Age-related features of the endocrine system and puberty. Age-related features of the endocrine glands in children

Endocrine glands produce various chemicals called hormones. Hormones act on metabolism in negligible quantities; they serve as catalysts, exerting their effects through the blood and nervous system. Hormones have a huge impact on mental and physical development, growth, changes in the structure of the body and its functions, and determine gender differences.

Hormones are characterized by specificity of action: they have a selective effect only on a specific function (or functions). The influence of hormones on metabolism is carried out mainly through changes in the activity of certain enzymes, and hormones influence either directly their synthesis or the synthesis of other substances involved in a specific enzymatic process. The effect of the hormone depends on the dose and can be inhibited by various compounds (sometimes called antihormones).

It has been established that hormones actively influence the formation of the body already in the early stages of intrauterine development. For example, the thyroid, sex glands and gonadotropic hormones of the pituitary gland function in the fetus. There are age-related features of the functioning and structure of the endocrine glands. Thus, some endocrine glands function especially intensively in childhood, others - in adulthood.

The thyroid gland secretes two hormones - thyroxine And triiodothyronine(T3). Both hormones enhance oxygen absorption and oxidative processes, increase heat generation, and inhibit the formation of glycogen, increasing its breakdown in the liver. The effect of hormones on protein metabolism is associated with age. In adults and children, thyroid hormones have the opposite effect: in adults, with an excess of the hormone, the breakdown of proteins increases and weight loss occurs; in children, protein synthesis increases and the growth and formation of the body accelerates. Both hormones increase the synthesis and breakdown of cholesterol with a predominance of splitting. Artificially increasing the content of thyroid hormones increases basal metabolism and increases the activity of proteolytic enzymes. Stopping their entry into the blood sharply reduces basal metabolism. Thyroid hormones increase immunity.

With hyperfunction of the thyroid gland, signs of Graves' disease appear. With hypofunction of the thyroid gland, a disease such as myxedema is observed.

The parathyroid glands form parathyroid hormone(parathyroidin, parathyroid hormone), which is a protein substance (albumose). The hormone is released continuously and regulates skeletal development and calcium deposition in bones. Parathyroid hormone also maintains at a certain level the content of the enzyme phosphatase, which is involved in the deposition of calcium phosphate in the bones. The secretion of parathyroidin is regulated by the calcium content in the blood: the less it is, the higher the secretion of the gland.

The parathyroid glands also produce another hormone - calcitonin, which reduces the calcium content in the blood, its secretion increases with an increase in the calcium content in the blood.

Chronic hypofunction of the glands is accompanied by increased excitability of the nervous system, weak muscle cramps, digestive disorders, ossification of teeth, and hair loss. With chronic hyperfunction of the glands, the calcium content in the bones decreases, they break down and become brittle; Cardiac activity and digestion are disrupted, the strength of the muscular system decreases, apathy occurs, and in severe cases, death.

Thymus (thymus) gland. The hormone produced by the thymus gland is unknown, but it is believed that it regulates immunity (participates in the process of maturation of lymphocytes), takes part in the process of puberty (inhibits sexual development), enhances growth of the body and retains calcium salts in the bones.

Adrenal glands. About 46 corticosteroids are formed in the cortex (close in chemical structure to sex hormones), of which only 9 are biologically active. In addition, male and female sex hormones are formed in the cortical layer, which are involved in the development of the genital organs in children before puberty.

Based on the nature of their action, corticosteroids are divided into two types.

I. Glucocorticoids enhance the breakdown of carbohydrates, proteins and fats, the conversion of proteins into carbohydrates and phosphorylation, increase the performance of skeletal muscles and reduce their fatigue. With a lack of glucocorticoids, muscle contractions stop (adynamia). Glucocorticoid hormones include: cortisol, corticosterone, cortisone etc. Cortisol and cortisone in all age groups increase oxygen consumption by the heart muscle.

The highest level of glucocorticoid secretion is observed during puberty; after puberty, their secretion stabilizes at a level close to that of adults.

II. Mineralocorticoids. They have little effect on carbohydrate metabolism and mainly affect the exchange of salts and water. These include aldosterone, deoxycorticosterone etc. Mineralocorticoids change the metabolism of carbohydrates, restore the performance of tired muscles by restoring the normal ratio of sodium and potassium ions and normal cellular permeability, increase the reabsorption of water in the kidneys, and increase arterial blood pressure. Mineralocorticoid deficiency reduces sodium reabsorption in the kidneys, which can lead to death. Daily aldosterone secretion increases with age and reaches a maximum by 12–15 years. Deoxycorticosterone enhances body growth, while corticosterone inhibits it.

The hormone tyrosine is continuously synthesized in the adrenal medulla adrenalin and a little norepinephrine. Adrenaline affects the functions of all organs except the secretion of sweat glands. It inhibits the movements of the stomach and intestines, enhances and speeds up the activity of the heart, narrows the blood vessels of the skin, internal organs and non-working skeletal muscles, sharply increases metabolism, increases oxidative processes and heat generation, increases the breakdown of glycogen in the liver and muscles. In small doses, adrenaline stimulates mental activity, in large doses it inhibits it. Adrenaline is destroyed by the enzyme monoamine oxidase.

Pituitary. This is the main gland internally. secretion, affecting the functioning of all endocrine glands and many functions of the body.

1. The most important hormones of the adenohypophysis include:

a) growth hormone ( somatotropic hormone) – accelerates growth while relatively maintaining body proportions. Has species specificity;

b) gonadotropic hormones - accelerate the development of the gonads and increase the formation of sex hormones;

c) lactotropic hormone, or prolactin, stimulates milk secretion;

d) thyroid-stimulating hormone – potentiates the secretion of thyroid hormones;

e) parathyroid-stimulating hormone - causes an increase in the functions of the parathyroid glands and increases the calcium level in the blood;

f) adrenocorticotropic hormone (ACTH) – increases the secretion of glucocorticoids;

g) pancreatic hormone – affects the development and function of the intrasecretory part of the pancreas;

h) hormones of protein, fat and carbohydrate metabolism, etc. – regulate the corresponding types of metabolism.

2. Hormones are formed in the neurohypophysis:

A) vasopressin(antidiuretic) – constricts blood vessels, especially the uterus, increases blood pressure, reduces urination;

b) oxytocin– causes contraction of the uterus and increases the tone of the intestinal muscles, but does not change the lumen of blood vessels and blood pressure levels.

3. In the middle lobe of the pituitary gland only one is formed - melanocyte stimulating hormone, which, under strong lighting, causes movement of the pseudopodia of cells in the black pigment layer of the retina.

The pineal gland has an inhibitory effect on sexual development in immatures and inhibits the functions of the gonads in mature ones. It secretes a hormone that acts on the hypothalamic region and inhibits the formation of gonadotropic hormones in the pituitary gland, which causes inhibition of the internal secretion of the gonads. Gland hormone melatonin unlike intermedin, it reduces pigment cells.

