Growth hormonal regulation of growth, the importance of external factors. Regulation of growth and development

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on the topic: "The role of hormones in the regulation of mental processes, physical development, linear growth of the body. "

Completed by Khabarov Eduard

The role of hormones in the development of the body

The hormones that make possible and ensure physical, mental and sexual development include growth hormone (GH), which is produced by the anterior pituitary gland, as well as thyroid hormones - thyroxine and triiodothyronine, pancreatic hormone - insulin, sex hormones (Fig. 1 ).

Genetic factors play an important role. Nutrition should be balanced: fasting, diseases accompanied by protein catabolism, lead to stunted growth in children.

Growth is uneven. The first peak in the increase in growth rate occurs in early childhood, the second during puberty. This is due to the simultaneous action of growth hormone, estrogens and androgens. Cessation of growth is associated with the closure of the epiphyseal growth plates under the influence of estrogens and androgens.

The role of growth hormone (STH) in the regulation of growth and physical development

Growth hormone is secreted by the anterior pituitary gland (adenohypophysis). By chemical structure it is a 191 amino acid polypeptide. Growth hormone is species specific.

Figure 1. Regulation by the adenohypophysis of the concentration of STH, TSH, GTG and their functional significance

The synthesis and secretion of STH are carried out under the control of hypothalamic hormones - growth hormone releasing factor (GHF), which stimulates these processes, and somatostatin (SS), which, on the contrary, inhibits the synthesis and release of STH. Hormones of the hypothalamus enter the adenohypophysis with the blood of the portal vessels.

The concentration of the hormone in the blood is higher in children and at a young age (before puberty), less at an older age. The normal concentration of growth hormone in an adult is 2-6 ng / ml, in children - 5-8 ng / ml.

There is a daily (circadian) biological rhythm of hormone secretion - the secretion has a pulsating character, increases at night: the peak of secretion is reached 1-2 hours after falling asleep and decreases during the day.

The secretion of growth hormone is influenced by a large number of factors. They can be conditionally divided into stimulating and inhibitory. The stimulating ones include:

1 Fasting, especially protein fasting, and a decrease in the amount of free fatty acids in the blood, which leads to a significant decrease in the basic substrates needed to replenish the body's energy.

2 An increase in the concentration of certain amino acids in the blood: arginine, leucine, lysine, tryptophan and 5-hydroxytryptophan.

3 Stress factors accompanied by increased physical activity, negative emotions and arousal of the sympathoadrenal system.

4 Biologically active substances: insulin, estrogens, opiates (enkephalins and endorphins), testosterone.

They inhibit secretion: an increase in the concentration of glucose and free fatty acids in the blood; obesity and the aging process; hormones cortisone, progesterone, somatomedin and exogenous growth hormone.

Regulation of GH secretion is carried out by a regulation loop with a negative feedback channel.

When growth hormone enters the bloodstream, it binds to the receptors of the target cell membranes in the liver, where the hormones Somatomedin (insulin-like growth factor - IGF) are produced, which also regulate the secretion of growth hormone through a negative feedback loop mechanism.

Somatomedin (IGF-I), firstly, is carried by the bloodstream into the hypothalamus and stimulates the synthesis of somatostatin, which inhibits the release of STH by the pituitary gland; secondly, Somatomedin is carried directly into the pituitary gland by the blood stream, in which the secretion of growth hormone is also suppressed.

The effect of growth hormone on target cells occurs indirectly through Somatomedin (IGF-I) or directly.

The role of insulin-like growth factor in the body

In the middle of the last century, scientists suggested that there must be an intermediary between the growth hormone known as somatropin and the cells in the body that it affects. After some time, somatomedin was discovered and named insulin-like growth factor.

At first, scientists came to the conclusion that there are three groups of such intermediaries, which were named in the order of numbering: IGF-1 (A), IGF-2 (B), IFZ-3 (C). But after a few years, researchers were able to establish that there is only one group, insulin-like growth factor-1. Despite this, the serial number was assigned to him.

