The Endocrine System and Glands of the Human Body: Function and Disorders

Written by Barbara Brody

• What Is the Endocrine System?
• What Is a Gland?
• Endocrine System Functions
• Parts of the Endocrine System
• Health Issues
• Endocrine System Disorders
• More

The endocrine system is a network of glands in your body that make the hormones that help cells talk to each other. They’re responsible for almost every cell, organ, and function in your body.

If your endocrine system isn’t healthy, you might have problems developing during puberty, getting pregnant, or managing stress. You also might gain weight easily, have weak bones, or lack energy because too much sugar stays in your blood instead of moving into your cells where it’s needed for energy.

A gland is an organ that makes and puts out hormones that do a specific job in your body. Endocrine and exocrine glands release the substances they make into your bloodstream.

Your endocrine system:

• Makes hormones that control your moods, growth and development, metabolism, organs, and reproduction
• Controls how your hormones are released
• Sends those hormones into your bloodstream so they can travel to other body parts

Many glands make up the endocrine system. The hypothalamus, pituitary gland, and pineal gland are in your brain. The thyroid and parathyroid glands are in your neck. The thymus is between your lungs, the adrenals are on top of your kidneys, and the pancreas is behind your stomach. Your ovaries (if you’re a woman) or testes (if you’re a man) are in your pelvic region.

• Hypothalamus. This organ connects your endocrine system with your nervous system. Its main job is to tell your pituitary gland to start or stop making hormones.
• Pituitary gland. This is your endocrine system’s master gland. It uses information it gets from your brain to tell other glands in your body what to do. It makes many important hormones, including growth hormone; prolactin, which helps breastfeeding moms make milk; antidiuretic hormone(ADH) (vasopressin), which controls blood pressure and helps control body water balance through its effect on the kidney, corticotropin /ACTH: Adrenocorticotrophic hormone. which stimulates the adrenal gland to make certain hormones, thyroid-stimulating hormone (TSH), which stimulates the production and secretion of thyroid hormones, oxytocin which helps in milk ejection during breast feeding; and luteinizing hormone, which manages estrogen in women and testosterone in men.
• Pineal gland. It makes a chemical called melatonin that helps your body get ready to go to sleep.
• Thyroid gland. This gland makes thyroid hormone, which controls your growth and metabolism. If this gland doesn’t make enough (a condition called hypothyroidism), everything happens more slowly. Your heart rate might slow down. You could get constipated. And you might gain weight. If it makes too much (hyperthyroidism), everything speeds up. Your heart might race. You could have diarrhea. And you might lose weight without trying. The thyroid gland also produces the hormone calcitonin, which may contribute to bone strength by helping calcium to be incorporated into bone.
• Parathyroid. This is a set of four small glands behind your thyroid. They play a role in bone health. The glands control your levels of calcium and phosphorus.
• Thymus. This gland makes white blood cells called T-lymphocytes that fight infection and are crucial as a child’s immune system develops. The thymus starts to shrink after puberty.
• Adrenals. Best known for making the “fight or flight” hormone adrenaline (also called epinephrine), these two glands also make hormones called corticosteroids. They affect your metabolism heart rate, oxygen intake, blood flow, and sexual function, among other things.
• Pancreas. This organ is part of both your digestive and endocrine systems. It makes digestive enzymes that break down food. It also makes the hormones insulin and glucagon. These ensure you have the right amount of sugar in your bloodstream and your cells.
• If you don’t make insulin, which is the case for people with type 1 diabetes, your blood sugar levels can get dangerously high. In type 2 diabetes, the pancreas usually makes some insulin but not enough.
• Ovaries. In women, these organs make estrogen and progesterone. These hormones help develop breasts at puberty, regulate the menstrual cycle, and support a pregnancy.
• Testes. In men, the testes make testosterone. It helps them grow facial and body hair at puberty. It also tells the penis to grow larger and plays a role in making sperm.

As you get older, it’s natural to notice some things related to your endocrine system. Your metabolism tends to slow down. So you might gain weight even though you haven’t changed how you eat or exercise. Hormonal shifts also explain, at least in part, why you’re more likely to have heart disease, osteoporosis, and type 2 diabetes as you age.

