sufficiency, uniformity, the absence of shadows in the workplace, the absence of glare, the absence of overheating of the room. The coloring of the walls, pupils' tables and the blackboard plays a major role in the illumination of classrooms. For walls, it is best to choose light yellow tones, reflecting about 60% of the light falling on them. It is best to paint the students' tables with a light green color and blackboards – with dark green. Such boards absorb a significant part of the light falling on them, contrasting with the notes and drawings made with chalk. Auditory and vestibular analyzers. An auditory organ consisting of the outer, middle and inner ear represents the peripheral part of the auditory analyzer. The first two sections perform auxiliary functions, and the perception of sound stimulation is carried out in the part of the inner ear, called the cochlea. The function of the outer ear, formed by the auricle and the external auditory canal, is to capture and conduct sound waves to the eardrum, which begins to oscillate in sync with them. In the middle ear, there is a transmission mechanism – three auditory ossicles form the hammer, the anvil and the stirrup, which successively interlock with each other. The inner ear is formed by a bone labyrinth located in the thickness of the temporal bone, in which, as in a case, there is a connective tissue webbed labyrinth, repeating mainly the outlines of the bone and filled with endolymph (Figure 14).

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Outer ear Ear canal Ossicles

Vestibule Oval Window

Semicircular canals

Cochlea

Middle ear Round Ear Window drum

Eustachian tube

Figure 14. The Anatomy of the Ear

Two sacks of the vestibule form the membranous labyrinth; three mutually perpendicular semicircular canals depart from one sack, and the cochlea – from the other one. The semicircular canals form the vestibular apparatus, not connected with the function of hearing, but providing orientation in space and balance. Information about the sound stimulus comes from the cochleae on both sides of the head to the auditory nuclei of both halves of the brain stem and into the auditory cortex of both hemispheres. Three auditory projection zones with complex inter-bonds are found in the cortex. After that, the information is transmitted to the nuclei of the lateral loop and the lower hillocks of the midbrain corpora quadrigemina (Figure 15). The peripheral end of the vestibular analyzer lays in the semicircular canals, the fibers from the vestibular receptors fall into the XIII nerve. From here, a smaller part of the fibers goes to the cortex of the worm of the cerebellum, and a large part ends in the anterior nuclei of the rhomboid fossa (4th cerebral ventricle). The nuclear zone of the vestibular analyzer is located in the temporal region. 140

Cochlea cross section Inner ear

Semicircular canals

Organ of Corti

Round Window Cochlea Outer hair cells

Inner hair

Figure 15. Cochlea and the organ of Corti.

The quality of hearing in children is lower than that in adults. It gradually increases up to 14-19 years. The threshold of hearing of speech also changes noticeably. In children of primary school age, it is higher than in adults. The ability to distinguish the height of tones depends on various factors, including congenital features. Musically gifted children already at an early age can not only distinguish the height of tones, but also accurately determine each of them. The highest hearing sensitivity in humans is observed in the frequency range from one to 4 kHz, the entire range extending from 12 Hz to 20 kHz. Starting from 35-40 years, there is an increase in hearing thresholds at high frequencies by about 80 Hz every six months. This is due to a decrease in the elasticity of the ear tissue. The absolute sensitivity of the ear is so great that a person is almost able to hear the 141