Somatomedin

Insulin-like growth factor is a protein whose structure and function are similar to the hormone insulin. Somatomedin regulates the development and growth of body cells. Scientists believe that it takes an active role in the aging process of the body, if its indicators are closer to the upper mark of the permissible norm (the older the person, the less protein), the life expectancy is longer.

Somatropin, known as growth hormone, which is mediated by IGF-1, is produced in the pituitary gland, an endocrine gland in the brain, with which the hypothalamus controls the entire endocrine system of the body. At the same time, the mediator between somatropin and body cells, somatomedin, is synthesized in the liver under the influence of action on growth hormone receptors. When there is a deficiency of protein in the body, it can begin to be produced in the muscles.

It is from the concentration of somatomedin in the blood that the exact amount of samotropin will be synthesized in the pituitary gland, as well as somatoliberin, which produces the hypothalamus to activate the production of the hormones somatropin and prolactin. This means that when IGF levels are low, the production of hormones from the hypothalamus and pituitary gland increases, and vice versa. But sometimes the interaction between the mediator and somatropin can be disrupted due to insufficient nutrition, poor sensitivity of growth hormone, lack of response at receptors.

Interestingly, although insulin-like growth factor-1 is considered a mediator of somatropin, its amount in the blood also depends on iodine-containing thyroid hormones, androgens, estrogens, progestins, insulin, which increase its synthesis in the liver. But glucocorticoids, steroid hormones that are produced by the adrenal glands, reduce the production of IGF.

This interaction is one of the reasons why hormones of the thyroid, adrenal, pancreas and gonads affect the development and growth of the body. For example, insulin, whose function is to supply glucose and nutrients to every cell in the body, also supplies the liver, providing it with all the amino acids necessary for IGF synthesis.

The interaction of hormones in the body. Mechanism of action

An insulin-like growth factor is synthesized by hepatocytes of the liver, which make up from 60 to 80% of the total mass of the organ, are involved in the production and storage of proteins, the conversion of carbohydrates, the production of cholesterol, bile salts and perform other functions. Having entered the bloodstream from the liver, somatomedin, with the help of carrier proteins, enters tissues and organs, activating bone growth, connective tissue, muscles and having an effect on the body similar to insulin. IGF accelerates the production of proteins and slows down their breakdown, promotes faster fat burning.

Despite the fact that the amount of growth hormone decreases over time (its maximum concentration is observed when the baby has not yet been born: at 4-6 months in the womb), and by the age of fifty its production is reduced to a minimum, IGF affects the development of the body throughout life.

The largest number is observed during adolescence, the smallest in childhood and old age. Scientists note the fact that older people whose protein levels are at the upper limit of the norm live longer and are less prone to cardiovascular diseases. Also, the amount of IGF increases in the mother's body during pregnancy, when the baby's body is actively growing and developing.

Delivery of analyzes

Insulin-like growth factor is not prone to fluctuations during the day, therefore, it is often taken for analysis if necessary to determine the level of somatropin, the concentration of which in the blood is unstable and fluctuates greatly throughout the day. To establish the concentration of IGF, laboratories use immunochemiluminescence analysis (IHLA), which is based on the immune response of antigens (molecules that bind to antibodies).

The method provides for the donation of blood from a vein on an empty stomach, food cannot be taken eight hours before the analysis, it is allowed to drink only non-carbonated mineral water... Half an hour before the procedure, you need to sit in the emergency room so that the blood calms down. If a person has suffered an acute respiratory disease, before passing the tests, you need to completely recover, otherwise you can get inaccurate data.

When filling out the forms, you must indicate the age, since the norm is set for each age category individually: the older the person, the lower the IGF concentration. You do not need to search for decryption of data on your own: the doctor will do it, he will also diagnose.