Pancreas. This gland, together with the gonads, belongs to the mixed glands, which are organs of both external and internal secretion. In the pancreas, hormones are produced in the so-called islets of Langerhans. Insulin has the following effects: reduces blood sugar, increasing the synthesis of glycogen from glucose in the liver and muscles; increases cell permeability to glucose and sugar absorption by muscles; retains water in tissues; activates the synthesis of proteins from amino acids and reduces the formation of carbohydrates from protein and fat. Insulin has a stimulating effect on the secretion of gastric juice, rich in pepsin and hydrochloric acid, and enhances gastric motility. Glucagon increases blood sugar levels by increasing the conversion of glycogen to glucose. Decreasing glucagon secretion reduces blood sugar.

A persistent decrease in insulin secretion leads to diabetes mellitus.

Hormone vagotonin increases the activity of the parasympathetic system, and the hormone centropnein stimulates the respiratory center and promotes the transfer of oxygen by hemoglobin.

Sex glands. Like the pancreas, they are classified as mixed glands. Both male and female gonads are paired organs.

Male sex hormones - androgens: testosterone, androstanedione, androsterone, etc. Female sex hormones - estrogens.

Endocrine glands, or endocrine glands, have the characteristic property of producing and secreting hormones. Hormones are active substances whose main action is to regulate metabolism by stimulating or inhibiting certain enzymatic reactions and influencing the permeability of the cell membrane. Hormones are important for growth, development, morphological differentiation of tissues, and especially for maintaining the constancy of the internal environment. For normal growth and development of a child, normal function of the endocrine glands is necessary.

The endocrine glands are located in different parts of the body and have a diverse structure. Endocrine organs in children have morphological and physiological characteristics, which undergo certain changes in the process of growth and development.

The endocrine glands include the pituitary gland, thyroid gland, parathyroid glands, thymus gland, adrenal glands, pancreas, male and female gonads (Fig. 15). Let us dwell on a brief description of the endocrine glands.

The pituitary gland is a small oval-shaped gland located at the base of the skull in the recess of the sella turcica. The pituitary gland consists of the anterior, posterior and intermediate lobes, which have different histological structures, which determines the production of different hormones. By the time of birth, the pituitary gland is quite developed. This gland has a very close connection with the hypothalamic region of the central nervous system through nerve bundles and forms a single functional system with them. Recently, it has been proven that the hormones of the posterior lobe of the pituitary gland and some hormones of the anterior lobe are actually formed in the hypothalamus in the form of neurosecretions, and the pituitary gland is only the site of their deposition. In addition, the activity of the pituitary gland is regulated by circulating hormones produced by the adrenal glands, thyroid and sex glands.

The anterior lobe of the pituitary gland, as currently established, secretes the following hormones: 1) growth hormone, or somatotropic hormone (GH), which acts directly on the development and growth of all organs and tissues of the body; 2) thyroid-stimulating hormone (TSH), which stimulates the function of the thyroid gland; 3) adrenocorticotropic hormone (ACTH), which affects the function of the adrenal glands in the regulation of carbohydrate metabolism; 4) luteotropic hormone (LTH); 5) luteinizing hormone (LH); 6) follicle-stimulating hormone (FSH). It should be noted that LTG, LH and FSH are called gonadotropic; they influence the maturation of the gonads and stimulate the biosynthesis of sex hormones. The middle lobe of the pituitary gland secretes melanoform hormone (MFH), which stimulates the formation of pigment in the skin. The posterior lobe of the pituitary gland secretes the hormones vasopressin and oxytocin, which affect blood pressure levels, sexual development, diuresis, protein and fat metabolism, and uterine contractions.

Hormones produced by the pituitary gland enter the bloodstream, with which they are transported to certain organs. As a result of disruption of the activity of the pituitary gland (increase, decrease, loss of function) for one reason or another, various endocrine diseases can develop (acromegaly, gigantism, Itsenko-Cushing's disease, dwarfism, adiposogenital dystrophy, diabetes insipidus, etc.).

The thyroid gland, consisting of two lobules and an isthmus, is located in front and on both sides of the trachea and larynx. By the time the child is born, this gland is distinguished by its incomplete structure (smaller follicles containing less colloid).

The thyroid gland, under the influence of TSH, secretes triiodothyronine and thyroxine, which contain over 65% iodine. These hormones have a multifaceted effect on metabolism, on the activity of the nervous system, on the circulatory system, influence the processes of growth and development, and the course of infectious and allergic processes. The thyroid gland also synthesizes thyrocalcitonin, which plays a significant role in maintaining normal calcium levels in the blood and determines its deposition in the bones. Consequently, the functions of the thyroid gland are very complex.

Disorders of the thyroid gland can be caused by congenital anomalies or acquired diseases, which is expressed by the clinical picture of hypothyroidism, hyperthyroidism, and endemic goiter.

The parathyroid glands are very small glands, usually located on the posterior surface of the thyroid gland. Most people have four parathyroid glands. The parathyroid glands secrete parathyroid hormone, which has a significant effect on calcium metabolism and regulates the processes of calcification and decalcification in the bones. Diseases of the parathyroid glands can be accompanied by a decrease or increase in hormone secretion (hypoparathyroidism, hyperparathyroidism) (about the goiter, or thymus gland, see “Anatomical and physiological features of the lymphatic system”).

The adrenal glands are paired endocrine glands located in the posterior upper part of the abdominal cavity and adjacent to the upper ends of the kidneys. The mass of the adrenal glands in a newborn is the same as in an adult, but their development is not yet complete. Their structure and function undergo significant changes after birth. In the first years of life, the mass of the adrenal glands decreases and in the prepubertal period reaches the mass of the adrenal glands of an adult (13-14 g).

The adrenal gland consists of a cortex (outer layer) and a medulla (inner layer), which secrete hormones needed by the body. The adrenal cortex produces a large number of steroid hormones, and only some of them are physiologically active. These include: 1) glucocorticoids (corticosterone, hydrocortisone, etc.), which regulate carbohydrate metabolism, promoting the transition of proteins into carbohydrates, have a pronounced anti-inflammatory and desensitizing effect; 2) mineralocorticoids, affecting water-salt metabolism, causing the absorption and retention of sodium in the body; 3) androgens, which have an effect on the body similar to sex hormones. In addition, they have an anabolic effect on protein metabolism, affecting the synthesis of amino acids and polypeptides, increase muscle strength, body weight, accelerate growth, and improve bone structure. The adrenal cortex is under the constant influence of the pituitary gland, which secretes adrenocorticotropic hormone and other adrenopituitary products.