No matter how old you are, stress, infections, and being around certain chemicals can also mess with parts of your endocrine system. And genetics or lifestyle habits can increase your chances of an endocrine disorder like hypothyroidism, diabetes, or osteoporosis.

• Acromegaly. Sometimes the pituitary gland makes too much growth hormone and your bones get bigger. It usually affects your hands, feet, and face. It usually starts in middle age.
• Adrenal insufficiency. When you have this, your adrenal glands don’t make enough of certain hormones, like cortisol, which controls stress.
• Cushing’s disease. In this, your body makes too much cortisol. You could gain weight, get stretch marks, bruise easily at first, then get weakened muscles and bones and possibly develop a hump on your upper back.
• Hyperthyroidism. This is when your thyroid gland makes more hormones than your body needs. You might hear it called overactive thyroid. It makes your system run fast and you might feel nervous, lose weight, and have a rapid heartbeat or trouble sleeping.
• Hypothyroidism. When your body doesn’t make enough thyroid hormone, your system slows down. You might feel tired, gain weight, have a slow heartbeat, and get joint and muscle pains.
• Hypopituitarism. Sometimes your pituitary gland doesn’t make enough of certain hormones and your adrenal and thyroid glands can’t work right.
• Multiple endocrine neoplasia. This is a group of disorders that affect your endocrine system. It causes tumors on at least two endocrine glands or in other organs and tissues.
• Polycystic ovary syndrome. An imbalance of reproductive hormones can cause your ovaries to either not make an egg or not release it during ovulation. This can throw off your periods, cause acne, and make hair to grow on your face or chin.
• Precocious puberty. When glands that control reproduction don’t work properly, some kids start puberty abnormally early — around 8 in girls and 9 in boys.

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The Endocrine System and Glands of the Human Body: Function and Disorders

Written by Barbara Brody

• What Is the Endocrine System?
• What Is a Gland?
• Endocrine System Functions
• Parts of the Endocrine System
• Health Issues
• Endocrine System Disorders
• More

The endocrine system is a network of glands in your body that make the hormones that help cells talk to each other. They’re responsible for almost every cell, organ, and function in your body.

If your endocrine system isn’t healthy, you might have problems developing during puberty, getting pregnant, or managing stress. You also might gain weight easily, have weak bones, or lack energy because too much sugar stays in your blood instead of moving into your cells where it’s needed for energy.

A gland is an organ that makes and puts out hormones that do a specific job in your body. Endocrine and exocrine glands release the substances they make into your bloodstream.

Your endocrine system:

• Makes hormones that control your moods, growth and development, metabolism, organs, and reproduction
• Controls how your hormones are released
• Sends those hormones into your bloodstream so they can travel to other body parts

Many glands make up the endocrine system. The hypothalamus, pituitary gland, and pineal gland are in your brain. The thyroid and parathyroid glands are in your neck. The thymus is between your lungs, the adrenals are on top of your kidneys, and the pancreas is behind your stomach. Your ovaries (if you’re a woman) or testes (if you’re a man) are in your pelvic region.