Reduced IGF

Lack of somatomedin in children delays development and growth, resulting in dwarfism. Protein deficiency in adulthood weakens muscles, decreases bone density, and alters the structure of fats. IGF below normal can be triggered by diseases of the pituitary gland or hypothalamus, which, due to the disease, began to produce a reduced amount of the hormone. This can be the result of hereditary or congenital pathologies, a disorder as a result of trauma, infections, inflammation. It can affect the lowering of insulin-like growth factor problems with the liver (cirrhosis), kidneys, thyroid gland (in hypothyroidism, when the synthesis of iodine-containing hormones decreases). Lack of sleep, unhealthy diet, fasting reduces the synthesis of somatomedin, anorexia is especially bad.

Too high doses of hormonal preparations containing estrogens can lower protein synthesis.

To normalize the level of IGF, you need to find out the reason that reduces its synthesis. For example, if it is hypothyroidism, when treating this ailment, for example, with thyroxine, you can bring it back to normal. In case of improper nutrition, it is necessary to revise the diet, in case of lack of sleep - the daily regimen.

Increased IGF

If the IGF level exceeds the allowable amount, it is also dangerous, since it may indicate the development of a pituitary tumor (mostly benign), which will most likely need to be removed. If after the operation the amount of IGF does not return to normal, this will indicate the inefficiency of the operation.

It is under the influence of a benign tumor of the pituitary gland that the synthesis of growth hormone increases, which can provoke gigantism when a woman's height exceeds 1.9, a man's - 2 meters (not to be confused with hereditary tallness). The first symptoms of gigantism make themselves felt at the age of eight to nine years, when intensive bone growth begins, which leads not only to gigantic growth, but also to the growth of disproportionately long limbs.

When a person stops growing, the disease turns into acromegaly, which causes expansion and thickening of the facial part of the skull, feet, and hands. People who have a similar problem with growth do not live long, since gigantism accompanies a huge number of ailments. To stop growth, medications that block growth hormone synthesis are sometimes used. This does not always help, then doctors decide on a surgical intervention, which may be ineffective.

Research has also shown that increasing IGF concentration can stimulate growth cancer cells and indicate a tumor of the lungs, stomach, chronic renal failure. If you follow a diet that reduces the activity of somatomedin, the risk of developing cancer is reduced. Despite numerous studies in this direction, such data have not yielded special results in the treatment of cancer.

Endocrine system

During intrauterine development, the body is constantly under the influence of hormones, even at a time when they are not yet produced. For example, maternal steroid hormones pass through the placenta to varying degrees and affect the fetus. Some hormones are produced by the placenta.

The hormones produced by the placenta determine the development of adaptive changes in the body of a pregnant woman: proliferation in the mammary glands is stimulated, the endometrium is transformed, the contractile activity of the pregnant uterus is inhibited (chorionic gonadotronin, chorionic lactosomatogronin, progesterone, in late dates pregnancy - estrogens).

Most of the fetus's own hormones begin to be synthesized as early as 2-3 months of intrauterine development, and by the time of birth their concentration in the fetus's blood increases dramatically and significantly exceeds the corresponding level in an adult. After birth, the content of hormones decreases, but this does not deprive the newborn of an important regulatory mechanism, since the milk of a nursing mother contains a large number of components that compensate for the deficiency in hormone production by the child's body and determine its development.

Thus, breast milk, in addition to nutritional, enzymatic and immunological value, also plays the role of a hormone supplier. The concentration of prolactin is especially high in it. In the case of its deficiency (for example, with artificial feeding), distant endocrine disorders occur - hyperprolatinemic hypogonadism, dopamine metabolism is disrupted; more than half of women who received in early childhood artificial feeding suffer from infertility.

The role of hormones in mother's milk is:

o Firstly, in the fact that in conditions of incomplete development of the infant's neuroendocrine mechanisms, they increase his adaptive capabilities in new conditions of existence.

o Secondly, these hormones are necessary for the normal maturation of brain mechanisms. For example, a deficiency of prolactin in breast milk disrupts the development of the dopaminergic system of the child's brain.