blows of air molecules on the eardrum and at the same time, the ear is able to withstand very strong intensity of the sound waves that cause vibration of the whole body, for example, during explosions. Taste analyzer. Taste buds are located on the tongue, as well as on certain areas of the soft palate and the posterior pharyngeal wall. These receptors are called taste buds. Some taste buds perceive a sweet taste, other ones – bitter, the third ones – sour, and the fourth – salty taste. These taste cells are the peripheral portion of the taste analyzer. The conductor division consists of fibers of the trigeminal, vagus, and glossopharyngeal nerves. The impulses arrive at the nuclei of a single path in the medulla oblongata, then into the ventral nucleus of the optic lobe and into the posterior central gurus of the new cortex. Olfactory analyzer. In addition, olfactory irritations are involved in determining what is called food taste in everyday life. The sense of smell are formed by receptors located in the epithelium of the upper part of the nasal cavity (peripheral part of the analyzer). Along the processes of the olfactory cells that make up the olfactory nerve (conductor part), the excitation is transmitted to the olfactory zone of the temporal cortex (central part of the analyzer). Stimulators of olfactory receptors are substances that are in a gaseous state in the inhaled air. During the meal, the olfactory sensations complement the taste. Skin analyzer. Skin receptors perceive several types of sensations. It is pain, heat, cold, touch and pressure. Each of these sensations is perceived by specific receptors. Touch and pressure receptors are called tactile receptors. Closer to the surface of the skin there are pain and tactile receptors, and the temperature receptor lies deeper. The receptors are embedded in the skin and serve as the peripheral part of the skin analyzer. In the muscles, tendons, ligaments there are proprioceptors, represented by muscle and tendon spindles (this is the peripheral part of the motor analyzer). The central part of the skinmuscular sensitivity is the central regions of the big hemispheres. Impulses from temperature and pain receptors enter the posteriorcentral regions of the cerebral cortex. The body is in contact with the external environment through the skin. The skin, in addition to the sensitive function, performs protective, excretory, and thermostatic functions. You should know that the skin of the child is thinner than the skin of adults and less resistant to 142

damage, so the issue of hygiene of clothes is very important. The lower part of the back (kidneys), throat, and legs should be especially protected from cold, in girls – the lower part of the body. To increase the body's resistance to adverse climatic conditions, developing resistance to the cold is of great importance. As a means of developing such resistance, natural environmental factors – water, air, sun – may be used. The UV portion of the spectrum contributes to the production of vitamin D in the skin. This vitamin is necessary for the regulation of calcium-phosphorus metabolism. Its deficiency is one of the causes of rickets. Muscular-articular analyzer. In the muscles, in the connective tissue sheaths dressing them, in the tendons and articular bags there are proprioceptors. Some of them are irritated by muscle contraction, the tension of their connective tissue sheaths, tendons, articular bags, while the other ones – by muscle relaxation and a decrease in the tension of these elements. Impulses transmitted from proprioceptors allow a person to feel the position of his body and its parts without the help of vision, which plays a large role in the orientation of the body in space. In case of disturbance of proprioceptive activities, people are deprived of the opportunity to determine the position of their body without the help of vision. Visceral analyzer. It provides regulation of the internal organs, the relationship and coordination of their activities. A huge role in its functioning belongs to enteroreceptor regulation. The impulses transmitted from enteroreceptors enter the row of brain stem structures and subcortical structures. The highest part of the visceral analyzer is the cerebral cortex; the conductor division is represented mainly by the vagus, the celiac and pelvic nerves. Questions for self-control 1. List the senses and analyzers. Give the definition of the analyzer. What types of receptors exist? Name the main divisions of the visual analyzer. 2. What are the features of the structure of the light-perceiving membrane of the eyeball? 3. What relates to the optical system of the eye? 4. List the parts of the organ of hearing. 5. Which sections does the auditory analyzer include? 6. Tell us about the structural features of the outer, middle and inner ear. 7. What are some methods for determining hearing acuity? 8. What are the functions of the muscular-articular analyzer?

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ADAPTATION TO SCHOOL Adaptation to school is rather a long process, having both physiological and psychological aspects. The first stage is approximate, when children experience a violent reaction and have considerable tension in virtually all body systems. This "physiological storm" lasts a long time (2-3 week). The second stage is an unstable adaptation, when the body searches for and finds some optimal (or close to optimal) variants of reactions to these effects. At the first stage, there is no need to talk about any savings in the body's resources: the body spends everything that it has, and sometimes "takes on debt"; thus, it is so important for the teacher to remember what a high "price" the body of each child pays during this period. At the second stage, this "price" decreases, the "storm" begins to subside. The third stage is a period of relatively stable adaptation, when the body finds the most appropriate (optimal) response options to the load, requiring less stress on all systems. Whatever work a schoolchild does, be it mental work to assimilate new knowledge, the static load that the body experiences during a forced "sitting" posture, or the psychological load of communication in a large and diverse team, the body, or rather each of its systems, should respond to the stress, the work. So, the greater the load for each system, the more resources the body will consume. The possibilities of a child's body are far from endless, and prolonged functional stress and the associated fatigue and overwork can lead to poor health. The duration of all three adaptation phases is approximately 5-6 weeks, this period lasts until approximately the mid of October, and the greatest difficulties arise within 1-4 weeks. 144