• Hypothalamus. This organ connects your endocrine system with your nervous system. Its main job is to tell your pituitary gland to start or stop making hormones.
• Pituitary gland. This is your endocrine system’s master gland. It uses information it gets from your brain to tell other glands in your body what to do. It makes many important hormones, including growth hormone; prolactin, which helps breastfeeding moms make milk; antidiuretic hormone(ADH) (vasopressin), which controls blood pressure and helps control body water balance through its effect on the kidney, corticotropin /ACTH: Adrenocorticotrophic hormone. which stimulates the adrenal gland to make certain hormones, thyroid-stimulating hormone (TSH), which stimulates the production and secretion of thyroid hormones, oxytocin which helps in milk ejection during breast feeding; and luteinizing hormone, which manages estrogen in women and testosterone in men.
• Pineal gland. It makes a chemical called melatonin that helps your body get ready to go to sleep.
• Thyroid gland. This gland makes thyroid hormone, which controls your growth and metabolism. If this gland doesn’t make enough (a condition called hypothyroidism), everything happens more slowly. Your heart rate might slow down. You could get constipated. And you might gain weight. If it makes too much (hyperthyroidism), everything speeds up. Your heart might race. You could have diarrhea. And you might lose weight without trying. The thyroid gland also produces the hormone calcitonin, which may contribute to bone strength by helping calcium to be incorporated into bone.
• Parathyroid. This is a set of four small glands behind your thyroid. They play a role in bone health. The glands control your levels of calcium and phosphorus.
• Thymus. This gland makes white blood cells called T-lymphocytes that fight infection and are crucial as a child’s immune system develops. The thymus starts to shrink after puberty.
• Adrenals. Best known for making the “fight or flight” hormone adrenaline (also called epinephrine), these two glands also make hormones called corticosteroids. They affect your metabolism heart rate, oxygen intake, blood flow, and sexual function, among other things.
• Pancreas. This organ is part of both your digestive and endocrine systems. It makes digestive enzymes that break down food. It also makes the hormones insulin and glucagon. These ensure you have the right amount of sugar in your bloodstream and your cells.
• If you don’t make insulin, which is the case for people with type 1 diabetes, your blood sugar levels can get dangerously high. In type 2 diabetes, the pancreas usually makes some insulin but not enough.
• Ovaries. In women, these organs make estrogen and progesterone. These hormones help develop breasts at puberty, regulate the menstrual cycle, and support a pregnancy.
• Testes. In men, the testes make testosterone. It helps them grow facial and body hair at puberty. It also tells the penis to grow larger and plays a role in making sperm.

As you get older, it’s natural to notice some things related to your endocrine system. Your metabolism tends to slow down. So you might gain weight even though you haven’t changed how you eat or exercise. Hormonal shifts also explain, at least in part, why you’re more likely to have heart disease, osteoporosis, and type 2 diabetes as you age.

No matter how old you are, stress, infections, and being around certain chemicals can also mess with parts of your endocrine system. And genetics or lifestyle habits can increase your chances of an endocrine disorder like hypothyroidism, diabetes, or osteoporosis.

• Acromegaly. Sometimes the pituitary gland makes too much growth hormone and your bones get bigger. It usually affects your hands, feet, and face. It usually starts in middle age.
• Adrenal insufficiency. When you have this, your adrenal glands don’t make enough of certain hormones, like cortisol, which controls stress.
• Cushing’s disease. In this, your body makes too much cortisol. You could gain weight, get stretch marks, bruise easily at first, then get weakened muscles and bones and possibly develop a hump on your upper back.
• Hyperthyroidism. This is when your thyroid gland makes more hormones than your body needs. You might hear it called overactive thyroid. It makes your system run fast and you might feel nervous, lose weight, and have a rapid heartbeat or trouble sleeping.
• Hypothyroidism. When your body doesn’t make enough thyroid hormone, your system slows down. You might feel tired, gain weight, have a slow heartbeat, and get joint and muscle pains.
• Hypopituitarism. Sometimes your pituitary gland doesn’t make enough of certain hormones and your adrenal and thyroid glands can’t work right.
• Multiple endocrine neoplasia. This is a group of disorders that affect your endocrine system. It causes tumors on at least two endocrine glands or in other organs and tissues.
• Polycystic ovary syndrome. An imbalance of reproductive hormones can cause your ovaries to either not make an egg or not release it during ovulation. This can throw off your periods, cause acne, and make hair to grow on your face or chin.
• Precocious puberty. When glands that control reproduction don’t work properly, some kids start puberty abnormally early — around 8 in girls and 9 in boys.

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Functions of the endocrine glands in the human body.

Tests for hormones and their interpretation.

The human endocrine system consists of organs called endocrine glands, which regulate the work of the whole organism by releasing biologically active substances – hormones – into the circulatory system. These substances perform paramount functions in the body: they help maintain homeostasis, control growth and development, participate in metabolic processes, are responsible for responding to changes in environmental conditions, and regulate the reproductive system.

Endocrine glands include:

Thyroid. Produces hormones – thyroxine (T4), triiodothyronine (T3), calcitonin. These hormones are involved in metabolism, increasing its intensity, regulate growth processes in the body, increase the level of consumption of vital oxygen by organs and tissues.