In the perinatal and early postnatal periods, there is a high need of the developing brain for anabolic and thyroid hormones, because at this time the synthesis of proteins of the nervous tissue is carried out and the process of its myelination is underway. In addition to the humoral mother-child connection, there is also a reflex communication channel: the act of sucking causes the mother to increase the secretion of prolactin and oxytocin, as a result of which more milk is produced. However, an increase in the synthesis and secretion of hormones (the first mediators) does not yet mean an increase in their influence on the cell membrane of the target organs of the child, because it is also necessary to have sufficient maturation on the membranes of the mechanism that ensures the formation of a second mediator (cAMP), which greatly enhances the effect of the hormone on the tissue.

Hypothalamic-pituitary system

The specific effect of adrenocorticotropic hormone (ACTH) on the adrenal glands begins only at the 7th month of the prenatal period, when the rate of formation of hydrocortisone and testosterone in the adrenal glands increases. In a newborn, all the links of the hypothalamic-pituitary-adrenal system function. Already from the first hours after birth, children react to stressful irritations with an increase in the content of corticosteroids in the blood and urine.

Functions of the sex glands

Between 5 and 7 months of intrauterine development, androgens have a decisive influence on the realization of the genetically programmed sex of the fetus: in the presence of androgens, the hypothalamus differentiates according to male type; in their absence - according to the female type. Androgens contribute to the growth and development of the male reproductive organs.

Thymus gland (thymus)

Hormones produced by the thymus gland (the main one, thymosin) are of great importance both for the differentiation of T cells and for the proliferation and maturation of the cells of the gland itself. It was found that already in a 7.5-week-old embryo, various functions of T-cells are manifested, and by the 12th week of intrauterine development, iron resembles a mature organ and soon becomes the central organ of immunogenesis. T cells act primarily on acid-fasting bacteria, measles viruses, chickenpox and fungi. Helper T cells are required to initiate an antigen response; suppressor T cells play a homeostatic role in keeping the immune response within the required range.

In children, the activity of the gland is fully manifested, since the child has to deal with a huge number of antigens new to him. Before puberty, the increased activity of the thymus is due to the action of thyroxine. Androgenic and estrogenic hormones cause rapid and pronounced atrophy of the thymus gland, and estrogens in this respect are much more active than androgens.

Thyroid

Thyroid hormones increase basal metabolism and body temperature, accelerate myelination of nerve fibers, growth and differentiation of the skeleton; they are necessary to accelerate the metabolism of cholesterol and other lipids (with hypothyroidism, the level of the latter rises).

By the 12th week of intrauterine development, the thyroid gland is already formed, it is able to concentrate iodine and synthesize iodotyrosine. At the same time, the fetal pituitary gland develops, producing thyroid-stimulating hormone (TSH). During childbirth, the release of the latter rises sharply. In newborns, the level of thyroid hormones is maximum, which maintains the intensity of metabolic processes at high level... After 10 years, there are no differences in the activity of the thyroid gland of children and adults.

During puberty, due to pronounced vascularization of the thyroid gland, there is a significant increase in its volume, especially in girls. In this case, a state of hyperthyroidism occurs, accompanied by an increase in energy processes, increased excitability, and an increase in heart rate. During this period, the stimulating effect on the thyroid gland of estrogen and the inhibitory effect of progesterone is especially manifested.

Parathyroid glands

In newborns, a decrease in plasma calcium levels occurs in the first 2 days of life. The parathyroid glands of the fetus show minimal activity before birth. Calcium homeostasis is provided by the hyperfunction of the parathyroid glands of the mother, the release of calcium from the bones of the mother and the enhancement of its reabsorption by the renal tubules. (Growth hormone, thyroxine, calcitonin, cortisol also affect calcium homeostasis). Excess calcium ions are transported across the placenta from the mother to the fetus. When, after birth, the transition of calcium from the mother to the fetus stops, a state of hypocalcemia of the newborn occurs. A decrease in the content of calcium ions in the extracellular fluid leads to a sharp increase in the excitability of the neuromuscular system and tetany, which is sometimes noted in newborns.