The adrenal medulla produces adrenaline and norepinephrine. Both hormones have the property of increasing blood pressure, constricting blood vessels (with the exception of coronary and pulmonary vessels, which they dilate), and relaxing the smooth muscles of the intestines and bronchi. When the adrenal medulla is damaged, for example due to hemorrhages, the release of adrenaline decreases, the newborn becomes pale, adynamic, and the child dies due to symptoms of motor failure. A similar picture is observed with congenital hypoplasia or absence of the adrenal glands.

The diversity of the function of the adrenal glands also determines the diversity of clinical manifestations of diseases, among which lesions of the adrenal cortex predominate (Addison's disease, congenital adrenogenital syndrome, adrenal tumors, etc.).

The pancreas is located behind the stomach on the posterior abdominal wall, approximately at the level of the II and III lumbar vertebrae. This is a relatively large gland, its weight in newborns is 4-5 g, by the period of puberty it increases 15-20 times. The pancreas has exocrine (secretes the enzymes trypsin, lipase, amylase) and intrasecretory (secretes the hormones insulin and glucagon) functions. Hormones are produced by pancreatic islets, which are cellular clusters scattered throughout the pancreatic parenchyma. Each hormone is produced by special cells and enters directly into the blood. In addition, in the small excretory ducts the glands produce a special substance - lipocaine, which inhibits the accumulation of fat in the liver.

The pancreatic hormone insulin is one of the most important anabolic hormones in the body; it has a strong influence on all metabolic processes and, above all, is a powerful regulator of carbohydrate metabolism. In addition to insulin, the pituitary gland, adrenal glands, and thyroid gland also participate in the regulation of carbohydrate metabolism.

Due to primary damage to the pancreatic islets or a decrease in their function as a result of influence from the nervous system, as well as humoral factors, diabetes mellitus develops, in which insulin deficiency is the main pathogenetic factor.

The sex glands - the testes and ovary - are paired organs. Some newborn boys have one or both testicles located not in the scrotum, but in the inguinal canal or in the abdominal cavity. They usually descend into the scrotum soon after birth. In many boys, the testicles retract inward at the slightest irritation, and this does not require any treatment. The function of the gonads is directly dependent on the secretory activity of the anterior pituitary gland. In early childhood, the gonads play a relatively small role. They begin to function intensively during puberty. The ovaries, in addition to producing eggs, produce sex hormones - estrogens, which ensure the development of the female body, its reproductive apparatus and secondary sexual characteristics.

The testicles produce male sex hormones - testosterone and androsterone. Androgens have a complex and multifaceted effect on the growing child’s body.

During puberty, the growth and development of muscles significantly increases in both sexes.

Sex hormones are the main stimulators of sexual development and are involved in the formation of secondary sexual characteristics (in boys - the growth of a mustache, beard, change in voice, etc., in girls - the development of mammary glands, pubic hair growth, armpits, changes in the shape of the pelvis, etc.). One of the signs of the onset of puberty in girls is menstruation (the result of the periodic maturation of eggs in the ovary), in boys - wet dreams (throwing out fluid containing sperm from the urethra in a dream).

The process of puberty is accompanied by increased excitability of the nervous system, irritability, changes in the psyche, character, behavior, and causes new interests.

During the growth and development of a child, very complex changes occur in the activity of all endocrine glands, therefore the importance and role of the endocrine glands in different periods of life are not the same.

During the first half of extrauterine life, the thymus gland appears to have a great influence on the child’s growth.

In a child, after 5-6 months, the function of the thyroid gland begins to increase, and the hormone of this gland has the greatest effect in the first 5 years, during the period of the most rapid changes in growth and development. The weight and size of the thyroid gland gradually increase with age, especially intensively at the age of 12-15 years. As a result, in the prepubertal and pubertal periods, especially in girls, there is a noticeable enlargement of the thyroid gland, which is usually not accompanied by a violation of its function.

Pituitary growth hormone is less important in the first 5 years of life, only around 6-7 years its influence becomes noticeable. In the prepubertal period, the functional activity of the thyroid gland and the anterior pituitary gland increases again.

During puberty, the secretion of gonadotropic hormones of the pituitary gland, androgens of the adrenal glands and especially hormones of the gonads begins, which affect the functions of the entire organism as a whole.

All endocrine glands are in a complex correlative relationship with each other and in functional interaction with the central nervous system. The mechanisms of these connections are extremely complex and currently cannot be considered fully understood.

Endocrine glands have different embryological origins, as they developed from different primordia. Based on genetic characteristics, they can be divided into five groups. Thus, the thyroid, parathyroid, thymus glands and the endocrine part of the pancreas develop from the endoderm (Fig.); from the mesoderm - the adrenal cortex and the endocrine part of the gonads; from the ectoderm - the pituitary gland, pineal gland, adrenal medulla and paraganglia.

Thyroid gland belongs to the branchiogenic group. It develops from the pharyngeal epithelium of the gill section of the primary intestine, posterior to the tongue rudiment (see Fig.). The blind foramen of the tongue, which is the site of the epithelial rudiment of the thyroid gland, is a remnant of the overgrown thyroglossal duct. The latter exists during embryonic development in the pyramidal process and overgrows during the 4th week of intrauterine life. In newborns, the mass of the gland is about 2 g, it increases with the growth of the whole body, and most intensively during puberty and in an adult reaches 40-60 g. The thyroid gland is located relatively high in a newborn: its isthmus reaches the lower edge of the cricoid cartilage at the top and 5- th tracheal ring below. It takes on the form characteristic of an adult gland only at 5-6 years of age.

Parathyroid glands(branchiogenic group) develop in the form of thickenings from the epithelium of the 3rd and 4th gill pouches. In newborns, they are very close to the thyroid gland, so they are difficult to detect. The greatest activity of these glands is observed in children aged 4-7 years. With age, their size increases and their weight reaches 40-50 mg.

Thymus gland(branchiogenic group) develops from the endoderm of the region of the 3rd gill pouch and is a lymphoepithelial organ (Fig.). It reaches its greatest size in newborns and especially in children aged 2 years; from this time until puberty it increases slightly. Subsequently, the gland involution occurs, connective tissue with many fat cells develops in it; the parenchyma of the gland remains in the form of small islands. In rare cases, iron persists in adults (the so-called status thymicolymphaticus). The weight of the gland in a newborn ranges from 10 to 15 g, and by the end of puberty it reaches 30 g. During puberty, the amount of adipose and connective tissue increases, and the cortex and medulla becomes much smaller.

Pancreas is formed in the form of two rudiments of the endodermal epithelium of the duodenal wall - the dorsal protrusion and the ventral one, which by the end of the 2nd month of intrauterine life fuse into a single organ. In the thickness of the primordia, the epithelium forms cords that turn into tubes, and glandular tissue is formed from the epithelium lining them. Endocrine part of the pancreas pancreatic islets– develop from the endoderm, mainly the dorsal rudiment, and the process of islet formation continues after birth. The cells of the pancreatic islets differentiate earlier than the cells of the exocrine part of the pancreas, despite the fact that they are formed at the same time. The size of the islands reaches 0.1-0.3 mm with age.

