Age-related features of the pineal gland. Have a remote action
Pituitary
The pituitary gland is of ectodermal origin. The anterior and middle (intermediate) lobes are formed from the epithelium of the oral cavity, the neurohypophysis (posterior lobe) - from the diencephalon. In children, the anterior and middle lobes are separated by a gap; over time, it closes and both lobes are closely adjacent to each other.
The endocrine cells of the anterior lobe differentiate in the embryonic period, and at 7-9 weeks they are already capable of synthesizing hormones.
The mass of the pituitary gland in newborns is 100-150 mg, and the size is 2.5-3 mm. In the second year of life, it begins to increase, especially at the age of 4-5 years. After this, until the age of 11, the growth of the pituitary gland slows down, and from the age of 11 it accelerates again. By the period of puberty, the mass of the pituitary gland averages 200-350 mg, by 18-20 years old - 500-600 mg. The diameter of the pituitary gland reaches 10-15 mm by adulthood.
Pituitary hormones: functions and age-related changes
The anterior lobe of the pituitary gland synthesizes hormones that control the function of peripheral endocrine glands: thyroid-stimulating, gonadotropic, adrenocorticotropic, as well as somatotropic hormone (growth hormone) and prolactin. Functional activity adenohypophysis is completely regulated by neurohormones, it does not receive nervous influences CNS.
Somatotropic hormone (somatotropin, growth hormone) - growth hormone determines growth processes in the body. Its formation is regulated by the hypothalamic GH-releasing factor. This process is also influenced by the hormones of the pancreas and thyroid glands, and the hormones of the adrenal glands. Factors that increase the secretion of GH include hypoglycemia (lowering blood glucose levels), fasting, certain types of stress, intense physical labor. The hormone is also released during deep sleep. In addition, the pituitary gland occasionally secretes large amounts of GH in the absence of stimulation. The biological effect of GH is mediated by somatomedin, which is produced in the liver. STH receptors (i.e. structures with which the hormone directly interacts) are built into cell membranes. The main role of growth hormone is stimulation of somatic growth. Its activity is associated with growth skeletal system, increase in the size and weight of organs and tissues, protein, carbohydrate and fat metabolism. GH acts on many endocrine glands, kidneys, and on the functions immune system. As a growth stimulator at the tissue level, growth hormone accelerates the growth and division of cartilage cells, the formation of bone tissue, promotes the formation of new capillaries, and stimulates the growth of epiphyseal cartilage. Subsequent replacement of cartilage with bone tissue is ensured by thyroid hormones. Both processes are accelerated under the influence of androgens; growth hormone stimulates the synthesis of RNA and proteins, as well as cell division. There are gender differences in the content of growth hormone and indices of muscle development, skeletal system and fat deposition. Excessive amount of growth hormone disrupts the water exchange, reducing glucose use peripheral tissues, and contributes to the development of diabetes. Like others pituitary hormones, HGH promotes the rapid mobilization of fat from the depot and the entry of energy material into the blood. In addition, retention of extracellular water, potassium and sodium may occur, and calcium metabolism may also be impaired. Excess of the hormone leads to gigantism (Fig. 3.20). At the same time, the growth of skeletal bones accelerates, but the increase in the secretion of sex hormones upon reaching puberty stops it. Increased secretion of growth hormone is also possible in adults. In this case, growth of the extremities of the body (ears, nose, chin, teeth, fingers, etc.) is observed. Bone growths may form, and the size of the digestive organ (tongue, stomach, intestines) may increase. This pathology is called acromegaly and is often accompanied by the development of diabetes.
Children with insufficient secretion of growth hormone develop into dwarfs of a “normal” physique (Fig. 3.21). Growth retardation appears after 2 years, but intellectual development however, it is usually not violated.
The hormone is determined in the pituitary gland of a 9-week fetus. Subsequently, the amount of growth hormone in the pituitary gland increases and by the end of the intrauterine period increases 12,000 times. GH appears in the blood at 12 weeks intrauterine development, and in 5-8 month old fetuses it is approximately 100 times more than in adults. The concentration of GH in the blood of children continues to remain high, although during the first week after birth it decreases by more than 50%. By 3-5 years of age, the level of growth hormone is the same as in adults. In newborns, growth hormone is involved in the immunological defense of the body, influencing lymphocytes.
HGH ensures the normal physical development of the child. Under physiological conditions, hormone secretion is episodic. In children, GH is secreted 3-4 times during the day. The total amount released during deep night sleep is significantly greater than in adults. In connection with this fact, the need for adequate sleep for the normal development of children becomes obvious. With age, the secretion of GH decreases.
The growth rate in the prenatal period is several times higher than in the postnatal period, but the endocrine glands do not influence this process of decisive importance. It is believed that fetal growth is mainly influenced by placental hormones, factors of the maternal body and depends on the genetic development program. The cessation of growth occurs probably because the general hormonal situation changes in connection with the achievement of puberty: estrogens reduce the activity of growth hormone.
Thyroid-stimulating hormone (TSH) regulates the activity of the thyroid gland according to the body's needs. The mechanism of the effect of TSH on the thyroid gland is still not fully understood, but its administration increases the mass of the organ and increases the secretion of thyroid hormones. The effect of TSH on protein, fat, carbohydrate, mineral and water metabolism is carried out through thyroid hormones.
TSH-producing cells appear in 8-week embryos. During the entire intrauterine period, the absolute content of TSH in the pituitary gland increases and in a 4-month fetus it is 3-5 times higher than in adults. This level persists until birth. TSH begins to affect the fetal thyroid gland in the second third of pregnancy. however, the dependence of thyroid function on TSH in the fetus is less pronounced than in adults. The connection between the hypothalamus and the pituitary gland is established only in the last months of intrauterine development.
In the first year of a child's life, the concentration of TSH in the pituitary gland increases. A significant increase in synthesis and secretion is observed twice: immediately after birth and in the period preceding puberty (prepuberty). The first increase in TSH secretion is associated with the adaptation of newborns to living conditions, the second corresponds to hormonal changes, including increased function of the gonads. The maximum secretion of the hormone is achieved between the ages of 21 and 30 years; at 51-85 years, its value is halved.
Adrenocorticotropic hormone (ACTH) acts indirectly on the body by stimulating the secretion of adrenal hormones. In addition, ACTH has direct melanocyte-stimulating and lipolytic activity, so an increase or decrease in ACTH secretion in children is accompanied by complex dysfunctions of many organs and systems.
With increased secretion of ACTH (Cushing's disease), growth retardation, obesity (fat deposition mainly on the trunk), moon-shaped face, premature development pubic hair, osteoporosis, hypertension, diabetes, trophic skin disorders (stretch marks). With insufficient secretion of ACTH, changes characteristic of a lack of glucocorticoids are detected.
