Endocrine system is formed of the endocrine glands that produce in an organism the physiologically active substances - hormones, and have no excretory ducts. Hormones are able to amplify and supress the function of cells, tissues, organs, and thereby endocrine glands, together with the nervous system and under its control perform humoral regulatory function, ensuring a coherent work of the whole organism.
Endocrine glands have no excretory ducts. EG's produce secretion or hormones.

Endocrine glands include:
• Thyroid gland
• Parathyroid gland
• Thymus
• The pancreas (its endocrine part)
• Adrenal glands
• Paraganglia
• Gonads and ovaries
• Hypophysis
• Pineal gland

Unpaired, the largest of the endocrine glands. Located on the side and in front of the larynx and trachea, has the form of a horseshoe. It consists of two dissimilar shares of different size: right and left, and of the unpaired thyroid isthmus, combining the two shares. The isthmus may be absent, then two shares are weakly attached one to another.

Thyroid gland produces:

• Thyroxine. Enhances the oxidation of fats, proteins, carbohydrates, increasing metabolism. Increases the excitability of the nervous system.
• Triiodothyronine. Its actions are very similar to thyroxine.
• Thyrocalcitonin. Regulate calcium metabolism by reducing it in blood and increasing in bones. Reduction of calcium levels reduces the excitability of the central nervous system.
• Calcitonin

The tissues of the thyroid gland accumulate iodine. Thyroid gland takes the form characteristic of the gland of an adult only in 5-6 years of age.

Parathyroid glands - they are small slightly flattened, oval or oblong, rarely rounded formations with a smooth shiny surface. Arranged on the rear surface of the side lobes of the thyroid gland on each side (sometimes on one). There are two upper and two lower parathyroid glands. Their number is not constant ranging from 1 to 8.

Parathyroid glands produce:

Parathyroid hormone (paratiroidin). Its action is aimed at increasing the concentration of calcium and reducing the concentration of phosphorus in the blood, due to the effect on the renal excretion of calcium (inhibits) and phosphorus (accelerates).

Parathyroid hormone together with calcitonin ensures a constant concentration of calcium ions in the blood.

Greatest activity of parathyroid is noted at an age of 4-7 years.

Thymus - an unpaired gland that is composed of right and left lobes.. It is the central organ of immunogenesis. (more detailed information about the functions of the thymus will be discussed in the topic "organs of the immune system").

It produces:
Thymosin - a hormone-like substance.

Thymosin:
• It affects the metabolism of carbohydrates and calcium (close to parathyroid hormone action of the parathyroid glands).
• It increases the number of lymphocytes.
• Strengthens the immune response.
• It participates in the process of growth and formation of the skeleton.

The largest size is reached at the age of 2 years, further to the adolescence its size varies slightly, after which begins the involution.

Pancreas belongs to mixed glands having:
• External secretion part - the exocrine portions (details will be reviewed in the digestive system).
• Internal secretion portion - endocrine portion (in the form of pancreatic islets "islets of Langerhans" in the pancreas).

Pancreatic islet cells produce matters regulating carbohydrate metabolism:
• Insuline. Increases the permeability of the plasma membrane for glucose, stimulates glycogen formation by reducing the concentration of glucose in the blood.
• Glucagon. Increases glycogen catabolism in the liver, increases glucose concentration in blood, activates gluconeogenesis, lipolysis and ketogenesis in the liver.

These are formations that are genetically related to the sympathetic nodes. Functions of paraganglia resemble the function of the adrenal medulla. Approximate location of paraganglia is represented on the right. The greatest development is reached at 1 to 1.5 years, and by 10-13 years of age, almost all paraganglia regress.

There are different:
• Male reproductive glands (testicles) that produce testosterone.
• Female reproductive glands (ovaries) that produce estradiol (estradiol increases the formation of fat and inhibits the growth of long bones), estrogen and progesterone.

They produce hormones that affect the formation of secondary sexual characteristics.

Hypophysis is often called the lower appendage of the brain. Hypophysis consists of:
• The anterior lobe (adenohypophysis).
• The posterior lobe (neurohypophysis).

Anterior lobe produces a group of tropic hormones:
• Somatotropin (STH), regulates growth and development of body.
• Prolactin.
•Adrenocorticotropic hormone (ACTH or corticotropin), stimulates the function of the adrenal cortex.
• Thyrotropic hormone (TTH, or thyrotropin), which stimulates the thyroid gland.
• Gonadotropic hormones (GTH - is - follicle stimulating gonadotropin (FSG) and luteinizing gonadotropin - LSG), that stimulate the function of sexual hormones.

Somatotropin:

It affects the growth and physical development

It stimulates the activity of osteoblasts, stimulates bone mineralization.

Increases the content of plasma glucose.

It stimulates the formation of the corpus luteum and production of progesterone in them. Production of somatotropin is regulated by the hypothalamus (somatoliberin and somatostatin).

Prolactin:

It affects the growth of the mammary glands and milk production.

Increases the reabsorption of sodium and water in the kidneys.

Production of Prolactin is regulated by the hypothalamus (prolaсtoliberin and prolaсtostatin).

Adrenocorticotropic hormone:

• It stimulates the production of glucocorticoids in the bundle area of the cortex of the adrenal glands.
• It stimulates lipolysis.
• Increases pigmentation.
• Accelerates steroidogenesis and enhances the biosynthesis of proteins and nucleic acids.

Generation of corticotropin is regulated by the hypothalamus (corticoliberin)

Thyroid-stimulating hormone:

It stimulates the production in the thyroid gland of thyroxine and triiodothyronine. Generation of thyroid-stimulating hormone is regulated by the hypothalamus (thyreoliberin)

In neurohypophysis occurs depositing of oxytocin and antidiuretic hormone (vasopressin). Hormones of the posterior lobe of the pituitary gland are the product of neurosecretion in hypothalamus and diencephalon:

Vasopressin (or ADH, or antidiuretic hormone) has an effect on the reabsorption of water (reabsorption) in the renal tubules. In large doses, it causes narrowing of arterioles.

Oxytocine It enhances smooth muscle contraction of blood vessels and the uterus, it affects the psycho-emotional state of men and women, causing more favorable disposition towards people.

Prolactin regulates the secretion of the mammary glands.

The pineal gland acts as the biological clock regulating daily and seasonal activity of the organism.

The pineal gland produces melatonin, which:
• It inhibits the function of the pituitary gland and the sex glands.
• It participates in the activities of other endocrine glands (thyroid and adrenal glands).
• Responds by many kinds of metabolism.
• It regulates blood pressure, a function of the digestive tract, the brain cell function and frequency of sleep.
• Slows the aging process.

The maximum development of the pineal gland occurs by age of 14