The first week is characterized by a rather low level and instability of working capacity, a very high load level of the cardiovascular system, sympathoadrenal system, as well as a low level of coordination (interaction) of various body systems with each other. According to the intensity and amount of the changes occurring in the child's body during the first weeks of training, training sessions can be compared with the effect of extreme loads on an adult, well-trained body. For example, studying the reaction of an organism of first-graders in the classroom in terms of the performance of the cardiovascular system revealed that the load on this system of a child might be compared with the load of the same system of an astronaut in a state of weightlessness. This example convincingly shows how difficult the process of physiological adaptation to school is for a child. Meanwhile, neither the teacher nor the parents often realize the whole complexity of this process, and this ignorance and speeding up the process of learning further complicates the already so difficult period. Inconsistency of the requirements and capabilities of the child leads to adverse changes in the functional state of the central nervous system, to a sharp decrease in learning activity and efficiency. A significant part of schoolchildren shows the signs of pronounced fatigue at the end of studies. At the 5-6th week of training, the performance indicators gradually increase and become more stable, the tension of the main lifesupporting systems of the body (central nervous, cardiovascular, sympathoadrenal) decreases, a relatively stable adaptation to the whole complex of training-related loads occurs. However, for some indicators, this phase (relatively stable adaptation) is delayed and lasts more than 2 months. And, although it is believed that the period of acute physiological adaptation of the organism to the academic load ends at the 5-6th week of training, the entire first year of study (if we compare it with the following periods of training) can be considered a period of unstable and intense regulation of all the systems of the child's body. The success of the adaptation process is largely determined by the state of health of the child. Depending on the state of health, adaptation to school, to the changed conditions of life, can proceed in different ways. There are groups of children with easy adaptation, adaptation of moderate degree and difficult adaptation. With easy adaptation, the intensity of the functional systems of the child's body decreases during the 1st quarter. 145

With the adaptation of moderate degree, various disturbances are observed during the first half of the year. In some children, adaptation to school is difficult. By the end of the 1st quarter, they have mental health problems that manifest in the form of various fears, sleep disorders, appetite disorders, excessive excitability, or, conversely, lethargy, melancholy. There may be complaints of fatigue, headaches, exacerbation of chronic diseases. Significant health problems tend to increasing from the beginning to the end of the school year. The stress of all functional systems of the child's body, associated with the change in the habitual way of life, are most pronounced during the first 2 months of training. Almost all children at the beginning of school year experience motor excitation or lethargy, complain of headaches, poor sleep, and loss of appetite. These negative reactions are more pronounced the sharper the transition from one period of life to another one is, the less prepared is the body of yesterday's preschooler. Of great importance are such factors as the peculiarities of the child's life in the family (how sharply the usual home environment differs from the school environment). Of course, children attending kindergarten, adapt to school much easier compared to the "home" children, unaccustomed to a long stay in the children's team and the regimen of preschool institutions. One of the main criteria characterizing the success of adaptation to systematic education is the child's health status and changes in its indicators under the influence of the academic load. Easy adaptation and, to a certain extent, adaptation of moderate degree, might be considered a logical reaction of the body of children to the changed living conditions. The difficult course of adaptation testifies to the inadequacy of training loads and the training schedule for a first-grader's body. In turn, the difficulty and duration of the adaptation process itself depends on the state of health of the child at the beginning of systematic training. It is easier to tolerate the period of admission to school and better cope with mental and physical exercise for healthy children, with the normal functioning of all body systems and harmonious physical development. The criteria for the successful adaptation of children to school can be an improvement in the dynamics of working capacity during the first months of training, the absence of pronounced adverse changes in health indicators and a good learning of the academic material. Children born in the pathology of pregnancy and childbirth, children who have suffered cranio146