In the prenatal period, the secretion of ACTH in the embryo begins from the 9th week, and at the 7th month its content in the pituitary gland reaches high level. During this period, the fetal adrenal glands respond to ACTH - the rate of formation of hodrocortisone and testosterone increases in them. In the second half of intrauterine development, not only direct, but also feedback connections between the pituitary gland and the adrenal glands of the fetus begin to operate. In newborns, all parts of the hypothalamus-pituitary-adrenal cortex system function. From the first hours after birth, children already react to stressful stimuli (associated, for example, With protracted labor, surgical interventions etc.) an increase in the content of corticosteroids in the urine. These reactions, however, are less pronounced than in adults, due to the low sensitivity of the hypotadamic structures to changes in the internal and external environment of the body. The influence of the hypothalamic nuclei on the function of the adenohypophysis increases. which, under stress conditions, is accompanied by an increase in ACTH secretion. In old age, the sensitivity of the hypothalamic nuclei decreases again, which is associated with a less pronounced adaptation syndrome in old age.
Gonadotropins (gonadotropins) are called follicle-stimulating and luteinizing hormones
Follicle-stimulating hormone (FSH) in the female body causes the growth of ovarian follicles and promotes the formation of estrogens in them. In the male body, it affects spermatogenesis in the testes. FSH release depends on stage and age
Luteinizing hormone (LH) causes ovulation, promotes the formation corpus luteum in the ovaries female body, and in the male body stimulates the growth of seminal vesicles and prostate gland, as well as the production of androgens in the testes.
Cells that produce FSH and LH develop in the pituitary gland by the 8th week of intrauterine development, at which time LH appears in them. and at the 10th week - FSH. Gonadotropins appear in the blood of the fetus from 3 months of age. In the blood of female fetuses, especially in the last third of intrauterine development, their concentration is higher than in males. The maximum concentration of both hormones occurs in the period of 4.5-6.5 months prenatal period The significance of this fact is still not fully understood
Gonadotropic hormones stimulate endocrine secretion gonads of the fetus, but do not control their sexual differentiation. In the second half of the intrauterine period, a connection is formed between the hypothalamus, the gonadotropic function of the pituitary gland and the hormones of the gonads. This occurs after fetal sex differentiation under the influence of testosterone.
In newborns, the concentration of LH in the blood is very high, but during the first week after birth it decreases and remains low until 7-8 years of age. During puberty, the secretion of gonadotropins increases, by the age of 14 it increases 2-2.5 times. In girls, gonadotropic hormones cause the growth and development of the ovaries, cyclical secretion of FSH and LH appears, which causes the onset of new sexual cycles. By the age of 18, FSH and LH levels reach adult values.
Prolactin, or luteotropic hormone (LTP. stimulates the function of the corpus luteum and promotes lactation, i.e. the formation and secretion of milk. The formation of the hormone is regulated by the prolactin-inhibiting factor of the hypothalamus, estrogens and thyrotropin-releasing hormone (TRH) of the hypothalamus. The last two hormones have a stimulating effect on the secretion of the hormone. An increase in the concentration of prolactin leads to an increase in the release of dopamine by the cells of the hypothalamus, which inhibits the secretion of the hormone. This mechanism works during the absence of lactation; excess dopamine inhibits the activity of the cells that form prolactin.
The secretion of prolactin begins from the 4th month of intrauterine development and increases significantly in the last months of pregnancy. It is believed that it is also involved in the regulation of metabolism in the fetus. At the end of pregnancy, prolactin levels become high in both the mother's blood and amniotic fluid. In newborns, the concentration of prolactin in the blood is high. It decreases during the first year of life. and increases during puberty. and it is stronger in girls than in boys. In teenage boys, prolactin stimulates the growth of the prostate gland and seminal vesicles.
The middle lobe of the pituitary gland influences the processes of hormone formation in the adenohypophysis. It is involved in the secretion of melanostimulating hormone (MSH) (melanotropin) and ACTH. MSH is important for skin and hair pigmentation. In the blood of pregnant women, its content is increased, and therefore pigment spots appear on the skin. In fetuses, the hormone begins to be synthesized at 10-11 weeks. but its function in development is still not completely clear.
The posterior lobe of the pituitary gland, together with the hypothalamus, functionally forms a single whole. Hormones synthesized in the nuclei of the hypothalamus - vasopressin and oxytocin - are transported to the posterior lobe of the pituitary gland and are stored here until released into the blood
Vasopressin, or antidiuretic hormone (ADH). The target organ of ADH is the kidneys. The epithelium of the renal collecting ducts becomes permeable to water only under the influence of ADH. which ensures passive reabsorption of water. Under conditions of increased salt concentration in the blood, the concentration of ADH increases and, as a result, urine becomes more concentrated and water loss is minimal. When the concentration of salts in the blood decreases, the secretion of ADH decreases. Alcohol consumption further reduces the secretion of ADH, which explains the significant diuresis after drinking fluids with alcohol.
When inserted large quantities ADH in the blood clearly manifests a narrowing of the arteries due to the stimulation of vascular smooth muscles by this hormone, resulting in increased blood pressure(vasopressor effect of the hormone). A sharp drop in blood pressure due to blood loss or shock sharply increases the secretion of ADH. As a result, blood pressure increases. A disease that occurs when the secretion of ADH is impaired. called diabetes insipidus. This creates a large number of urine with normal sugar content
The antidiuretic hormone of the pituitary gland begins to be released in the 4th month of embryonic development, the maximum of its release occurs at the end of the first year of life, then the antidiuretic activity of the neurohypophysis begins to fall to fairly low values, and at the age of 55 years it is approximately 2 times less than in a one-year-old child .
The target organ for oxytocin is muscle layer uterus and myoepithelial cells of the mammary gland. Under physiological conditions, the mammary glands begin to secrete milk on the first day after birth, and at this time the baby can already suck. The act of sucking serves as a strong stimulus for the nipple's tactile receptors. From these receptors, impulses are transmitted along nerve pathways to the neurons of the hypothalamus, which are also secretory cells that produce oxytocin. The latter is transported in the blood to myoepithelial cells. lining the mammary gland. Myoepithelial cells are located around the alveoli of the gland, and during contraction, milk is squeezed into the ducts. Thus, to extract milk from the gland, the baby does not require active sucking, since the “milk ejection” reflex helps him.
Activation of labor is also associated with oxytocin. With mechanical irritation of the birth canal nerve impulses, which enter the neurosecretory cells of the hypothalamus, causing the release of oxytocin into the blood. Towards the end of pregnancy, under the influence of the female sex hormones estrogen, the sensitivity of the muscles of the uterus (myometrium) to oxytocin sharply increases. At the beginning of labor, the secretion of oxytocin increases, which causes weak contractions of the uterus, pushing the fetus towards the cervix and vagina. Stretching of these tissues causes the excitation of numerous mechanoreceptors in them. From which the signal is transmitted to the hypothalamus. Neurosecretory marks of the hypothalamus respond by releasing new portions of oxytocin, due to which uterine contractions intensify. This process eventually progresses to labor, during which the fetus and placenta are expelled. After expulsion of the fetus, irritation of mechanoreceptors and the release of oxytocin stop.