Adrenal glands consist of cortex and medulla. The cortex develops from the mesoderm, the medulla appears later and is a derivative of the ectoderm. In a child of the first year of life, the cortex predominates over the brain; in an adult, both are equally developed; in old people, on the contrary, the cortical substance is almost half that of the brain. In a newborn, the weight of both adrenal glands is about 7 g and increases by 6-8 months; the increase in adrenal gland mass continues up to 30 years.

Paraganglia(chromaffin bodies) develop from the ectoderm. In a 16-17 mm embryo, they are presented in the form of two types of cells - sympathoblasts and chromaffinoblasts; the former form sympathetic nodes, the latter participate in the formation of chromaffin organs - paraganglia. They reach their greatest development by 1-1.5 years of age. By the age of 10-13, almost all paraganglia undergo reverse development.

Sex glands– testes and ovaries – are initially formed as indifferent rudiments of the gonads. They are formed from the mesodermal epithelium in the region of the embryonic body cavity on the inner surface of the primary kidney. Subsequently, these glands begin to produce hormones that influence the gradual formation of secondary sexual characteristics.

In the male gonad - testicle– hormones are produced by interstitial cells, the number of which increases significantly in the first half of intrauterine life, and then decreases slightly. During puberty, their number increases again.

In the female reproductive gland - ovary– hormones are produced not only by interstitial cells, but also by the granular layer of maturing follicles. The growth of the latter begins even before the onset of puberty under the influence of gonadotropic hormones produced by the anterior lobe of the pituitary gland.

The anterior lobe of the pituitary gland (neurogenic group) develops from the epithelial protrusion of the dorsal wall of the oral bay in the form of a pocket towards the lower surface of the brain, in the region of the lower wall of the third ventricle, where it joins the future posterior lobe of the pituitary gland. The posterior lobe develops later than the anterior lobe funnel process, processus infundibuli, diencephalon and subsequently joins the anterior lobe. In a newborn, the pituitary gland is often triangular. Its vertical dimension is 4 mm, longitudinal – 7.5 mm, transverse – 8.5 mm; weight 0.125 g; The posterior lobe at the age of 10 years is significantly inferior in size to the anterior lobe. The mass of the adult pituitary gland reaches 0.5-0.6 g.

Pineal gland(neurogenic group) develops from the diencephalon in the area epithalamus, epithalamus, in the form of a small protrusion into which vessels subsequently grow, and a system of tubes surrounded by mesenchymal elements is organized inside. By the age of 7 years, differentiation of the pineal gland ends. In a newborn, the dimensions of the epiphysis are as follows: length 3 mm, width 2.5 mm, thickness 2 mm; birth weight 0.7 g; by the age of 6 years, its mass becomes equal to the mass of the epiphysis of an adult; Iron reaches its maximum development by 14 years of age.

The endocrine system and its role in regulating body functions and behavior in children and adolescents (4 hours)

ENDOCRINE SYSTEM AND ITS AGE FEATURES

1. System of endocrine glands, hormones.

2. Pituitary gland, disorders in children associated with hypo and hypersecretion of growth hormone.

3. The pineal gland and its role in the functioning of the child’s body.

4. Disorders of growth, development, behavior of children and adolescents associated with hypo and hyperfunction of the thyroid gland.

5. The thymus gland is the main organ of immunity in children, its age-related characteristics.

6. Functional features of the adrenal glands and pancreas.

7. Sex glands. The influence of sex hormones on the growth and development of the body of children and adolescents.

Children and adolescents sometimes exhibit abnormalities in growth, development, formation of intelligence, metabolism, immunity, and behavior caused by dysfunction of the endocrine glands. The teacher needs to know the changes that may appear in behavior when endocrine functions are disrupted in order to learn how to assess children’s inadequate emotional reactions and determine measures of individual educational influence. The endocrine system plays a leading role in the physical and mental development of the body of children and adolescents.

Each endocrine gland differs in shape, size, and location, but all glands share some common properties, in particular the ability to secrete hormones into the blood. Blood vessels piercing the gland in all directions perform the function of missing ducts.

All endocrine glands are functionally interconnected. The highest center for the regulation of their functions is the subcutaneous region (hypothalamus), a section of the diencephalon. The hypothalamus is directly connected to the pituitary gland and forms a single unit with it hypothalamic-pituitary system, which controls many body functions.

Endocrine glands play a leading role in the development of the body, the formation of immunity, metabolism, and general health.

Malfunctions of the endocrine system are, first of all, disturbances in the humoral regulation of the body, which can be expressed by an increase (hyperfunction) or a decrease (hypofunction) in the activity of the endocrine glands. Based on their location, the endocrine glands are grouped into four groups:

Pituitary– inferior medullary appendage, the leading endocrine gland, which regulates the activity of a number of other endocrine glands. Produces more than 20 hormones. It is located at the base of the skull (pituitary fossa of the body of the sphenoid bone) and is connected to the brain by a pedicle. The pituitary gland weighs 0.5 - 0.8 g. The gland is divided into an anterior lobe (70% of the total mass), intermediate (10%) and posterior (20%) lobes.

Anterior pituitary gland (adenohypophysis) produces the following hormones:

Growth hormone – STG– growth hormone, or somatotropin (affects protein synthesis in tissues, bone growth, especially tubular bones).

Hormone that stimulates the activity of the adrenal cortex - ACTH (adrenocorticotropic hormone).

Hormone that stimulates the thyroid gland - TSH (thyroid-stimulating hormone).

Hormone that stimulates the development and activity of the gonads, puberty - GTH (gonadotropic hormone). There are two types of GTG: follicle-stimulating And luteinizing hormones.

Follicle stimulating hormone - FSH in women it stimulates the growth of follicles, the secretion of sex hormones, for example, estradiol, hormone secreted by the ovary. In men – spermatogenesis (development and maturation of sperm), synthesis and secretion of sex hormones ( testosterone) .

Luteinizing hormone– LH in women stimulates ovulation, the formation of the corpus luteum of the ovary, and the secretion of sex hormones ( progesterone,- corpus luteum hormone), as well as oogenesis (development and maturation of eggs). In men, the secretion of sex hormones (androgens).

Lactotropic hormone (prolactin) – LTG, stimulating the development of mammary glands, secondary sexual characteristics and lactation.

In adolescence, characterized by rapid endocrine changes, the activity of the anterior lobe of the pituitary gland and the growth hormone secreted by it intensify - growth hormone causes an increase in body length by 7–

10 cm per year. Never, with the exception of the first two years of life, does a person grow so quickly. Activation of growth in children and adolescents occurs under the influence of growth hormone, which stimulates the division of cells of the epiphyseal cartilage and periosteum, increasing the activity of osteoblasts - immature cells of bone tissue.