Parathyroid glands. They produce parathyroid hormone that regulates the level of calcium in the body, which is necessary for the normal functioning of the motor apparatus and nervous system.

Thymus (thymus). This organ occupies a central place in the human immune system, not without reason the word “thymus” is translated from ancient Greek as “life force”. The thymus produces T-lymphocytes – immune cells that provide antiviral and antitumor protection of the body. It secretes a number of hormones into the blood: thymalin, thymosin, IGF-1, thymopoietin, which are responsible for the functional activity of the immune system.

Adrenals. They produce the so-called stress hormone – adrenaline, which is involved in the body’s response to external stressful situations. When a large amount of adrenaline is released into the blood, breathing quickens, the heart rate increases, blood vessels constrict, and the pupils dilate.

Pancreas. Is the main source of enzymes for the digestion of fats, proteins and carbohydrates. It produces the hormones insulin, which lowers the level of glucose in the blood, and glucagon, on the contrary, increases it.

Gonads. In women, the ovaries; in men, the testes. The hormones produced by these glands are responsible for reproductive function.

Pituitary and hypothalamus. Form the hypothalamic-pituitary system. The pituitary gland produces hormones that control almost the entire endocrine system. Among them, the most important is the growth hormone – somatotropin, which affects the growth of bones, cartilage and muscles.

Epiphysis (pineal body, or pineal gland). The organ performs important functions: it slows down growth hormones, inhibits the development of tumors, and affects sexual development. It produces antidiuretic hormone (ADH), which controls the water balance of the body, oxytocin, which is responsible for muscle contraction, and melatonin, a hormone that controls the sequence of sleep phases.

Based on the foregoing, we can follow the conclusion that the importance of the endocrine system cannot be overestimated – its activity extends to all organs of the body and all processes occurring in it. Therefore, all deviations from the norm in the operation of this system require immediate medical intervention.

Symptoms of hormonal imbalance

There are a lot of symptoms of malfunctioning of the endocrine glands, among them are:

• Irregular or absent menstruation in women;
• Miscarriage or infertility;
• Loss of sexual desire;
• Weight gain;
• Eruptions on the body, acne;
• Deterioration of hair and nails;
• Sleep disturbances, lethargy, increased fatigue;
• Emotional instability: tearfulness, irascibility, nervousness;
• The development of osteoporosis is a disease that leads to brittle bones.

It is worth noting that none of the above symptoms is a direct confirmation of the presence of a hormonal imbalance, but only a possible consequence. To make an accurate diagnosis, it is necessary to undergo a complete examination by an endocrinologist, which includes the method of functional diagnostics (ultrasound, MRI), as well as laboratory blood tests, which will be discussed below.

How is blood tested for hormones?

A blood test for hormones is the most indicative and informative method for detecting any pathologies in the work of the endocrine glands. However, it is important to consider that many factors influence the hormonal background: the time of day, the menstrual cycle in women, and medication. For this reason, the preparation for taking tests for a hormonal study must be taken with all seriousness. If this is neglected, then the result of the analysis may be incorrect and, at best, it will have to be retaken, and at worst, an incorrect diagnosis may be made on its basis and the wrong treatment may be prescribed, which can lead to irreparable consequences.

To prepare for donating blood for hormones, the following general rules must be observed:

• On the eve of the test, you should give up physical activity, try to avoid stressful situations, stop any physiotherapy procedures, exclude oral contraceptives, alcohol, fatty foods and products containing iodine. It is also recommended to postpone the ECG, ultrasound, x-ray examination for a while after the test.
• An important point is taking medications – it is necessary to notify the doctor who ordered the hormonal blood test about the fact of taking medications. He will decide whether to cancel or continue taking medications at the time of the test.
• An analysis for a hormonal study is given strictly on an empty stomach. Therefore, it is recommended to stop eating 12 hours before blood sampling.
• In the morning, before the test, it is forbidden to chew gum, drink tea and smoke.
• Just before donating blood, rest for 15-10 minutes.
• Women need to take into account their menstrual cycle, because. it is possible to examine the blood for some hormones only in certain periods of this cycle.
• To track the dynamics of the levels of certain hormones, a second analysis is required. It is rented at approximately the same time as the previous one, in compliance with all the above rules.