The synthesis of hormones of the posterior lobe of the pituitary gland begins in the nuclei of the hypothalamus in the 3rd-4th month of the intrauterine period, and in the 4th-5th month they are found in the pituitary gland. The content of these hormones in the pituitary gland and their concentration in the blood gradually increase by the time the child is born. In children in the first months of life, the antidiuretic effect of vasopressin does not play a significant role; only with age does its importance in retaining water in the body increase. In children, only the antidiuretic effect of oxytocin is manifested; its other functions are weakly expressed. The uterus and mammary glands begin to respond to oxytocin only after the completion of puberty, that is, after prolonged action on the uterus of the sex hormones estrogen and progesterone, and on the mammary gland - the pituitary hormone prolactin.
Endocrine system of the human body It is represented by endocrine glands that produce certain compounds (hormones) and release them directly (without ducts leading out) into the blood. In this, endocrine glands differ from other (exocrine) glands; the product of their activity is released only into the external environment through special ducts or without them. Exocrine glands are, for example, salivary, gastric, sweat glands etc. In the body there are also mixed glands, which are both exocrine and endocrine. Mixed glands include the pancreas and gonads.
Hormones of the endocrine glands are carried through the bloodstream throughout the body and perform important regulatory functions: they influence, regulate cellular activity, growth and development of the body, cause changes in age periods, affect the functioning of the respiratory, circulatory, digestive, excretory and reproduction organs. Under the influence and control of hormones (in optimal external conditions) the entire genetic program of human life is also implemented.
The glands are located in different places of the body according to their topography: in the head area there are the pituitary gland and epiphysis, in the neck and chest The thyroid, a pair of thyroid and thymus (thymus) glands are located. In the abdomen are the adrenal glands and pancreas, in the pelvic area are the gonads. In different parts of the body, mainly along large blood vessels, there are small analogues of endocrine glands - paraganglia.
Features of the endocrine glands at different ages
The functions and structure of the endocrine glands change significantly with age.
The pituitary gland is considered the gland of all glands since its hormones affect the work of many of them. This gland is located at the base of the brain in the recess of the sella turcica of the sphenoid (main) bone of the skull. In a newborn, the mass of the pituitary gland is 0.1-0.2 g, at 10 years it reaches a mass of 0.3 g, and in adults - 0.7-0.9 g. During pregnancy in women, the mass of the pituitary gland can reach 1.65 g . The gland is conventionally divided into three parts: anterior (adenohypophysis), posterior (non-gyrogypophysis) and intermediate. In the area of the adenohypophysis and the intermediate portion of the pituitary gland, most of the gland's hormones are synthesized, namely somatotropic hormone (growth hormone), as well as adrenocorticotropic (ACTA), thyroid-stimulating (THG), gonadotropic (GTG), luteotropic (LTG) hormones and prolactin. In the area of the neurohypophysis they acquire active form hypothalamic hormones: oxytocin, vasopressin, melanotropin and Mizin factor.
The pituitary gland is closely connected by neural structures with the hypothalamus of the diencephalon, due to which the interaction and coordination of the nervous and endocrine regulatory systems is carried out. Hypothalamic-pituitary neural pathway (the cord connecting the pituitary gland to the hypothalamus) has up to 100 thousand nerve processes of hypothalamic neurons, which are capable of creating a neurosecretion (transmitter) of an excitatory or inhibitory nature. The processes of hypothalamic neurons have terminal endings (synapses) on the surface blood capillaries posterior lobe of the pituitary gland (neurohypophysis). Once in the blood, the mediator is further transported to the anterior lobe of the pituitary gland (adenohypophysis). The blood vessels at the level of the adenohypophysis again divide into capillaries, flow around the islets of secretory cells and, thus, through the blood, influence the activity of hormone formation (accelerate or slow down). According to the scheme that is described, the relationship in the work of the nervous and endocrine regulatory systems is precisely realized. In addition to communication with the hypothalamus, the pituitary gland receives neuronal processes from the gray tubercle of the anterior part cerebral hemispheres, from the cells of the thalamus, which is at the bottom of the 111th ventricle of the brainstem and from solar plexus autonomic nervous system, which are also capable of influencing the activity of the formation of pituitary hormones.
The main hormone of the pituitary gland is somatotropic, which regulates bone growth, increase in body length and weight. At insufficient quantities growth hormone (hypofunction of the gland), dwarfism is observed (body length up to 90-100 ohms, low body weight, although mental development can proceed normally). Excess of somatotropic hormones in childhood(hyperfunction of the gland) leads to pituitary gigantism (body length can reach 2.5 meters or more, mental development often suffers). The pituitary gland produces, as mentioned above, adrenocorticotropic hormone (ACTH), gonadotropic hormones (GTH), and thyroid-stimulating hormone (TSH). A greater or lesser amount of the above hormones (regulated by the nervous system), through the blood, affects the activity of the adrenal glands, gonads and thyroid glands, respectively, changing, in turn, their hormonal activity, and through this influencing the activity of those processes. which are regulated. The pituitary gland also produces the melanophore hormone, which affects the color of the skin, hair and other structures of the body, vasopressin, which regulates blood pressure and water metabolism, and oxytocin, which affects the processes of milk secretion, the tone of the walls of the uterus, etc.
Pituitary hormones. During puberty, gonadotropic hormones of the pituitary gland are especially active, influencing the development of the gonads. The appearance of sex hormones in the blood, in turn, inhibits the activity of the pituitary gland ( Feedback). The function of the pituitary gland stabilizes in the post-pubertal period (at 16 - 18 years). If the activity of somatotropic hormones persists even after the completion of the body’s growth (after 20–24 years), then acromegaly develops, when individual parts of the body in which the ossification processes have not yet completed become disproportionately large (for example, the hands, feet, head, ears become significantly enlarged and other body parts). During the period of child growth, the pituitary gland doubles in weight (from 0.3 to 0.7 g).
The pineal gland (weight up to OD g) functions most actively until 7 years of age, and then degenerates into an inactive form. The pineal gland is considered the gland of childhood, since this gland produces the hormone GnRH, which inhibits the development of the gonads until a certain time. In addition, the pineal gland regulates water-salt metabolism, forming substances similar to hormones: melatonin, serotonin, norepinephrine, histamine. There is a certain cyclicity in the formation of pineal gland hormones during the day: melatonin is synthesized at night, and serotonin is synthesized at night. Due to this, it is believed that the pineal gland acts as a kind of chronometer of the body, regulating changes life cycles, and also ensures the relationship between a person’s own biorhythms and the rhythms of the environment.