cerebral injuries, those suffering from various chronic diseases and especially those having neuropsychiatric disorders, adapt with greater difficulty. The overall weakness of the child, any disease, both acute and chronic, delayed functional maturation, adversely affecting the state of the central nervous system, cause more problematic adaptation and cause a decrease in working capacity, high fatigue, poor health and reduced success in learning. One of the main tasks that the school sets for the child is the need to master a certain amount of knowledge and skills. Moreover, despite the fact that the general readiness to learn is almost the same for all children, the real readiness for learning is very different. Therefore, a child with an insufficient level of intellecttual development, with a poor memory, with a low development of voluntary attention, will and other qualities necessary for learning will have the greatest difficulties in the adaptation process. The difficulty is that the beginning of learning changes the main type of activity of a preschooler child (a game), but a new type of activity – learning activity – does not appear immediately. Learning at school cannot be identified with learning activities. The start of schooling allows the child to take a new life stance and move on to the implementation of socially significant educational activities. However, at the very beginning of training, first-graders still do not have a need for theoretical knowledge, but this is the need that is the psychological basis for the formation of learning activities. In the early stages of adaptation, the motives associated with cognition, learning, have little weight, and the cognitive motivation to learning and the will are not yet sufficiently developed, they are gradually formed in the process of the learning activity itself. The value of learning for the sake of knowledge, the need to comprehend the new is not for the sake of getting a good grade or avoiding punishment – that should be the basis of the learning activity. As a rule, changes in children's behavior are an indicator of the difficulty of adapting to school. These signs may be excessive excitation and even aggressiveness, and may be, on the contrary, lethargy, depression. There may be (especially in adverse situations) a feeling of fear, unwillingness to go to school. All changes in the child's behavior, as a rule, reflect the peculiarities of psychological adaptation to school. The main indicators of child's adaptation to school are the formation of adequate behavior, the establishment of contacts with 147

other children, the teacher, and the mastery of the skills of learning activities. That is why, when conducting special socio-psychological studies of the adaptation of children to school, the nature of the child's behavior, the characteristics of his contacts with peers and adults, and the development of skills in learning activities are studied. Observations on first-graders have shown that the socio-psychological adaptation of children to school can take place in different ways. The first group of children (56%) adapts to school during the first 2 months of schooling, approximately during the same period when the most acute physiological adaptation occurs. These children relatively quickly join the team, learn at school, make new friends in the classroom; they are usually in a good mood, they are calm, friendly, conscientiously and without apparent tension fulfill all the requirements of the teacher. Sometimes they have difficulties in contacts either with children or with the teacher, since it is still difficult for them to fulfill all the requirements of the rules of behavior. However, by the end of October, these difficulties, as a rule, are leveled, relations are normalized, the child is fully accustomed both to the new status, and to the new requirements, and to the new regime – he becomes a pupil. The second group of children (30%) has a long period of adaptation, the period of non-compliance of their behavior with the requirements of the school is observed. Children cannot accept the situation of learning, communication with the teacher, other children – they can play in the classroom or sort out the relationship with a friend. They do not react to the teacher's remarks or react with tears and resentment. As a rule, these children have trouble in learning. Only by the end of the first half of the year, the reactions of these children become adequate to the requirements of the school, the teacher. The third group (14%) are children, in whom socio-psychological adaptation is associated with considerable difficulties; besides, they do not assimilate the curriculum, they have negative forms of behavior; their negative emotions are sharply manifested. Teachers, classmates, and parents most often complain about these children. It is necessary to pay a special attention to the fact that behind the same external manifestation of negative forms of behavior, or, as it is usually said, bad behavior of a child various reasons can hide. Among these 148

children, there may be those who need special treatment, there may be students with disorders of the neuropsychiatric sphere. Nevertheless, these can be children who are not ready for learning, for example, those who grew up in unfavorable family conditions. Constant failures at school, lack of contact with the teacher lead to alienation and negative attitude of peers. Children become "rejected". However, this gives rise to a protest reaction: they "bully" in turn, shout, behave badly in class, trying to stand out in such a way. If you do not understand the reasons for bad behavior in time, do not correct adaptation difficulties, then altogether it can lead to a breakdown, further mental retardation and adversely affect the child's health, a persistent disturbance of emotional state can turn into a neuro-psychological pathology. Finally, it may simply "overloaded" children who cannot cope with additional load. Anyway, bad behavior is an alarm signal, a reason to take a closer look at the student and, together with his parents, understand the reasons for the difficulties of adapting to school. The success and painlessness of the child's adaptation to school is primarily related to his or her readiness to begin systematic education. The body must be functionally ready (the development of individual organs and systems must reach a required level in order to adequately respond to the effects of the external environment). Otherwise, the adaptation process is delayed, it proceeds with great tension. One – third of the "unprepared" children already at the beginning of the year have a strong load on the cardiovascular system in the process of training, the loss of body mass they often get sick and skip lessons, which means they lag behind their peers even more. It is necessary to dwell specifically on such a factor affecting the success of adaptation, as the age of the start of systematic training. It is not by chance that the duration of the adaptation period for six-yearolds is longer than that for seven-year-olds. Six-year-old children have higher load on all body systems, lower and unstable performance. The year separating a six-year-old child from a seven-year-old is very important for his physical, functional (psycho-physiological) and mental development, therefore many researchers believe that the optimal age for enrollment is not six (until September 1), but 6.5 years. It is during this period (from 6 to 7 years) that many important psychological neoplasms are formed: regulation of behavior, orientation to social norms and requirements intensively develop, the foundations of 149