Possible hypo- and hyperfunction of the anterior pituitary gland.With hypofunction of the anterior pituitary gland Pituitary dwarfism or dwarfism develops, with growth below the level delayed or stopped

130 cm. Pituitary dwarfs are characterized by infantilism (slow development or underdevelopment of the genital area), but their mental development corresponds to their age. Hypofunction of the anterior lobe of the pituitary gland is often caused by damage to it by a tumor, trauma, infection and can lead to pituitary dwarfism. About 8% of children have growth retardation due to hypofunction of the anterior pituitary gland.

With hyperfunction of the anterior pituitary gland in childhood, gigantism develops, characterized by an increase in height above 220 cm . The proportions of the body are preserved, only the head seems small. Giants, like dwarfs, have underdeveloped reproductive systems

With hyperfunction of the anterior lobe in old age, acromegaly. At the same time, the protruding parts of the bones are enlarged - the nose, lower jaw, brow ridges, hands, feet.

The middle lobe of the pituitary gland secretes melanotropic hormone regulating pigment metabolism.

Subtubercular region – hypothalamus controls all processes regulated by the autonomic nervous system: metabolism, body temperature, sleep, wakefulness, motor activity, appetite, hunger, satiety. The hypothalamus and the posterior lobe of the pituitary gland are functionally interconnected via axons. The hypothalamus produces hormones that stimulate the secretion of pituitary hormones. In addition, the hypothalamic hormones enter the posterior lobe of the pituitary gland along the axons, and then the hypothalamic hormones are released into the blood through the posterior lobe of the pituitary gland. For example, biochemists have identified morphine-like hormones of the hypothalamus (liberins, statins), which have narcotic properties, regulating the processes of sexual arousal, emotions, etc. Liberins and statins also regulate the secretion of hormones of the anterior pituitary gland (TSH is regulated by thyreoliberin, STH by somatostatin and somatoliberin, ACTH by corticoliberin, FSH by folliberin, etc.).

The mass of the pituitary gland in a newborn is 0.1 g, at 10 years old – 0.3 g, in a teenager and adult – 0.5 g. Somatotropin is produced from 3–4 months of intrauterine development.

The epiphysis is the superior cerebral appendage located above the quadrigeminal area. midbrain (block 2, Fig. 3). The pineal gland is also called the pineal gland because of its characteristic shape. The weight of the pineal gland is 0.2 g. The gland develops up to 4 years, functions up to 7 years, then atrophies. Pineal gland hormone - melatonin inhibits the formation of gonadotropic hormone in the pituitary gland - GSH, which stimulates the development of the gonads and thereby delays premature puberty.

Thyroid gland located on the anterior surface of the larynx. It consists of two lobes and an isthmus, weighs 30–40 g. Its tissue is formed by follicles, and their wall is a single layer of cells— thyrocytes(block 2, Fig. 4–5), producing iodine-containing hormones - thyroxine, triiodothyronine, thyrocalcitonin, which affect metabolism, the activity of the nervous and cardiovascular systems, growth, and mental development of children and adolescents. During adolescence (12–16 years), the thyroid gland functions intensively.

Hyperthyroidism (excess production of thyroxine) causes increased excitability of the nervous system, pronounced emotionality, rapid fatigue, weakening of the inhibition of nerve centers in the cerebral cortex.

LECTURE 3. NERVOUS REGULATION OF BODY FUNCTIONS IN CHILDREN AND ADOLESCENTS

NERVOUS SYSTEM AND ITS AGE FEATURES. HIGH NERVOUS ACTIVITY AND ITS AGE FEATURES (6 hours)

1. General information about the structure and functions of the brain (briefly).

2. The significance of the works of I.M. Sechenov and I.P. Pavlov for the development of the doctrine of GNI.

3. The concept of excitation and inhibition, stimuli. The importance of knowing the age-related characteristics of the process of excitation and inhibition for the teacher.

4. The concept of the analytical-synthetic activity of the cortex.

5. Reflex, age-related features of reflex activity.

6. Physiological mechanisms of the formation of conditioned reflexes in schoolchildren.

7. Types of cortical inhibition of conditioned reflexes. Conditioned inhibition as the basis for raising children and adolescents.

8. Dynamic stereotype is the physiological basis for the formation of skills, daily routine, and habits in children.

9. Age-related features of the formation of two signaling systems.

10. Types of GNI in children, their physiological classifications, physiological characteristics, significance in the process of training and education.

11. Irradiation and concentration of excitation and inhibition processes. Induction of basic nervous processes. The importance of irradiation and induction in the process of education and training.

12. Teachings of A.A. Ukhtomsky about physiological dominant.

13. Physiological mechanisms of memory.

14. Physiological basis of sleep and prevention of sleep disorders.

Pituitary (hypophysis, s.glandula pituitaria) is located in the pituitary fossa of the sella turcica of the sphenoid bone and is separated from the cranial cavity by a process of the dura mater of the brain, forming the sellar diaphragm. Through an opening in this diaphragm, the pituitary gland is connected to the infundibulum of the hypothalamus of the diencephalon. The transverse size of the pituitary gland is 10-17 mm, anteroposterior - 5-15 mm, vertical - 5-10 mm. The mass of the pituitary gland in men is approximately 0.5 g, in women - 0.6 g. The pituitary gland is covered with a capsule on the outside.

In accordance with the development of the pituitary gland from two different rudiments, two lobes are distinguished in the organ - anterior and posterior. The adenohypophysis, or anterior lobe (adenohypophysis, s.lobus anterior), is larger, making up 70-80% of the total mass of the pituitary gland. It is denser than the posterior lobe. In the anterior lobe, there is a distal part (pars distalis), which occupies the anterior part of the pituitary fossa, an intermediate part (pars intermedia), located on the border with the posterior lobe, and a tuberous part (pars tuberalis), which extends upward and connects with the hypothalamic funnel. Due to the abundance of blood vessels, the anterior lobe has a pale yellow color with a reddish tint. The parenchyma of the anterior lobe of the pituitary gland is represented by several types of glandular cells, between the cords of which sinusoidal blood capillaries are located. Half (50%) of the cells of the adenohypophysis are chromophilic adenocytes, which have fine-grained granules in their cytoplasm that are easily stained with chromium salts. These are acidophilic adenocytes (40% of all cells of the adenohypophysis) and basophilic adenocytes (10%). Basophilic adenocytes include gonadotropic, corticotropic and thyroid-stimulating endocrinocytes. Chromophobic adenocytes are small, they have a large nucleus and a small amount of cytoplasm. These cells are considered the precursors of chromophilic adenocytes. The other 50% of adenohypophysis cells are chromophobe adenocytes.

The neurohypophysis, or posterior lobe (neurohypophysis, s.lobus posterior), consists of the neural lobe (lobus nervosus), which is located in the posterior part of the pituitary fossa, and the funnel (infundibulum), located behind the tubercular part of the adenohypophysis. The posterior lobe of the pituitary gland is formed by neuroglial cells (pituicytes), nerve fibers coming from the neurosecretory nuclei of the hypothalamus to the neurohypophysis, and neurosecretory bodies.