The thyroid gland (weighing up to 30 grams) is located in front of the larynx in the neck. The main hormones of this gland are thyroxine, tri-iodothyronine, which influence the metabolism of water and minerals, on the go oxidative processes, on the processes of fat combustion, on height, body weight, on the physical and mental development of a person. The gland functions most actively at 5-7 and 13-15 years of age. The gland also produces the hormone Thyrocalcitonin, which regulates the exchange of calcium and phosphorus in the bones (inhibits their leaching from the bones and reduces the amount of calcium in the blood). With hypofunction of the thyroid gland, children are stunted in growth, their hair falls out, their teeth suffer, their psyche and mental development are impaired (the disease myxedema develops), and they lose their minds (cretinism develops). When the thyroid gland is overactive, it occurs Graves' disease signs of which are an enlarged thyroid gland, withdrawn eyes, sudden weight loss and a number of autonomic disorders ( increased heart rate, sweating, etc.). The disease is also accompanied by increased irritability, fatigue, decreased performance, etc.
Parathyroid glands (weight up to 0.5 g). The hormone of these glands is parathyroid hormone, which maintains the amount of calcium in the blood at a constant level (even, if necessary, by washing it out of the bones), and together with vitamin D, it affects the exchange of calcium and phosphorus in the bones, namely, it promotes the accumulation of these substances in fabric. Hyperfunction of the gland leads to super-strong mineralization of bones and ossification, as well as increased excitability of the cerebral hemispheres. With hypofunction, tetany (convulsions) is observed and bones soften. The endocrine system of the human body contains many important glands and this is one of them.
Thymus gland (thymus), like the bone marrow, is the central organ of immunogenesis. Individual red bone marrow stem cells enter the thymus through the bloodstream and in the gland structures undergo stages of maturation and differentiation, turning into T-lymphocytes (thymus-dependent lymphocytes). The latter again enter the bloodstream and spread throughout the body and create thymus-dependent zones in the peripheral organs of immunogenesis (spleen, lymph nodes etc.).. The thymus also creates a number of substances (thymosin, thymopoietin, thymic humoral factor, etc.), which most likely affect the processes of differentiation of G-lymphocytes. The processes of immunogenesis are described in detail in section 4.9.
The thymus is located in the sternum and has two compartments covered with connective tissue. The stroma (body) of the thymus has a reticular retina, in the loops of which thymic lymphocytes (thymocytes) and plasma cells (leukocytes, macrophages, etc.) are located. The body of the gland is conventionally divided into a darker (cortical) and medullary part. At the border of the cortex and brain parts large cells with high division activity (lymphoblasts) are isolated, which are considered germ points, because this is where stem cells come to mature.
The thymus gland of the endocrine system is active at 13-15 years of age- at this time it has the greatest mass (37-39g). After puberty, the mass of the thymus gradually decreases: at 20 years old it averages 25 g, at 21-35 years old - 22 g (V. M. Zholobov, 1963), and at 50-90 years old - only 13 g (W. Kroeman , 1976). Completely lymphoid tissue of the thymus does not disappear until old age, but most of it is replaced by connective (fatty) tissue: if in a newborn child connective tissue makes up to 7% of the mass of the gland, then at 20 years it reaches up to 40%, and after 50 years - 90%. The thymus gland is also capable of temporarily restraining the development of the gonads in children, and the hormones of the gonads themselves, in turn, can cause a reduction of the thymus.
The adrenal glands are located above the kidneys and weigh 6-8 g at birth., and in adults - up to 15 g each. These glands grow most actively during puberty, and finally mature at 20-25 years. Each adrenal gland has two layers of tissue: the outer (cortex) and the inner (medulla). These glands produce many hormones that regulate various processes in the body. Corticosteroids are formed in the cortex of the glands: mineralocorticoids and glucocorticoids, which regulate protein, carbohydrate, mineral and water-salt metabolism, affect the rate of cell reproduction, regulate the activation of metabolism during muscle activity and regulate the composition of blood cells (leukocytes). Gonadocorticosteroids (analogs of androgens and estrogens) are also produced, affecting the activity of sexual function and the development of secondary sexual characteristics (especially in childhood and old age). The adrenal medulla produces the hormones adrenaline and norepinephrine, which can activate the functioning of the entire body (similar to the action of the sympathetic division of the autonomic nervous system). These hormones are exclusively important to mobilize the body's physical reserves during stress, when performing physical exercise, especially during periods of hard work, intense sports training or competitions. With excessive excitement during sports performances, children can sometimes experience weakening of muscles, inhibition of reflexes to maintain body position, due to overexcitation of the sympathetic nervous system, as well as due to excessive release of adrenaline into the blood. In these circumstances, an increase in plastic muscle tone may also be observed, followed by numbness of these muscles or even numbness of spatial posture (the phenomenon of catalepsy).
The balance of the formation of GCS and mineralocorticoids is important. When insufficient glucocorticoids are produced, then hormonal balance shifts towards mineralocorticoids and this, by the way, can reduce the body’s resistance to the development of rheumatic inflammation in the heart and joints, to the development bronchial asthma. An excess of glucocorticoids suppresses inflammatory processes, but if this excess is significant, it can contribute to an increase in blood pressure, blood sugar (the development of so-called steroid diabetes) and can even contribute to the destruction of heart muscle tissue, the occurrence of ulcers of the stomach walls, etc.
. This gland, like the gonads, is considered mixed, since it performs exogenous (production of digestive enzymes) and endogenous functions. As an endogenous gland, the pancreas produces mainly the hormones glucagon and insulin, which affect carbohydrate metabolism in the body. Insulin lowers blood sugar, stimulates glycogen synthesis in the liver and muscles, promotes the absorption of glucose by muscles, retains water in tissues, activates protein synthesis and reduces the formation of carbohydrates from proteins and fats. Insulin also inhibits the formation of the hormone glucagon. The role of glucagon is opposite to the action of insulin, namely: glucagon increases blood sugar, including due to the conversion of tissue glycogen into glucose. With hypofunction of the gland, insulin production decreases and this can cause dangerous disease- diabetes. The development of pancreatic function continues until approximately 12 years of age in children and thus congenital disorders in her work often appear precisely during this period. Among other pancreatic hormones, lipocaine (promotes the utilization of fats), vagotonin (activates the parasympathetic part of the autonomic nervous system, stimulates the formation of red blood cells), centropein (improves the use of oxygen by the body's cells) should be highlighted.
In the human body, separate islands of glandular cells can be found in different parts of the body, forming analogues of endocrine glands and are called paraganglia. These glands usually produce local hormones that influence the course of certain functional processes. For example, enteroenzyme cells of the stomach walls produce hormones (hormones) gastrin, secretin, cholecystokinin, which regulate the processes of food digestion; the endocardium of the heart produces the hormone atriopeptide, which acts to reduce blood volume and pressure. The hormones erythropoietin (stimulates the production of red blood cells) and renin (affect blood pressure and influence the exchange of water and salts) are formed in the walls of the kidneys.