Vitamin D also has a significant effect on calcium metabolism in the body of children, which, together with parathyroid hormone, enhances the absorption of calcium from the intestines.

hormone growth endocrine thyroid

Pancreas

In the fetus, insulin-producing B cells appear earlier than glucogen-producing a-cells. During this period of otnogenesis, both hormones are not associated with glucose regulation. In contrast to the adult organism, fetal insulin has a greater effect on increasing the transport of amino acids across cell membranes. The increased concentration of amino acids in the blood causes a rapid increase in insulin secretion. During the first weeks of postnatal life, an insulin response to hyperglycemia develops, although B cells still continue to partially respond to an increase in amino acid concentration.

Children and adolescents usually have a high tolerance to sugar loads. In recent decades, the number of children and adolescents with congenital or acquired insufficiency of the islets of Langerhans has increased significantly, which leads to the development of diabetes mellitus... One of the causes of diabetes is the excessive consumption of sweets by children. Long-term excess sugar consumption depletes B cells and leads to a decrease in insulin production.

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Hormonal growth regulation

The hypothalamus secretes two oppositely acting hormones - releasing factor and somatostatin, which are directed to the adenohypophysis and regulate the production and release of growth hormone. It is still unknown what more stimulates the release of growth hormone from the pituitary gland - an increase in the concentration of releasing factor or a decrease in the content of somatostatin. Growth hormone is secreted not evenly, but sporadically, 3-4 times during the day. Increased secretion of growth hormone occurs under the influence of fasting, severe muscle work, as well as during deep sleep: not without reason, apparently, folk tradition claims that children grow up at night. With age, the secretion of growth hormone decreases, but nevertheless does not stop throughout life. Indeed, in an adult, the growth processes continue, only they no longer lead to an increase in the mass and number of cells, but provide the replacement of outdated, spent cells with new ones.

The growth hormone released by the pituitary gland has two different effects on the cells of the body. The first - direct - action consists in the fact that the breakdown of the previously accumulated reserves of carbohydrates and fats, their mobilization for the needs of energy and plastic metabolism, increases in the cells. The second - indirect - the action is carried out with the participation of the liver. In its cells, under the influence of growth hormone, intermediary substances are produced - somatomedins, which already affect all cells of the body. Under the influence of somatomedins, bone growth, protein synthesis and cell division are enhanced, i.e. the very processes that are usually called "growth" take place. At the same time, molecules of fatty acids and carbohydrates, released due to the direct action of growth hormone, take part in the processes of protein synthesis and cell division.

If the production of growth hormone is reduced, then the child does not grow up and becomes dwarf. However, he maintains a normal physique. Growth can also stop prematurely due to disturbances in the synthesis of somatomedins (it is believed that this substance, for genetic reasons, is not produced in the liver of pygmies, who have the height of a 7-10-year-old child in adulthood). In contrast, hypersecretion of growth hormone in children (for example, due to the development of a benign pituitary tumor) can lead to gigantism. If hypersecretion begins after the ossification of the cartilaginous areas of the bones is already completed under the influence of sex hormones, acromegaly- the limbs, hands and feet, nose, chin and other extremities of the body, as well as the tongue and digestive organs are disproportionately lengthened. Disruption of endocrine regulation in patients with acromegaly often leads to various metabolic diseases, including the development of diabetes mellitus. Timely applied hormonal therapy or surgical intervention allows you to avoid the most dangerous development of the disease.