logical thinking are laid, and an internal plan of action is formed. One should take into account the discrepancy between the biological and passport age, which at this period may be 0.5-1.5 years. The duration and success of the process of adaptation to school, further education is largely determined by the state of children's health. The easiest adaptation to school is in healthy children with health group I, and the most difficult – in children with group III (chronic diseases in a compensated state). There are factors that significantly facilitate the adaptation to school of all children, especially the "unprepared" and weakened ones, the factors that largely depend on the teacher and parents. The most important of them is the rational organization of studies and the rational regime of the day. One of the main conditions, without which it is impossible to preserve the health of children during the school year, is the compliance of the training regime, teaching methods, content and saturation of the curricula, and the environmental conditions with the age-related functional capabilities of first-graders. Ensuring the compliance of two factors – internal morphological and functional and external socio-pedagogical – is a necessary condition for a favorable overcoming this critical period.

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TEST TASKS FOR STUDENTS

1. A) B) C) D)

Mеaning of the term Homeostasis: Contributor and provider Expand The same or constant Receiver

2. A) B) C) D)

What is the normal pH value for body fluids? 7.15-7.25 7.35-7.45 7.55- 7.65 7.00-7.35

3. The junction between one neuron and the next or between a neuron and effectors is called: A) A synapse B) A dendrite C) A neurotransmitter D) A ventricle 4. A) B) C) D)

Sensory neurons have: A short dendrite and a long axon A short dendrite and a short axon A long dendrite and a short axon A long dendrite and a long axon

5. A) B) C) D)

Motor nеurons deliver information From the muscle fiber to the central nervous system Away from the central nervous system to the peripheral nervous system That is classified Away from the central nervous system to a muscle fiber

6. A) B) C) D)

The rеtina does the following: Allows seeing in light and dark, using cones and rods Gives depth perception using binocular vision Contains the ciliary muscles that control the shape of the lens Protects and supports the shape of the eye

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7. A) B) C) D)

Smooth Muscle is Voluntary and Spindle Shaped Voluntary and Striated Involuntary and Spindle Shaped Involuntary and Striated

8. A) B) C) D)

Skeletal Muscle is Voluntary and Spindle Shaped Voluntary and Striated Involuntary and Spindle Shaped Involuntary and Striated

9. A) B) C) D)

Cardiac Muscle is Voluntary and Spindle Shaped Voluntary and Striated Involuntary and Spindle Shaped Involuntary and Striated

10. A) B) C) D)

A hematocrit measures the percentage of: White blood cells Plasma Platelets Red blood cells

11. In a normal blood sample, which of the following cells will be the most abundant? A) Neutrophils B) Basophils C) Eosinophils D) Monocytes 12. This conducts electricity like nerves A) Epicardium B) Pericardium C) Myocardium D) Subvalvular Apparatus 13. This carries the most blood in the body A) Veins B) Capillary Beds C) Veins D) Aorta 14. The following contract together to pump blood A) Right atrium with the right vеntricle and left atrium with the left ventricle B) Right atrium with left atrium and right ventricles with left ventricle

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C) Tricuspid valve and mitral valve D) Aorta and pulmonary artery 15. A) B) C) D) 16. tion is: A) B) C) D)

Nephrons Eliminate wastes from the body Regulate blood volume and prеssure Control levels of electrolytes and metabolites All of the above The function of the loop of the nephron in the process of urine formaReabsorption of water Production of filtrate Reabsorption of solutes Secretion of solutes

17. A) B) C) D)

This is relеased in the duodenum in response to acidic signal Cholecystokinin Gastrin Secretin Peptide