The endocrine system plays a very important role in the human body. She is responsible for growth and development mental abilities, controls the functioning of organs. However, the hormonal system does not work the same in adults and children.
Let's consider age-related features of the endocrine system
The formation of glands and their functioning begins during intrauterine development. The endocrine system is responsible for the growth of the embryo and fetus. During the formation of the body, connections are formed between the glands. After the birth of a child, they become stronger.
From the moment of birth until the onset of puberty, the greatest importance is thyroid, pituitary gland, adrenal glands. During puberty, the role of sex hormones increases. During the period from 10-12 to 15-17 years, many glands are activated. In the future, their work will stabilize. Subject to the right image life and absence of disease, there are no significant disruptions in the functioning of the endocrine system. The only exception is sex hormones.
The greatest importance in the process of human development is given to pituitary gland
It is responsible for the functioning of the thyroid gland, adrenal glands and other peripheral parts of the system. The mass of the pituitary gland in a newborn is 0.1-0.2 grams. At 10 years of age, its weight reaches 0.3 grams. The mass of the gland in an adult is 0.7-0.9 grams. The size of the pituitary gland may increase in women during pregnancy. While the baby is expecting, its weight can reach 1.65 grams.
Basic The function of the pituitary gland is considered to control body growth. It is performed through the production of growth hormone (somatotropic). If the pituitary gland does not work correctly at an early age, this can lead to an excessive increase in body weight and size or, conversely, to a small size.
The gland significantly influences the functions and role of the endocrine system, therefore, when it malfunction The production of hormones by the thyroid gland and adrenal glands is carried out incorrectly.
In early adolescence (16-18 years), the pituitary gland begins to work stably. If its activity does not return to normal, and somatotropic hormones are produced even after the body’s growth has completed (20-24 years), this can lead to acromegaly. This disease manifests itself in excessive enlargement of body parts.
Pineal gland– a gland that functions most actively until primary school age (7 years). Its weight in a newborn is 7 mg, in an adult – 200 mg. The gland produces hormones that inhibit sexual development. By the age of 3-7 years, the activity of the pineal gland decreases. During puberty, the number of hormones produced decreases significantly. Thanks to the pineal gland, human biorhythms are maintained.
Another important gland in the human body is thyroid. It begins to develop one of the first in the endocrine system. By the time of birth, the weight of the gland is 1-5 grams. At 15-16 years old, its weight is considered maximum. It is 14-15 grams. The greatest activity of this part of the endocrine system is observed at 5-7 and 13-14 years of age. After 21 years and up to 30 years, the activity of the thyroid gland decreases.
Parathyroid glands begin to form at the 2nd month of pregnancy (5-6 weeks). After the birth of a child, their weight is 5 mg. During her life, her weight increases 15-17 times. The greatest activity of the parathyroid gland is observed in the first 2 years of life. Then, until the age of 7, it is maintained at a fairly high level.
Thymus gland or thymus is most active during puberty (13-15 years). At this time, its weight is 37-39 grams. Its mass decreases with age. At 20 years old the weight is about 25 grams, at 21-35 - 22 grams.
The endocrine system in older people works less intensively, which is why the thymus gland decreases in size to 13 grams. As development progresses, the lymphoid tissues of the thymus are replaced by adipose tissues.
Adrenal glands At birth, the baby weighs approximately 6-8 grams each. As they grow, their weight increases to 15 grams. The formation of glands occurs up to 25-30 years. The greatest activity and growth of the adrenal glands is observed in 1-3 years, as well as during puberty. Thanks to the hormones that the gland produces, a person can control stress. They also affect the process of cell restoration, regulate metabolism, sexual and other functions.
Development pancreas occurs before age 12. Disturbances in its functioning are detected mainly in the period before the onset of puberty.
Female and male gonads are formed during intrauterine development. However, after the birth of a child, their activity is restrained until 10-12 years, that is, until the onset of the puberty crisis.
Male gonads - testicles. At birth, their weight is approximately 0.3 grams. From the age of 12-13, the gland begins to work more actively under the influence of gonadoliberin.
In boys, growth accelerates and secondary sexual characteristics appear. At the age of 15, spermatogenesis is activated. By the age of 16-17, the process of development of the male gonads is completed, and they begin to work in the same way as in an adult.
Female gonads - ovaries. Their weight at birth is 5-6 grams. The weight of the ovaries in adult women is 6-8 grams. The development of the gonads occurs in 3 stages. From birth to 6-7 years, a neutral stage is observed. During this period, the female-type hypothalamus is formed. The pre-pubertal period lasts from 8 years to the onset of adolescence. From the first menstruation to the onset of menopause, puberty is observed. At this stage, active growth occurs, the development of secondary sexual characteristics, and the formation of the menstrual cycle.
The endocrine system in children is more active compared to adults. The main changes in the glands occur at an early age, younger and older school age.
In order for the formation and functioning of the glands to be carried out correctly, it is very important to prevent disruptions to their functioning. The TDI-01 “Third Wind” simulator can help with this. You can use this device from the age of 4 and throughout your life. With its help, a person masters the technique of endogenous breathing. Thanks to this, it has the ability to maintain the health of the entire body, including the endocrine system.
Hormonal balance in the human body has a great influence on the nature of its higher nervous activity. There is not a single function in the body that is not influenced by the endocrine system, while at the same time the endocrine glands themselves are influenced by the nervous system. Thus, in the body there is a unified neuro-hormonal regulation of its vital functions.
Modern physiological data show that most hormones are capable of changing the functional state of nerve cells in all parts of the nervous system. For example, adrenal hormones significantly change the strength of neural processes. Removal of some parts of the adrenal glands in animals is accompanied by a weakening of the processes of internal inhibition and excitation processes, which causes profound disturbances in all higher nervous activity. Pituitary hormones in small doses increase higher nervous activity, and in large doses, inhibit it. Thyroid hormones in small doses enhance the processes of inhibition and excitation, and in large doses weaken the basic nervous processes. It is also known that hyper- or hypofunction of the thyroid gland causes gross disturbances in human higher nervous activity.
Significant impact on processes excitation and inhibition and the performance of nerve cells is influenced by sex hormones. Removal of the gonads in a person or their pathological underdevelopment causes a weakening of nervous processes and significant mental disorders. Castration in childhood often leads to mental disability. It has been shown that in girls, during the onset of menstruation, the processes of internal inhibition are weakened, the formation of conditioned reflexes worsens, and the level of general performance and school performance is significantly reduced. The clinic provides especially numerous examples of the influence of the endocrine sphere on the mental activity of children and adolescents. Damage to the hypothalamic-pituitary system and disruption of its functions most often occur in adolescence and are characterized by disorders of the emotional-volitional sphere and moral and ethical deviations. Teenagers become rude, angry, with a penchant for theft and vagrancy; Increased sexuality is often observed (L. O. Badalyan, 1975).