Growth hormone begins to be synthesized in the human pituitary gland at the 12th week of intrauterine life, and after the 30th week, its concentration in the fetal blood becomes 40 times higher than that of an adult. By the time of birth, the concentration of growth hormone drops by about 10 times, but still remains extremely high. In the period from 2 to 7 years, the content of growth hormone in the blood of children remains approximately at a constant level, which is 2-3 times higher than the level of adults. It is significant that in the same period the most rapid growth processes are completed before the beginning of puberty. Then there comes a period of significant decrease in the level of the hormone - and growth is inhibited. A new increase in the level of growth hormone in boys is noted after 13 years, and its maximum is noted at 15 years, i.e. just at the time of the most intense increase in body size in adolescents. By the age of 20, the content of growth hormone in the blood is set at the level typical for adults.

With the onset of puberty, sex hormones that stimulate protein anabolism are actively involved in the regulation of growth processes. It is under the influence of androgens that the somatic transformation of a boy into a man occurs, since under the influence of this hormone the growth of bone and muscle tissue... An increase in the concentration of androgens during puberty causes an abrupt increase in the linear dimensions of the body - a pubertal growth spurt occurs. However, after this, the same increased content of androgens leads to ossification of growth zones in long bones, as a result of which their further growth stops. In the case of premature puberty, the growth of the body in length may start too early, but it will end early, and as a result, the boy will remain "undersized."

Androgens also stimulate increased growth of muscles and cartilaginous parts of the larynx, as a result of which the voice of boys "breaks", it becomes much lower. The anabolic effect of androgens applies to all skeletal muscle body, due to which the muscles in men are much more developed than in women. Female estrogens have a less pronounced anabolic effect than androgens. For this reason, in girls during puberty, the increase in muscle and body length is less, and the pubertal growth spurt is less pronounced than in boys.

Growth- This is an increase in the total mass in the process of development, leading to a constant increase in the size of the organism.

Growth is provided by the following mechanisms:

1) an increase in cell size;

2) an increase in the number of cells;

3) an increase in non-cellular matter, waste products of cells.

The concept of growth also includes a special shift in metabolism that favors the processes of synthesis, the flow of water and the deposition of intercellular substance.

Growth occurs at the cellular, tissue, organ and organism levels. The increase in mass in the whole organism reflects the growth of its constituent organs, tissues and cells.

There are different types of growth in animals: isometric, allometric, limited and unlimited.

Isometric growth- growth, in which the given organ grows at the same average rate as the rest of the body. In this case, the change in the size of the organism is not accompanied by a change in its external form. The relative sizes of the organ and the organism as a whole remain the same. This type of growth is typical for fish and insects with incomplete transformation (locust, bedbugs).

Allometric growth- growth, in which a given organ grows at a different rate than the rest of the body. In this case, the growth of the organism leads to a change in its proportions. This type of growth is characteristic of mammals and illustrates the relationship between growth and development.

Unlimited growth continues throughout ontogenesis, up to death. Such growth is possessed by fish.

Many other species of vertebrates and invertebrates are characterized by limited growth , i.e. they quickly reach their characteristic size and mass and stop growing.

Growth is carried out due to such cellular processes as an increase in the size of cells and an increase in their number.

There are several types of cell growth:

Auxent- growth by increasing the size of cells. This is a rare type of growth observed in animals with a constant number of cells, such as rotifers, roundworms, and insect larvae. The growth of individual cells is often associated with nuclear polyploidization.

Proliferative growth- growth proceeding by cell multiplication. It is known in two forms: multiplicative and accretionary.

Multiplicative growth characterized by the fact that both cells, arising from the division of the parental cell, again enter into division. The number of cells grows exponentially: if n is the division number, then N = 2. This growth is very efficient and therefore hardly occurs in its pure form or ends very quickly (for example, in the embryonic period).

Accretionary growth lies in the fact that after each subsequent division, only one of the cells is dividing again, then the other stops dividing. In this case, the number of cells grows linearly.