18. A) B) C) D)

This digestive enzyme is produced in the salivary glands and the pancreas Maltase Amylase Pepsin Nuclease

19. This keeps the food bolus in the stomach until it reaches the right consistency to pass into the small intestine A) Esophageal sphincter B) Intrinsic sphincter C) Cardiac sphincter D) Pyloric sphincter 20. A) B) C) D)

This vitamin is required to make red blood cells B1 B2 B6 B12

21. A) B) C) D)

This participates in the synthesis of hemoglobin and melanin Copper Chloride Calcium Iron

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22. A) B) C) D)

All hormones react to a negative feedback except Progesterone Estrogen Prolactin Oxytocin

23. A) B) C) D)

Hormones that are lipids and are synthesized from cholesterol Protiеn Amino acid-derived Polypeptide Steroids

24. A) B) C) D)

Where is the body's "thermostat" found? Within the nеrvous system, in the Hypothalamus Within the integumentary system, in the skin Within the brain, in the corpus callosum Within the Urinary system, in the kidneys

25. with? A) B) C) D) 26. A) B) C) D)

Which body defense mechanism specificity and memory are associated Inflammatory response Phagocytosis by macrophages and neutrophils Interferon T cell and B cеll responses Chief cells produce Epinephrine Glucagon Insulin Parathyroid hormone

27. Fred's blood type is O- and Ginger's is B+. Fred and Ginger have a son who is AB+. What do you conclude? A) If they have a second child, Ginger needs to have an Rh check B) There is no risk to a second child, unless it has a negative blood type C) If the child needs a blood transfusion Fred could provide it safely, but not Ginger D) Fred is not the child's father 28. You take a bloоd sample from a male cyclist at the end of a long race. The hematocrit is 60%. The most likely conclusion is: A) This is within normal range for most adult males B) This cyclist is anemic C) The cyclist is dehydrated D) This low result could indicate liver damage or leukemia

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29. A) B) C) D)

Where is the sіte of maturation for a B cell? Thymus Bone marrow Pancreas Cortex

30. A) B) C) D)

The mеdulla oblongata and pons regulate and measure what? The pH lеvel of your blood Your body temperature The аmount of O2 in your blood The аmount of air in your lungs

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Response to test tasks 1–С

11 – A

21 – A

2–B

12 – С

22 – D

3–A

13 – A

23 – D

4–С

14 – B

24 – A

5–D

15 – D

25 – D

6–A

16 – A

26 – D

7–С

17 – С

27 – D

8–B

18 – B

28 – С

9–D

19 – D

29 – B

10 – D

20 – D

30 – A

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CONTENT

Preface ...................................................................................................... 3 Chapter 1. Patterns of growth and development of the body ................... 5 Chapter 2. Physiology of the musculoskeletal system and age features ......................................................................................... 17 Chapter 3. The internal environment of the body. Composition and properties of blood ........................................................ 27 Chapter 4. Physiology of the cardiovascular system and age features ......................................................................................... 36 Chapter 5. Physiology of respiratory organs and age features ................. 46 Chapter 6. Age-related anatomo-physiological features of the digestion system. Exchange of substances and energy ................... 58 Chapter 7. Physiology of the excretory system and age features ............. 83 Chapter 8. Physiology of the endocrine glands and age features ............. 94 Chapter 9. Development of the nervous system. Higher nervous activity and its formation during the development of a child ........................................................................ 107 Chapter 10. Physiology of sensor systems and age features .................... 133 Chapter 11. Adaptation to school ............................................................ 144 Test tasks of students ................................................................................ 151

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Еducational issue

Tussupbekova Gulmira

PHYSIOLOGY OF DEVELOPMENT OF SCHOOLCHILDREN Educational manual

Editor V. Popova Typesetting U. Moldasheva Cover design Ya. Gorbunov Cover design used photos from sites www.MyTravelBook.org

IB №13580 Signed for publishing 17.04.2020. Format 60x84 1/16. Offset paper. Digital printing. Volume 9,87 printer's sheet. 80 copies. Order №3421. Publishing house «Qazaq University» Al-Farabi Kazakh National University KazNU, 71 Al-Farabi, 050040, Almaty Printed in the printing office of the «Qazaq University» publishing house.

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