All of the above indicates the enormous role that hormones play in human life. An insignificant amount of them is already able to change our mood, memory, performance, etc. With a favorable hormonal background, “a person who previously seemed lethargic, depressed, unverbal, complaining of his weakness and inability to think...” wrote V. at the beginning of our century. M. Bekhterev, “becomes cheerful and lively, works a lot, creates various plans for his upcoming activities, declaring his excellent health, and the like.”
Thus, the connection between the nervous and endocrine regulatory systems, their harmonious unity are a necessary condition for the normal physical and mental development of children and adolescents.
Puberty It begins for girls at 8-9 years old, and for boys at 10-11 years old and ends at 16-17 and 17-18 years old, respectively. Its beginning appears in increased growth genitals. The degree of sexual development is easily determined by a set of secondary sexual characteristics: the development of pubic hair and axillary area, in young men - also on the face; in addition, in girls - by the development of the mammary glands and the time of the appearance of menstruation.
Sexual development of girls. In girls, puberty begins at primary school age, from 8-9 years. Sex hormones produced in the female gonads - the ovaries - are important for regulating the process of puberty (see section 3.4.3). By the age of 10, the weight of one ovary reaches 2 g, and by 14-15 years - 4-6 g, i.e. it practically reaches the weight of the ovary adult woman(5-6 g). Accordingly, the formation of female sex hormones in the ovaries, which have a general and specific effect on the girl’s body, is enhanced. The general effect is associated with the influence of hormones on metabolism and development processes in general. Under their influence, body growth accelerates, the development of skeletal and muscular systems occurs, internal organs etc. The specific action of sex hormones is aimed at the development of the genital organs and secondary sexual characteristics, which include: anatomical features of the body, features of the hairline, features of the voice, development of the mammary glands, sexual desire to the opposite sex, behavioral and mental characteristics.
In girls, enlargement of the mammary glands begins at the age of 10-11 years, and their development ends by the age of 14-15 years. The second sign of sexual development is the process of pubic hair growth, which appears at 11-12 years of age and reaches its final development at 14-15 years of age. The third main sign of sexual development - hair growth in the armpit - appears at 12-13 years of age and reaches its maximum development at 15-16 years of age. Finally, the first menstruation, or monthly bleeding, begins in girls on average at 13 years of age. Menstrual bleeding represents the final stage of the development cycle of an egg in the ovaries and its subsequent removal from the body. Usually this cycle is 28 days, but there are menstrual cycles of other durations: 21, 32 days, etc. Regular monthly cycles in 17-20% of girls are not established immediately, sometimes this process drags on for up to a year and a half or more, which is not a violation and does not require medical intervention. Serious violations include the absence of menstruation up to 15 years in the presence of excess hair or complete absence signs of sexual development, as well as sudden and heavy bleeding lasting more than 7 days.
With the onset of menstruation, the rate of body length growth in girls decreases sharply. In subsequent years until 15-16 years go by the final formation of secondary sexual characteristics and the development of the female body type, the growth of the body in length practically stops.
Sexual development of boys. Puberty in boys occurs 1-2 years later than in girls. The intensive development of their genital organs and secondary sexual characteristics begins at the age of 10-11 years. First of all, the size of the testicles, the paired male sex glands, rapidly increases, in which the formation of male sex hormones occurs, which also have a general and specific effect.
In boys, the first sign indicating the onset of sexual development should be considered “voice breaking” (mutation), which is most often observed from 11-12 to 15-16 years. The manifestation of the second sign of puberty - pubic hair - is observed from 12-13 years of age. The third sign - an increase in the thyroid cartilage of the larynx (Adam's apple) - appears from 13 to 17 years. And finally, last of all, from 14 to 17 years old, hair growth occurs in the armpit and face. In some adolescents, at the age of 17, secondary sexual characteristics have not yet reached their final development, and this continues in subsequent years.
At the age of 13-15 years, male reproductive cells - sperm - begin to be produced in the male gonads of boys, the maturation of which, unlike the periodic maturation of eggs, occurs continuously. At this age, most boys experience wet dreams - spontaneous ejaculation, which is a normal physiological phenomenon.
With the advent of wet dreams, boys experience a sharp increase in growth rates - the “third period of elongation” - which slows down from the age of 15-16. About a year after the growth spurt, the maximum increase in muscle strength occurs.
The problem of sex education for children and adolescents. With the onset of puberty in boys and girls, another one is added to all the difficulties of adolescence - the problem of their sex education. Naturally, it should begin already at primary school age and represent only an integral part of a single educational process. The outstanding teacher A. S. Makarenko wrote on this occasion that the issue of sex education becomes difficult only when it is considered separately and when it is given too much attention. great importance, distinguishing it from the general mass of other educational issues. It is necessary to form in children and adolescents correct ideas about the essence of the processes of sexual development, to cultivate mutual respect between boys and girls and their correct relationships. It is important for adolescents to form correct ideas about love and marriage, about family, and to familiarize them with the hygiene and physiology of sexual life.
Unfortunately, many teachers and parents try to “steer away” from the issues of sex education. This fact is confirmed by pedagogical research, according to which more than half of children and adolescents learn about many “delicate” issues of their sexual development from their older friends and girlfriends, about 20% from their parents and only 9% from teachers and educators.
Thus, sex education children and adolescents should be compulsory integral part their upbringing in the family. The passivity of the school and parents in this matter, their mutual hope for each other can only lead to the emergence of bad habits and misconceptions about the physiology of sexual development and the relationship between men and women. It is possible that many of the difficulties of subsequent family life newlyweds are caused by defects in improper sex education or its absence altogether. At the same time, all the difficulties of this “delicate” topic, which requires teachers, educators and parents to special knowledge, pedagogical and parental tact and certain pedagogical skills. To equip teachers and parents with all the necessary arsenal of sex education tools, special pedagogical and popular scientific literature is widely published in our country.
Parathyroid (parathyroid) glands. These are the four smallest endocrine glands. Their total weight is only 0.1 g. They are located in close proximity to the thyroid gland, and sometimes in its tissue.
Parathyroid hormone- hormone parathyroid glands plays a particularly important role in skeletal development, as it regulates the deposition of calcium in the bones and the level of its concentration in the blood. A decrease in calcium in the blood, associated with hypofunction of the glands, causes increased excitability of the nervous system, many disorders vegetative functions and skeletal formation. Rarely, hyperfunction of the parathyroid glands causes skeletal decalcification (“softening of the bones”) and deformation.
Thymus (thymus) gland. The thymus gland consists of two lobes located behind the sternum. Its morphofunctional properties change significantly with age. From birth to puberty, its weight increases and reaches 35-40 g. Then the process of degeneration of the thymus gland into adipose tissue. For example, by the age of 70, its weight does not exceed 6 g.