If n is the division number, then N = 2n. This type of growth is associated with the division of the organ into cambial and differentiated zones. Cells move from the first zone to the second, maintaining constant ratios between the sizes of the zones. Such growth is characteristic of organs where the cellular composition is renewed.

The growth rate of an organism in postnatal ontogenesis gradually decreases by the age of four, then remains constant for some time, and at a certain age again makes a leap, called pubertal growth spurt.

This is due to puberty. Puberty growth spurt characterizes only humans and apes. This allows us to evaluate it as a stage in the evolution of primates. It correlates with such a feature of ontogenesis as an increase in the time interval between the end of feeding and puberty. In most mammals, this interval is small and there is no pubertal growth spurt.

Growth regulation is complex and varied. The genetic constitution and environmental factors (oxygen, temperature, light, chemistry, etc.) are of great importance. Almost every species has genetic lines characterized by the limiting sizes of individuals, such as dwarf or, conversely, giant forms. Genetic information is contained in certain genes that determine body length, as well as in other genes that interact with each other. The realization of all information is largely due to the action of hormones. The most important hormone is growth hormone, which is secreted by the pituitary gland from birth to adolescence. Thyroid hormone - thyroxine - plays a very important role throughout the entire growth period. WITH adolescence growth is controlled by steroid hormones of the adrenal glands and gonads. Of the environmental factors, the most important are nutrition, the season, and psychological influences.

The dependence of the ability to grow on the age stage of the organism is interesting. Tissues taken at different stages development and cultivated in a nutrient medium, are characterized by different growth rates. The older the embryo, the slower its tissue grows in culture. Tissue taken from an adult grows very slowly.

The hypothalamus secretes two oppositely acting hormones - releasing factor and somatostatin, which are directed to the adenohypophysis and regulate the production and release of growth hormone. It is still unknown what more stimulates the release of growth hormone from the pituitary gland - an increase in the concentration of releasing factor or a decrease in the content of somatostatin. Growth hormone is secreted not evenly, but sporadically, 3-4 times during the day. An increase in the secretion of growth hormone occurs under the influence of fasting, hard muscle work, and also during deep sleep: it is not for nothing that the folk tradition claims that children grow up at night. With age, the secretion of growth hormone decreases, but nevertheless does not stop throughout life. Indeed, in an adult, the growth processes continue, only they no longer lead to an increase in the mass and number of cells, but provide the replacement of outdated, spent cells with new ones.

If the production of growth hormone is reduced, then the child does not grow up and becomes dwarf. However, he maintains a normal physique. Growth can also stop prematurely due to disturbances in the synthesis of somatomedins (it is believed that this substance, for genetic reasons, is not produced in the liver of pygmies, who have the height of a 7-10-year-old child in adulthood). In contrast, hypersecretion of growth hormone in children (for example, due to the development of a benign pituitary tumor) can lead to gigantism. If hypersecretion begins after the ossification of the cartilaginous areas of the bones is already completed under the influence of sex hormones, acromegaly- the limbs, hands and feet, nose, chin and other extremities of the body, as well as the tongue and digestive organs are disproportionately lengthened. Endocrine dysregulation in patients with acromegaly often leads to various diseases metabolism, including the development of diabetes mellitus. Timely applied hormonal therapy or surgery can avoid the most dangerous development of the disease.

Growth hormone begins to be synthesized in the human pituitary gland at the 12th week of intrauterine life, and after the 30th week its concentration in the fetal blood becomes 40 times higher than that of an adult. By the time of birth, the concentration of growth hormone drops by about 10 times, but still remains extremely high. In the period from 2 to 7 years, the content of growth hormone in the blood of children remains approximately at a constant level, which is 2-3 times higher than the level of adults. It is significant that in the same period the most rapid growth processes are completed before the beginning of puberty. Then there comes a period of significant decrease in the level of the hormone - and growth is inhibited. A new increase in the level of growth hormone in boys is noted after 13 years, and its maximum is observed at 15 years, i.e. just at the time of the most intense increase in body size in adolescents. By the age of 20, the level of growth hormone in the blood is set at a level typical for adults.