The pituitary gland, through nerve fibers (pathways) and blood vessels, is functionally connected to the hypothalamus of the diencephalon, which regulates the activity of the pituitary gland. The pituitary gland and hypothalamus, together with their neuroendocrine, vascular and nervous connections, are usually considered to be the hypothalamic-pituitary system.

Hormones from the anterior and posterior pituitary glands influence many body functions, primarily through other endocrine glands. In the anterior lobe of the pituitary gland acidophilic adenocytes (alpha cells) produce somotropic hormone (growth hormone), which takes part in the regulation of the processes of growth and development of the young body. Corticotropic endocrinocytes secrete adrenocorticotropic hormone (ACTH), which stimulates the secretion of steroid hormones by the adrenal glands. Thyrotropic endocrinocytes secrete thyrotropic hormone (TSH), which influences the development of the thyroid gland and activates the production of its hormones. Gonadotropic hormones: follicle-stimulating hormone (FSH), luteinizing hormone (LH) and prolactin - affect the body’s puberty, regulate and stimulate the development of follicles in the ovary, ovulation, mammary gland growth and milk production in women, and the process of spermatogenesis in men. These hormones are produced basophilic adenocytes beta cells). Lipotropic factors of the pituitary gland are also secreted here, which influence the mobilization and utilization of fats in the body. In the intermediate part of the anterior lobe, melanocyte-stimulating hormone is formed, which controls the formation of pigments - melanins - in the body.

Neurosecretory cells The supraoptic and paraventricular nuclei in the hypothalamus produce vasopressin and oxytocin. These hormones are transported to the cells of the posterior lobe of the pituitary gland along the axons that make up the hypothalamic-pituitary tract. From the posterior lobe of the pituitary gland, these substances enter the blood. The hormone vasopressin has a vasoconstrictor and antidiuretic effect, for which it also received the name antidiuretic hormone (ADH). Oxytocin has a stimulating effect on the contractility of the uterine muscles, increases the secretion of milk by the lactating mammary gland, inhibits the development and function of the corpus luteum, and affects changes in the tone of the smooth (unstriated) muscles of the gastrointestinal tract.

Development of the pituitary gland

The anterior lobe of the pituitary gland develops from the epithelium of the dorsal wall of the oral bay in the form of a ring-shaped outgrowth (Rathke's pouch). This ectodermal protrusion grows towards the bottom of the future third ventricle. Towards it, from the lower surface of the second cerebral bladder (the future bottom of the third ventricle), a process grows, from which the gray tubercle of the infundibulum and the posterior lobe of the pituitary gland develop.

Vessels and nerves of the pituitary gland

From the internal carotid arteries and the vessels of the arterial circle of the cerebrum, the superior and inferior pituitary arteries are directed to the pituitary gland. The superior pituitary arteries go to the gray nucleus and the infundibulum of the hypothalamus, anastomose here with each other and form capillaries penetrating into the brain tissue - the primary hemocapillary network. The long and short loops of this network form the portal veins, which lead to the anterior lobe of the pituitary gland. In the parenchyma of the anterior pituitary gland, these veins break up into wide sinusoidal capillaries, forming a secondary hemocapillary network. The posterior lobe of the pituitary gland is supplied primarily by the inferior pituitary artery. There are long arterial anastomoses between the superior and inferior pituitary arteries. The outflow of venous blood from the secondary hemocapillary network is carried out through a system of veins flowing into the cavernous and intercavernous sinuses of the dura mater of the brain.

The innervation of the pituitary gland involves sympathetic fibers that penetrate the organ along with the arteries. Postganglionic sympathetic nerve fibers arise from the plexus of the internal carotid artery. In addition, in the posterior lobe of the pituitary gland numerous endings of processes of neurosecretory cells located in the nuclei of the hypothalamus are found.

Age-related features of the pituitary gland

The average weight of the pituitary gland in newborns reaches 0.12 g. The weight of the organ doubles by age 10 and triples by age 15. By the age of 20, the mass of the pituitary gland reaches a maximum (530-560 mg) and remains almost unchanged in subsequent age periods. After 60 years, there is a slight decrease in the mass of this endocrine gland.

Pituitary hormones

The unity of nervous and hormonal regulation in the body is ensured by the close anatomical and functional connection of the pituitary gland and hypothalamus. This complex determines the state and functioning of the entire endocrine system.

The main endocrine gland, which produces a number of peptide hormones that directly regulate the function of peripheral glands, is the pituitary gland. This is a reddish-gray bean-shaped formation, covered with a fibrous capsule weighing 0.5-0.6 g. It varies slightly depending on the gender and age of the person. It remains generally accepted to divide the pituitary gland into two lobes, different in development, structure and functions: the anterior distal - adenohypophysis and the posterior - neurohypophysis. The first makes up about 70% of the total mass of the gland and is conventionally divided into the distal, infundibulal and intermediate parts, the second - into the posterior part, or lobe, and the pituitary stalk. The gland is located in the pituitary fossa of the sella turcica of the sphenoid bone and is connected to the brain through the pedicle. The upper part of the anterior lobe is covered by the optic chiasm and optic tracts. The blood supply to the pituitary gland is very abundant and is carried out by the branches of the internal carotid artery (superior and inferior pituitary arteries), as well as by the branches of the arterial circle of the cerebrum. The superior pituitary arteries participate in the blood supply to the adenohypophysis, and the lower ones - to the neurohypophysis, contacting the neurosecretory endings of the axons of the large cell nuclei of the hypothalamus. The first enter the median eminence of the hypothalamus, where they scatter into a capillary network (primary capillary plexus). These capillaries (with which the axon terminals of small neurosecretory cells of the mediobasal hypothalamus contact) are collected in portal veins, descending along the pituitary stalk into the parenchyma of the adenohypophysis, where they are again divided into a network of sinusoidal capillaries (secondary capillary plexus). Thus, the blood, having previously passed through the median eminence of the hypothalamus, where it is enriched with hypothalamic adenohypophysiotropic hormones (releasing hormones), enters the adenohypophysis.

The outflow of blood, saturated with adenohypophyseal hormones, from the numerous capillaries of the secondary plexus is carried out through a system of veins, which in turn flow into the venous sinuses of the dura mater and then into the general bloodstream. Thus, the portal system of the pituitary gland with the descending direction of blood flow from the hypothalamus is a morphofunctional component of the complex mechanism of neurohumoral control of the tropic functions of the adenohypophysis.

The pituitary gland is innervated by sympathetic fibers traveling along the pituitary arteries. They originate from postganglionic fibers running through the internal carotid plexus associated with the superior cervical ganglia. There is no direct innervation of the adenohypophysis from the hypothalamus. The posterior lobe receives nerve fibers from the neurosecretory nuclei of the hypothalamus.