The belonging of the thymus gland to the endocrine system is still disputed, since its hormone has not been isolated. However, most scientists assume its existence and believe that this hormone affects the growth processes of the body, the formation of the skeleton and the immune properties of the body. There is also evidence of the influence of the thymus gland on the sexual development of adolescents. Its removal stimulates puberty, since it apparently has an inhibitory effect on sexual development. The connection between the thymus gland and the activity of the adrenal glands and thyroid gland has also been proven.
Adrenal glands. These are paired glands weighing about 4-7 g each, located on the upper poles of the kidneys. Morphologically and functionally, two qualitatively different parts of the adrenal glands are distinguished. The upper, cortical layer, the adrenal cortex, synthesizes about eight physiologically active hormones- corticosteroids: glucocorticoids, mineralocorticoids, sex hormones - androgens (male hormones) and estrogens (female hormones).
Glucocorticoids in the body they regulate protein, fat and especially carbohydrate metabolism, have an anti-inflammatory effect, and increase the body’s immune resistance. As the work of the Canadian pathophysiologist G. Selye has shown, glucocorticoids are important in ensuring the body's resistance to stress. Their number especially increases in the stage of resistance of the body, i.e., its adaptation to stressors. In this regard, it can be assumed that glucocorticoids play an important role in ensuring the full adaptation of children and adolescents to “school” stressful situations(arriving in 1st grade, moving to a new school, exams, test papers etc.).
Mineralocorticoids take part in the regulation of mineral and water metabolism; aldosterone is especially important among these hormones.
Androgens and estrogens in their action they are close to sex hormones synthesized in the sex glands - testes and ovaries, but their activity is significantly less. However, in the period before the onset of full maturation of the testes and ovaries, androgens and estrogens play a decisive role in the hormonal regulation of sexual development.
The inner, medulla layer of the adrenal glands synthesizes extremely important hormone- adrenaline, which has a stimulating effect on most body functions. Its action is very close to the action of the sympathetic nervous system: it speeds up and enhances the activity of the heart, stimulates energy transformations in the body, increases the excitability of many receptors, etc. All these functional changes help to increase the overall performance of the body, especially in “emergency” situations.
Thus, adrenal hormones largely determine the course of puberty in children and adolescents, provide the necessary immune properties of the child and adult body, participate in stress reactions, regulate protein, fat, carbohydrate, water and mineral metabolism. Adrenaline has a particularly strong effect on the functioning of the body. An interesting fact is that the content of many adrenal hormones depends on the physical fitness of the child’s body. A positive correlation has been found between adrenal activity and physical development children and teenagers. Physical activity significantly increases the content of hormones that provide protective functions body, and thereby contributes to optimal development.
Normal functioning of the body is possible only with an optimal ratio of the concentrations of various adrenal hormones in the blood, which is regulated by the pituitary gland and the nervous system. A significant increase or decrease in their concentration in pathological situations is characterized by disturbances in many body functions.
Epiphysis The influence of the hormone of this gland, also located near the hypothalamus, on the sexual development of children and adolescents has been discovered. Its damage causes premature puberty. It is assumed that the inhibitory effect of the pineal gland on sexual development occurs through blocking the formation of gonadotropic hormones in the pituitary gland. In an adult, this gland practically does not function. However, there is a hypothesis that the pineal gland is related to the regulation of " biological rhythms» human body.
Pancreas. This gland is located next to the stomach and duodenum. It belongs to the mixed glands: pancreatic juice is formed here, which plays an important role in digestion, and the secretion of hormones involved in the regulation of carbohydrate metabolism (insulin and glucagon) is also carried out here. One of endocrine diseases- diabetes mellitus - associated with hypofunction of the pancreas. Diabetes mellitus is characterized by a decrease in the level of the hormone insulin in the blood, which leads to a disruption in the absorption of sugar by the body and an increase in its concentration in the blood. In children, the manifestation of this disease most often occurs from 6 to 12 years. Hereditary predisposition and provoking environmental factors are important in the development of diabetes mellitus: infectious diseases, nervous overstrain and overeating. Glucagon, on the contrary, helps to increase blood sugar levels and is therefore an insulin antagonist.
Sex glands. The sex glands are also mixed. Here sex hormones are formed as reproductive cells. In the male sex glands - the testes - male sex hormones - androgens - are formed. A small amount of female sex hormones - estrogens - is also formed here. In the female sex glands - the ovaries - female sex hormones and a small amount of male hormones are formed.
Sex hormones largely determine the specific characteristics of metabolism in the female and male organisms and the development of primary and secondary sexual characteristics in children and adolescents.
Pituitary. The pituitary gland is the most important endocrine gland. It is located in close proximity to the diencephalon and has numerous bilateral connections with it. Up to 100 thousand nerve fibers have been discovered connecting the pituitary gland and the diencephalon (hypothalamus). This close proximity of the pituitary gland and the brain is a favorable factor for combining the “efforts” of the nervous and endocrine systems in regulating the vital functions of the body.
In an adult, the pituitary gland weighs approximately 0.5 g. At birth, its weight does not exceed 0.1 g, but by the age of 10 it increases to 0.3 g and reaches adult levels in adolescence. There are mainly two lobes in the pituitary gland: the anterior one, the adenohypophysis, which occupies about 75% of the size of the entire pituitary gland, and the posterior one, the pituitary gland, which accounts for about 18-23%. In children, the intermediate lobe of the pituitary gland is also distinguished, but in adults it is practically absent (only 1-2%).
About 22 hormones are known, produced mainly in the adenohypophysis. These hormones - triple hormones - have a regulatory effect on the functions of other endocrine glands: the thyroid, parathyroid, pancreas, reproductive and adrenal glands. They also influence all aspects of metabolism and energy, the processes of growth and development of children and adolescents. In particular, growth hormone (somatotropic hormone) is synthesized in the anterior lobe of the pituitary gland, which regulates the growth processes of children and adolescents. In this regard, hyperfunction of the pituitary gland can lead to a sharp increase in the growth of children, causing hormonal gigantism, and hypofunction, on the contrary, leads to significant growth retardation. Mental development is preserved at the same time normal level. Tonadotropic hormones of the pituitary gland (follicle-stimulating hormone - FSH, luteinizing hormone - LH, prolactin) regulate the development and function of the gonads, therefore, increased secretion causes acceleration of puberty in children and adolescents, and hypofunction of the pituitary gland causes delayed sexual development. In particular, FSH regulates the maturation of eggs in the ovaries in women, and spermatogenesis in men. LH stimulates the development of the ovaries and testes and the formation of sex hormones in them. Prolactin is important in the regulation of lactation processes in lactating women. Termination of the gonadotropic function of the pituitary gland due to pathological processes can lead to a complete stop of sexual development.
The pituitary gland synthesizes a number of hormones that regulate the activity of other endocrine glands, for example adrenocorticotropic hormone (ACTH), which increases the secretion of glucocorticoids, or thyroid-stimulating hormone, which increases the secretion of thyroid hormones.