With the onset of puberty, sex hormones that stimulate protein anabolism are actively involved in the regulation of growth processes. It is under the influence of androgens that the somatic transformation of a boy into a man occurs, since under the influence of this hormone the growth of bone and muscle tissue is accelerated. An increase in the concentration of androgens during puberty causes an abrupt increase in the linear dimensions of the body - a pubertal growth spurt occurs. However, after this, the same increased content of androgens leads to ossification of the growth zones in the long bones, as a result of which their further growth stops. In the case of premature puberty, the growth of the body in length may start too early, but it will end early, and as a result, the boy will remain "undersized."

Androgens also stimulate increased growth of muscles and cartilaginous parts of the larynx, as a result of which the voice of boys "breaks", it becomes much lower. The anabolic effect of androgens extends to all skeletal muscles of the body, due to which the muscles in men are much more developed than in women. Female estrogens have a less pronounced anabolic effect than androgens. For this reason, in girls during puberty, the increase in muscle and body length is less, and the pubertal growth spurt is less pronounced than in boys.

The growth of the organism. Growth mechanisms, types of growth. Regulation of the growth of the body.

Growth is an increase in total mass during development, leading to a constant increase in the size of the organism.

Growth is provided by the following mechanisms 1) an increase in the size of cells, 2) an increase in the number of cells, 3) an increase in non-cellular matter, products of cell waste. The concept of growth also includes a special shift in metabolism that favors the processes of synthesis, the flow of water and the deposition of intercellular substance. Growth occurs at the cellular, tissue, organ and organism levels.

There are two types of growth - limited and unlimited. Unlimited growth continues throughout ontogenesis, up to death. Such growth is possessed, in particular, by fish. Many other vertebrates are characterized by limited growth, i.e. quickly reach the plateau of their biomass.

Growth characteristics˸

1 – differential b - different growth rates in different parts of the body and at different times.

2 – equifinality- striving to reach the sizes typical for the given species.

3 – allometry- preservation in the process of growth of certain ratios between body weight and skin surface area, musculoskeletal system and muscle mass, etc.

4 - alternation of periods of growth and differentiation

5 - in mammals (and humans) - end of growth by puberty.

Growth regulation is complex and varied. The genetic constitution and environmental factors are of great importance. Almost every species has genetic lines characterized by the limiting sizes of individuals, such as dwarf or, conversely, giant forms. Genetic information is contained in certain genes that determine the length of the body, as well as in other genes that interact with each other. The realization of all information is largely due to the action of hormones. The most important hormone is growth hormone, which is secreted by the pituitary gland from birth to adolescence. The thyroid hormone - thyroxine - plays a very important role throughout the entire growth period. From adolescence, growth is controlled by the steroid hormones of the adrenal glands and gonads. Of the environmental factors, the most important are nutrition, the season, and psychological influences.

Aging and old age. Changes in organs and organ systems during aging. Manifestations of aging at the molecular genetic, cellular, tissue, organ and organism levels.

Old age is a stage of individual development, upon reaching which regular changes in physical condition are observed in the body, appearance, emotional sphere.

Aging is a general biological regularity of the “withering” of an organism, inherent in all living things.

The aging process encompasses all levels of the structural organization of an individual - molecular, subcellular, cellular, tissue, organ.

As a rule, after 40-50 years, a person develops persistent external manifestations of aging, in particular of the skin. Wrinkles appear due to the loss of subcutaneous adipose tissue, age spots, warts. The skin becomes dry and rough due to a decrease in the number of sweat glands, its elasticity is lost, it becomes flabby.

The growth of the organism. Growth mechanisms, types of growth. Regulation of the growth of the body. - concept and types. Classification and features of the category "Growth of an organism. Mechanisms of growth, types of growth. Regulation of growth of an organism." 2015, 2017-2018.