In terms of histological architecture, the adenohypophysis is a very complex formation. There are two types of glandular cells - chromophobic and chromophilic. The latter, in turn, are divided into acidophilic and basophilic (a detailed histological description of the pituitary gland is given in the corresponding section of the manual). However, it should be noted that the hormones produced by the glandular cells that make up the parenchyma of the adenohypophysis, due to the diversity of the latter, are to some extent different in their chemical nature, and the fine structure of the secreting cells must correspond to the characteristics of the biosynthesis of each of them. But sometimes in the adenohypophysis one can also observe transitional forms of glandular cells that are capable of producing several hormones. There is evidence that the type of glandular cells of the adenohypophysis is not always determined genetically.

Under the diaphragm of the sella turcica is the infundibular part of the anterior lobe. It covers the pituitary stalk, contacting the gray tubercle. This part of the adenohypophysis is characterized by the presence of epithelial cells and an abundant blood supply. It is also hormonally active.

The intermediate (middle) part of the pituitary gland consists of several layers of large secretory-active basophilic cells.

The pituitary gland carries out various functions through its hormones. In its anterior lobe, adrenocorticotropic (ACTH), thyroid-stimulating (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), lipotropic hormones, as well as growth hormone - somatotropic (STO and prolactin) are produced. In the intermediate lobe, melanocyte-stimulating hormone (MSH) is synthesized, and vasopressin and oxytocin accumulate in the posterior.

ACTH

Pituitary hormones represent a group of protein and peptide hormones and glycoproteins. ACTH is the most studied of the anterior pituitary hormones. It is produced by basophilic cells. Its main physiological function is stimulation of biosynthesis and secretion of steroid hormones by the adrenal cortex. ACTH also exhibits melanocyte-stimulating and lipotropic activity. In 1953 it was isolated in its pure form. Subsequently, its chemical structure was established, which in humans and a number of mammals consists of 39 amino acid residues. ACTH is not species specific. Currently, chemical synthesis has been carried out both of the hormone itself and of various fragments of its molecule that are more active than natural hormones. The structure of the hormone contains two sections of the peptide chain, one of which ensures the detection and binding of ACTH to the receptor, and the other provides a biological effect. ACTH appears to bind to the receptor due to the interaction of the electrical charges of the hormone and the receptor. The role of the biological effector of ACTH is performed by a fragment of the molecule 4-10 (Met-Glu-His-Phen-Arg-Tri-Tri).

The melanocyte-stimulating activity of ACTH is due to the presence in the molecule of an N-terminal region consisting of 13 amino acid residues and repeating the structure of alpha-melanocyte-stimulating hormone. This same region contains a heptapeptide, which is present in other pituitary hormones and has some adrenocorticotropic, melanocyte-stimulating and lipotropic activities.

The key point in the action of ACTH should be considered the activation of the protein kinase enzyme in the cytoplasm with the participation of cAMP. Phosphorylated protein kinase activates the enzyme esterase, which converts cholesterol esters into a free substance in fat droplets. The protein synthesized in the cytoplasm as a result of phosphorylation of ribosomes stimulates the binding of free cholesterol to cytochrome P-450 and its transfer from lipid droplets to mitochondria, where all the enzymes that ensure the conversion of cholesterol into corticosteroids are present.

Thyroid-stimulating hormone

TSH - thyrotropin - is the main regulator of the development and functioning of the thyroid gland, the processes of synthesis and secretion of thyroid hormones. This complex protein - a glycoprotein - consists of alpha and beta subunits. The structure of the first subunit coincides with the alpha subunit of luteinizing hormone. Moreover, it is largely the same in different animal species. The sequence of amino acid residues in the human TSH beta subunit has been deciphered and consists of 119 amino acid residues. It may be noted that the beta subunits of TSH in humans and cattle are largely similar. The biological properties and nature of the biological activity of glycoprotein hormones are determined by the beta subunit. It also ensures the interaction of the hormone with receptors in various target organs. However, the beta subunit in most animals exhibits specific activity only after it is combined with the alpha subunit, which acts as a kind of hormone activator. Moreover, the latter is equally likely to induce luteinizing, follicle-stimulating and thyroid-stimulating activities, determined by the properties of the beta subunit. The discovered similarity allows us to conclude that these hormones arose in the process of evolution from one common predecessor; the beta subunit also determines the immunological properties of the hormones. There is an assumption that the alpha subunit protects the beta subunit from the action of proteolytic enzymes, and also facilitates its transport from the pituitary gland to peripheral “target” organs.

Gonadotropic hormones

Gonadotropins are present in the body in the form of LH and FSH. The functional purpose of these hormones generally comes down to ensuring reproductive processes in individuals of both sexes. They, like TSH, are complex proteins - glycoproteins. FSH induces maturation of follicles in the ovaries in females and stimulates spermatogenesis in males. LH causes rupture of the follicle in females with the formation of the corpus luteum and stimulates the secretion of estrogen and progesterone. In males, the same hormone accelerates the development of interstitial tissue and the secretion of androgens. The effects of gonadotropins are dependent on each other and occur synchronously.

The dynamics of gonadotropin secretion in women changes during the menstrual cycle and has been studied in sufficient detail. In the preovulatory (follicular) phase of the cycle, the LH content is at a fairly low level, and FSH is increased. As the follicle matures, the secretion of estradiol increases, which increases the production of gonadotropins by the pituitary gland and the occurrence of both LH and FSH cycles, i.e. sex steroids stimulate the secretion of gonadotropins.

Currently, the structure of LH has been determined. Like TSH, it consists of 2 subunits: a and p. The structure of the LH alpha subunit is largely the same in different animal species; it corresponds to the structure of the TSH alpha subunit.

The structure of the LH beta subunit is noticeably different from the structure of the TSH beta subunit, although it has four identical sections of the peptide chain, consisting of 4-5 amino acid residues. In TSH they are localized at positions 27-31, 51-54, 65-68 and 78-83. Since the beta subunit of LH and TSH determines the specific biological activity of hormones, it can be assumed that homologous regions in the structure of LH and TSH should ensure the connection of beta subunits with the alpha subunit, and structurally different regions should be responsible for the specific biological activity of hormones.

Native LH is very stable to the action of proteolytic enzymes, however, the beta subunit is quickly cleaved by chymotrypsin, and the a subunit is difficult to hydrolyze by the enzyme, i.e., it plays a protective role, preventing access of chymotrypsin to peptide bonds.

As for the chemical structure of FSH, researchers have not yet received definitive results. Just like LH, FSH consists of two subunits, but the FSH beta subunit is different from the LH beta subunit.