Previously, it was believed that the neurohypophysis produces the hormones vasopressin, which regulates blood circulation and water metabolism, and oxytocin, which increases uterine contractions during childbirth. However, recent endocrinological data indicate that these hormones are a product of neurosecretion of the hypothalamus, from there they enter the neurohypophysis, which plays the role of a depot, and then into the blood.
Particularly important in the life of the body at any age is the interconnected activity of the hypothalamus, pituitary gland and adrenal glands, forming a single functional system - the hypothalamic-pituitary-adrenal system, functional value which is associated with the processes of adaptation of the body to stressors.
As shown special studies G. Selye (1936), the body's resistance to action unfavorable factors primarily depends on the functional state of the hypothalamic-pituitary-adrenal system. It is she who provides mobilization protective forces organism in stressful situations, which manifests itself in the development of the so-called general adaptation syndrome.
Currently, there are three phases, or stages, of the general adaptation syndrome: “anxiety”, “resistance” and “exhaustion”. The anxiety stage is characterized by activation of the hypothalamic-pituitary-adrenal system and is accompanied by increased secretion of ACTH, adrenaline and adaptive hormones (glucocorticoids), which leads to the mobilization of all energy reserves of the body. During the resistance stage, there is an increase in the body's resistance to adverse effects, which is associated with the transition of urgent adaptive changes into long-term ones, accompanied by functional and structural transformations in tissues and organs. As a result, the body’s resistance to stress factors is ensured not by increased secretion of glucocorticoids and adrenaline, but by increasing tissue resistance. In particular, athletes experience such long-term adaptation to heavy physical activity during training. With prolonged or frequent repeated exposure to stress factors, the development of the third phase, the exhaustion phase, is possible. This stage is characterized by a sharp drop in the body's resistance to stress, which is associated with disturbances in the activity of the hypothalamic-pituitary-adrenal system. Functional status the body at this stage deteriorates, and further exposure to unfavorable factors can lead to its death.
It is interesting to note that the functional formation of the hypothalamic-pituitary-adrenal system in the process of ontogenesis largely depends on motor activity children and teenagers. In this regard, it is necessary to remember that physical education and sports contribute to the development of the adaptive capabilities of the child’s body and are important factor preserving and strengthening the health of the younger generation.
Endocrine glands. The endocrine system plays an important role in regulating body functions. The organs of this system are endocrine glands– secrete special substances that have a significant and specialized effect on metabolism, structure and function of organs and tissues. Endocrine glands differ from other glands that have excretory ducts (exocrine glands) in that they secrete the substances they produce directly into the blood. That's why they are called endocrine glands (Greek endon - inside, krinein - to secrete).
The endocrine glands include the pituitary gland, pineal gland, pancreas, thyroid gland, adrenal glands, reproductive glands, parathyroid or parathyroid glands, and thymus gland.
Pancreas and gonads – mixed, since some of their cells perform an exocrine function, the other part - an intrasecretory function. The gonads produce not only sex hormones, but also germ cells (eggs and sperm). Some pancreatic cells produce the hormone insulin and glucagon, while other cells produce digestive and pancreatic juice.
Endocrine glands humans are small in size, have a very small mass (from fractions of a gram to several grams), are richly supplied blood vessels. Blood brings the necessary building material to them and carries away chemically active secretions.
TO endocrine glands an extensive network of nerve fibers approaches, their activity is constantly controlled by the nervous system.
The endocrine glands are functionally closely related to each other, and damage to one gland causes dysfunction of other glands.
Thyroid. During ontogenesis, the mass of the thyroid gland increases significantly - from 1 g during the newborn period to 10 g by the age of 10 years. With the onset of puberty, the growth of the gland is especially intense, during the same period the functional tension of the thyroid gland increases, as evidenced by a significant increase in the content of total protein, which is part of the thyroid hormone. The content of thyrotropin in the blood increases rapidly up to 7 years of age.
An increase in the content of thyroid hormones is noted by the age of 10 and at the final stages of puberty (15-16 years). At the age of 5-6 to 9-10 years, the pituitary-thyroid relationship changes qualitatively; the sensitivity of the thyroid gland to thyroid-tropic hormones decreases, the greatest sensitivity to which is noted at 5-6 years. This indicates that the thyroid gland is especially important for the development of the body at an early age.
Insufficiency of thyroid function in childhood leads to cretinism. At the same time, growth is delayed and body proportions are disturbed, sexual development is delayed, and mental development lags behind. Early detection hypofunction of the thyroid gland and appropriate treatment have a significant positive effect.
Adrenal glands. From the first weeks of life, the adrenal glands are characterized by rapid structural transformations. The development of adrenal measles occurs intensively in the first years of a child’s life. By the age of 7, its width reaches 881 microns, at 14 years it is 1003.6 microns. At birth, the adrenal medulla consists of immature nerve cells. During the first years of life, they quickly differentiate into mature cells called chromophilic cells, as they are distinguished by their ability to stain yellow chrome salts. These cells synthesize hormones, the action of which has much in common with the sympathetic nervous system - catecholamines(adrenaline and norepinephrine). Synthesized catecholamines are contained in the medulla in the form of granules, from which they are released under the influence of appropriate stimuli and enter the venous blood flowing from the adrenal cortex and passing through the medulla. Stimuli for the entry of catecholamines into the blood are excitement, irritation of the sympathetic nerves, physical activity, cooling, etc. The main hormone of the medulla is adrenalin, it makes up approximately 80% of the hormones synthesized in this part of the adrenal glands. Adrenaline is known as one of the fastest-acting hormones. It accelerates blood circulation, strengthens and increases heart rate; improves pulmonary respiration, dilates the bronchi; increases the breakdown of glycogen in the liver, the release of sugar into the blood; enhances muscle contraction, reduces fatigue, etc. All these effects of adrenaline lead to one thing overall result– mobilization of all the body’s forces to perform hard work.
Increased secretion of adrenaline is one of the most important mechanisms of restructuring in the functioning of the body in extreme situations, when emotional stress, sudden physical exertion, during cooling.
The close connection of the chromophilic cells of the adrenal gland with the sympathetic nervous system determines the rapid release of adrenaline in all cases when circumstances arise in a person’s life that require him to urgently exert his strength. A significant increase in functional tension of the adrenal glands is observed by the age of 6 and during puberty. At the same time, the content of steroid hormones and catecholamines in the blood increases significantly.
Pancreas. In newborns, the intrasecretory tissue of the pancreas predominates over the exocrine tissue. The islets of Langerhans increase significantly in size with age. Islands of large diameter (200-240 µm), characteristic of adults, are detected after 10 years. An increase in the level of insulin in the blood in the period from 10 to 11 years has also been established. The immaturity of the hormonal function of the pancreas may be one of the reasons that diabetes mellitus in children is most often detected between the ages of 6 and 12 years, especially after acute illnesses. infectious diseases(measles, chicken pox, mumps). It has been noted that the development of the disease is facilitated by overeating, especially excess rich in carbohydrates food.