Blood sampling for analysis is carried out in the first half of the day in the morning. The biomaterial is taken from the cubital vein.

Explanation of tests

Thyroid hormones

Triiodothyronine , or T3 – gives a general assessment of the work of the thyroid gland. This hormone is determined both in free form (norm: from 2.6 to 5.7 pmol/l.), And in the serum state, (general form; norm: from 1.3 to 2.7 nmol/l). An increase in the indicator indicates the use of narcotic substances: methadone, heroin, amphetamine, HIV infection, renal failure, hyperthyroidism. The decrease was established with the use of androgens, danazol, dexamethasone, propranolol.

Thyroxine , or T4 – regulates energy metabolism in the body. Norm: 10.8 – 22.0 pmol / l. A low level is observed with hyperthyroidism, hemolysis. Elevated levels – when taking oral contraceptives, methodone, heroin, estrogen.

Thyroglobulin , or Tg – is prescribed for suspected malignant neoplasms. Norm: < 55 ng / ml.

Antibodies to thyroglobulin – are prescribed for suspected autoimmune thyroid diseases. Norm: 0 – 18 U / ml.

Microsomal antibodies are the most accurate indicator of the presence of autoimmune diseases. A deviation from the norm < 5.6 U / ml is proof of the aggression of the immune system to its own body.

Thyroxine-binding globulin , or TSH, is responsible for the transport of the hormones T3 and T4. Norm: from 16.8 to 22.5 mcg / ml. An increased indicator may indicate pregnancy, a lower one – with cirrhosis of the liver.

Adrenal hormones

Cortisol – regulates carbohydrate metabolism. Norm: from 230 to 750 nm / l. A low rate may be the result of chronic adrenal insufficiency, and a high one may indicate oncology or adenoma.

Aldosterone – responsible for the water-salt balance. Norms: in a horizontal position 17. 6-230.2 pg / ml; in a vertical position 25.2-392 pg / ml. Elevated levels of the hormone in the blood usually indicate an adrenal tumor.

Norepinephrine and epinephrine – normalize heart rate, blood pressure, form glucose levels. Norms: from 1.92 to 2.46 nm / l for adrenaline, from 0.62 to 3.23 nm / l for norepinephrine. An increase in indicators indicates kidney disease, Itsenko-Cushing’s syndrome, emotional and physical workload of the body, a decrease indicates pathology of the hypothalamus.

Sex hormones

Estradiol – is responsible for the production of germ cells and the proper development of pregnancy. The norm in the first phase of the menstrual cycle (follicular phase) is from 200 to 285 pm/l, the norm in the corpus luteum phase (luteal phase) is from 440 to 575 pi/l, during menopause from 50 to 133 pm/l. A lower indicator may indicate a tumor in the ovaries, an increased indicator – with their insufficient functioning.

Testosterone is the main male hormone. Responsible for the formation of secondary sexual characteristics, stimulates the growth of muscle mass and bones. Norms: for men – 2 -10 ng / ml, for women – 0.2 – 1 ng / l.

Progesterone – ensures the proper development of the genital organs in women. The norm in the first phase of the menstrual cycle (follicular phase) is from 1 to 2.2 nm / l, the norm in the corpus luteum phase (luteal phase) is from 23 to 30 nm / l, during menopause from 1 to 1.8 nm / l. An increase in the indicator is observed with tumors of the adrenal cortex, a decrease – with ovarian sclerosis.

Pituitary hormones

Thyroid stimulating hormone , or TSH, stimulates the production of the main thyroid hormones, so deviations from the reference values ​​​​indicate thyroid dysfunction. Norm: 0.4-4.0 honey / l.

Somatotropic hormone , or STH – a hormone of the anterior pituitary gland, is responsible for stimulating the mouth of bones, muscle mass and other organs of the human body. Norm: < 10.0 ng / ml. Exceeding the value of the established norm indicates gigantism, acromegaly.