Prolactin

Another hormone takes an active part in the processes of reproduction - prolactin (lactogenic hormone). The main physiological properties of prolactin in mammals are manifested in the form of stimulation of the development of mammary glands and lactation, the growth of sebaceous glands and internal organs. It promotes the effect of steroids on secondary sexual characteristics in males, stimulates the secretory activity of the corpus luteum in mice and rats, and is involved in the regulation of fat metabolism. Much attention has been paid to prolactin in recent years as a regulator of maternal behavior; such multifunctionality is explained by its evolutionary development. It is one of the ancient pituitary hormones and is found even in amphibians. Currently, the structure of prolactin in some mammalian species has been completely deciphered. However, until recently, scientists expressed doubts about the existence of such a hormone in humans. Many believed that its function was performed by growth hormone. Convincing evidence has now been obtained for the presence of prolactin in humans and its structure has been partially deciphered. Prolactin receptors actively bind growth hormone and placental lactogen, which indicates a single mechanism of action of the three hormones.

Somatotropin

The growth hormone somatotropin has an even wider spectrum of action than prolactin. Like prolactin, it is produced by acidophilic cells of the adenohypophysis. GH stimulates skeletal growth, activates protein biosynthesis, gives a fat-mobilizing effect, and helps increase body size. In addition, it coordinates metabolic processes.

The participation of the hormone in the latter is confirmed by the fact of a sharp increase in its secretion by the pituitary gland, for example, with a decrease in blood sugar.

The chemical structure of this human hormone has now been completely established - 191 amino acid residues. Its primary structure is similar to the structure of chorionic somatomammotropin or placental lactogen. These data indicate significant evolutionary similarity between the two hormones, although they exhibit differences in biological activity.

It is necessary to emphasize the great species specificity of the hormone in question - for example, GH of animal origin is inactive in humans. This is explained both by the reaction between human and animal GH receptors and by the structure of the hormone itself. Currently, research is underway to identify active centers in the complex structure of GH that exhibit biological activity. Individual fragments of the molecule that exhibit different properties are studied. For example, after hydrolysis of human GH with pepsin, a peptide consisting of 14 amino acid residues and corresponding to the region of the molecule 31-44 was isolated. It did not have a growth effect, but in terms of lipotropic activity it was significantly superior to the native hormone. Human growth hormone, unlike the analogous hormone in animals, has significant lactogenic activity.

The adenohypophysis synthesizes many peptide and protein substances that have a fat-mobilizing effect, and pituitary tropic hormones - ACTH, STH, TSH and others - have a lipotropic effect. In recent years, beta- and γ-lipotropic hormones (LPG) have been highlighted. The biological properties of beta-LPG have been studied in most detail, which, in addition to lipotropic activity, also has melanocyte-stimulating, corticotropin-stimulating and hypocalcemic effects, and also produces an insulin-like effect.

Currently, the primary structure of sheep LPG (90 amino acid residues), lipotropic hormones of pigs and cattle has been deciphered. This hormone is species specific, although the structure of the central region of beta-LPH is the same in different species. It determines the biological properties of the hormone. One of the fragments of this region is found in the structure of alpha-MSH, beta-MSH, ACTH and beta-LPG. It has been suggested that these hormones evolved from the same precursor. γ-LPG has weaker lipotropic activity than beta-LPG.

Melanocyte-stimulating hormone

This hormone, synthesized in the intermediate lobe of the pituitary gland, in its biological function stimulates the biosynthesis of the skin pigment melanin, promotes an increase in the size and number of melanocyte pigment cells in the skin of amphibians. These qualities of MSH are used in biological testing of the hormone. There are two types of hormone: alpha and beta MSH. It has been shown that alpha-MSH is not species specific and has the same chemical structure in all mammals. Its molecule is a peptide chain consisting of 13 amino acid residues. Beta-MSH, on the contrary, is species specific, and its structure varies in different animals. In most mammals, the beta-MSH molecule consists of 18 amino acid residues, and only in humans it is extended from the amino end by four amino acid residues. It should be noted that alpha-MSH has some adrenocorticotropic activity, and its effect on animal and human behavior has now been proven.

Oxytocin and vasopressin

Vasopressin and oxytocin accumulate in the posterior lobe of the pituitary gland, which are synthesized in the hypothalamus: vasopressin - in the neurons of the supraoptic nucleus, and oxytocin - in the paraventricular nucleus. They are then transferred to the pituitary gland. It should be emphasized that the precursor of the hormone vasopressin is first synthesized in the hypothalamus. At the same time, neurophysin protein types 1 and 2 are produced there. The first binds oxytocin, and the second binds vasopressin. These complexes migrate in the form of neurosecretory granules in the cytoplasm along the axon and reach the posterior lobe of the pituitary gland, where the nerve fibers end in the wall of the vessels and the contents of the granules enter the blood. Vasopressin and oxytocin are the first pituitary hormones with a fully established amino acid sequence. In their chemical structure, they are nonapeptides with one disulfide bridge.

The hormones in question produce a variety of biological effects: they stimulate the transport of water and salts through membranes, have a vasopressor effect, increase contractions of the smooth muscles of the uterus during childbirth, and increase the secretion of the mammary glands. It should be noted that vasopressin has a higher antidiuretic activity than oxytocin, while the latter has a stronger effect on the uterus and mammary gland. The main regulator of vasopressin secretion is water consumption; in the renal tubules it binds to receptors in the cytoplasmic membranes, followed by activation of the enzyme adenylate cyclase in them. Different parts of the molecule are responsible for the binding of the hormone to the receptor and for the biological effect.

The pituitary gland, connected through the hypothalamus with the entire nervous system, combines into a functional whole the endocrine system, which is involved in ensuring the constancy of the internal environment of the body (homeostasis). Within the endocrine system, homeostatic regulation is carried out on the basis of the principle of feedback between the anterior lobe of the pituitary gland and the “target” glands (thyroid gland, adrenal cortex, gonads). An excess of the hormone produced by the “target” gland inhibits, and its deficiency stimulates the secretion and release of the corresponding tropic hormone. The hypothalamus is included in the feedback system. It is in it that the receptor zones sensitive to hormones of the “target” glands are located. By specifically binding to hormones circulating in the blood and changing the response depending on the concentration of hormones, the hypothalamic receptors transmit their effect to the corresponding hypothalamic centers, which coordinate the work of the adenohypophysis, releasing hypothalamic adenohypophysiotropic hormones. Thus, the hypothalamus should be considered as a neuro-endocrine brain.

Literature used

1. Lectures on human anatomy and physiology with the basics of pathology – Baryshnikov S.D. 2002
2. Atlas of Human Anatomy – Bilich G.L. – Volume 1. 2014
3. Anatomy according to Pirogov – V. Shilkin, V. Filimonov – Atlas of human anatomy. 2013
4. Atlas of Human Anatomy – P.Tank, Th. Gest – Lippincott Williams & Wilkins 2008
5. Atlas of Human Anatomy – Team of authors – Diagrams – Drawings – Photographs 2008
6. Fundamentals of medical physiology (second edition) – Alipov N.H. 2013