Adrenocorticotropic hormone , or ACTH – stimulates the synthesis of hormones in the adrenal cortex. Norm: < 46 pg / ml. Deviations from the norm are observed in Itsenko-Cushing's syndrome, Addison's disease, as well as in other disorders of the adrenal glands.

Prolactin is a hormone responsible for the growth of the mammary glands in women and the functioning of the prostate in men. The norm for the stronger sex is 100 – 265 mcg / l, for the fair sex – from 130 to 540 skg / l during the childbearing period.

Follicle-stimulating hormone , FSH – stimulates the growth of follicles in women, is responsible for the functioning of the seminiferous tubules in men. The norm in women: in the first phase of the menstrual cycle (follicular phase) from 1.37 – 9.90 IU / l, in the corpus luteum phase (luteal phase) from 1. 09 – 9.20 IU / ml, during menopause from 29.5 to 55 IU / l, during ovulation from 2.7 to 6.7 IU / ml. The norm for men: 0.95 – 11.95 mU / ml.

Luteinizing hormone , or LH – stimulates the production of testosterone in men, progesterone in women. Normal values ​​for men: from 1.14 to 8.75 mU / ml. Norm for women: in the follicular phase from 1.68 to 15.00 mU / ml, in the ovulatory phase from 21.90 – 56.60 mU / ml, in the luteal phase: 0.61 – 16.30 mU / ml, in postmenopausal women from 14.20 – 52.30 mU / ml. Deviations from normal values ​​in both sexes indicate dysfunction of the gonads.

Biology Endocrine glands and their functions

Human organ systems perform strictly defined functions, and in order for the body to exist as a whole, it is necessary to regulate and coordinate this complex work. This regulation is carried out by the nervous and humoral systems. Humoral regulation is carried out due to the release of hormones into the internal environment of the body, which are produced by the endocrine glands.

Endocrine glands, or endocrine glands, do not have excretory ducts. The products of their vital activity – hormones – they secrete into the internal environment of the body: into the blood, lymph or tissue fluid. it is formed by endocrine glands. While the glands of external secretion – sweat, salivary, sebaceous, gastric – secrete the products of their vital activity into the external environment or body cavities.

Entering the blood, the hormone is distributed throughout the body and carries out humoral regulation of the functions of organs and tissues, changing their activity, stimulating or inhibiting their work.

The most important endocrine glands are the thyroid, parathyroid, thymus, adrenal and pituitary glands.

There are also glands of mixed secretion in the body, which produce several waste products. Some of them enter the bloodstream, and some go through the ducts into the cavity of the internal organs. This type of gland includes the pancreas and gonads.

The product of the vital activity of the endocrine glands is a hormone. The term “hormone” (from the Greek “I excite”, “I induce”) was introduced into practice by W. Bayliss and E. Starling. January 1902, they conducted an experiment that convincingly proved the participation of the humoral factor in the regulation of the secretory activity of the pancreas. According to Bayliss and Starling, a hormone is any substance normally produced by the cells of any part of the body and carried by the blood to the distant parts on which it acts.

Currently, hormones are defined as highly active substances formed in the endocrine glands, entering the bloodstream and exerting a regulatory influence on the functions of organs and body systems remote from their place of secretion.

According to the chemical structure, hormones are divided into:

– hormones – derivatives of amino acids;

– protein and polypeptide hormones;

– steroid hormones.

According to the physiological effect – on launchers and performers. Trigger hormones (activators of the activity of other endocrine glands) include neurohormones of the hypothalamus and tropic hormones of the pituitary gland. Hormones-performers have a direct effect on the functions of the body.

Hormones are distinguished by a strict specificity of action – the reactions of organs, tissues and cells to them are strictly selective. Hormones act even in negligible amounts, but they are quickly destroyed, and therefore must be synthesized by the glands as needed and enter the bloodstream.

The thyroid gland is the largest of the endocrine glands, its mass is 16-23 g. It is located on both sides of the trachea just below the thyroid cartilage of the larynx. Thyroid hormones (thyroxine and triiodothyronine) contain iodine. Its intake with water and food is a necessary condition for the normal functioning of the gland.

Thyroid hormones regulate metabolism, enhance oxidative processes in cells and the breakdown of glycogen in the liver, affect the growth, development and differentiation of tissues, as well as the activity of the nervous system.

The adrenal glands are paired glands adjacent to the upper poles of the kidneys. Like the kidneys, the adrenal glands have two layers: the outer one is the cortical layer, and the inner one is the medulla, which are independent secretory organs. They produce different hormones with different patterns of action.

The cells of the cortical layer synthesize cortisol and corticosterone, which regulate mineral, carbohydrate, protein and fat metabolism. So, with their participation, the level of sodium and potassium in the blood is regulated, a certain concentration of glucose is maintained, the formation and deposition of glycogen in the liver and muscles increases. The last two functions of the adrenal glands are performed in conjunction with pancreatic hormones.

The adrenal medulla produces adrenaline and norepinephrine, which are released during strong emotions – anger, fear, pain, danger. The entry of these hormones into the blood causes a rapid heartbeat, narrowing of blood vessels, increased blood pressure, increased breakdown of glycogen in liver cells and muscles to glucose, inhibition of intestinal motility, relaxation of bronchial muscles, increased excitability of retinal receptors, auditory and vestibular apparatus. As a result, the functions of the body are rebuilt, forces are mobilized to endure stressful situations.

The pancreas is a mixed secretion gland. It has special islet cells that produce insulin and glucagon, which regulate carbohydrate metabolism in the body. So, insulin increases the consumption of glucose by cells, promotes the conversion of glucose into glycogen, thus reducing the amount of sugar in the blood. Due to the action of insulin, the blood glucose content is maintained at a constant level, favorable for the flow of vital processes.

Another pancreatic hormone – glucagon – is an insulin antagonist, has the opposite effect, that is, it enhances the breakdown of glycogen to glucose, increasing its content in the blood.

The gonads, the testes, or testicles in men and the ovaries in women, are glands of mixed secretion. The testicles produce androgens and the ovaries produce estrogens. They stimulate the development of reproductive organs, the maturation of germ cells and the formation of secondary sexual characteristics, that is, the structural features of the skeleton, the development of muscles, the distribution of hairline and subcutaneous fat, the structure of the larynx, the timbre of the voice in men and women.

The most important gland of the human endocrine system is the pituitary gland, or the lower appendage of the brain weighing only 0.5 g. It is located at the base of the brain – in the so-called “Turkish saddle”. The pituitary gland produces hormones that stimulate the functions of other endocrine glands.

In the pituitary gland, there are two main sections: the anterior lobe – adenohypophysis and the posterior – neurohypophysis, each of them produces certain hormones. So, in the anterior pituitary gland, hormones are produced that stimulate the synthesis and secretion of thyroid hormones (thyrotropin), adrenal glands (adrenocorticotropin), gonads (gonadotropin), as well as growth hormone (somatotropin).

Vasopressin and oxytocin are synthesized in the posterior pituitary gland. Vasopressin, or antidiuretic hormone, regulates water metabolism and vascular tone. Oxytocin increases the tone of the smooth muscles of the uterus, regulates the birth act and the secretion of milk by the mammary glands.

The pituitary gland is located directly below the hypothalamus and is connected to it by a funnel and stalk. The hypothalamus is a part of the brain that has properties of the nervous and endocrine systems. The hypothalamus receives an extensive flow of information from the senses and internal organs. The composition of the neurosecretory nuclei of the hypothalamus includes the so-called large and small cell nuclei. The former secrete oxytocin and vasopressin, which are transported along the nerve trunks to the posterior pituitary gland, accumulate there and are used as needed. Other functions are performed by the small cell nuclei of the hypothalamus. They are able to develop the so-called releasing factors (allowing factors). Releasing factors through the venous system reach the pituitary gland and regulate the release of hormones of the latter.

All endocrine glands are interconnected. Hormones produced by some glands affect the activity of other glands. This provides a unified system of coordination, which is carried out according to the feedback principle: a decrease in the level of a peripheral hormone in the blood leads to an increase in the secretion of the corresponding tropic hormone, and an increase in the level of a peripheral hormone causes inhibition of the secretion of the tropic hormone.