The main role in the functioning of the endocrine system is played by the hypothalamus, pituitary gland and adrenal glands. These glands regulate the course of processes that ensure the interaction of all parts of our body. The highest subcortical center of endocrine regulation is the hypothalamus – the medulla oblongata. It releases neurohormones that stimulate the pituitary gland.
The pituitary gland is an endocrine gland that regulates the activity of many other endocrine glands (and, accordingly, human organs).
This gland is the size of a pea (the mass of the pituitary gland in an adult is 0.6–1.1 g), located at the base of the brain, and consists of three lobes (anterior, posterior, and middle).
The anterior pituitary gland secretes hormones (tropic hormones) that affect the growth and function of other endocrine glands. These hormones regulate functions:
- thyroid gland (thyroid-stimulating hormone),
- genital glands (gonadotropic hormone),
- adrenal cortex (adrenocorticotropic hormone – ACTH).
Another of the hormones of the anterior pituitary gland – growth hormone, or somatotropic hormone – regulates the growth of bones in length, accelerates metabolism. With its lack, the growth of the child slows down, dwarfism develops (the proportions of the body and the mental development of a person are not disturbed).
An increase in the content of growth hormone in a child’s body causes its increased growth and leads to gigantism.
When an excess amount of growth hormones is released into the bloodstream in an adult, when bone growth is complete, acromegaly disease develops. In such patients, the bones of the fingers, feet, and the facial part of the skull are enlarged. At the same time, the nose and chin grow vigorously, the tongue, the volume of the heart and other organs increase. The vocal cords thicken and the voice becomes rough.
The pituitary gland secretes hormones that stimulate the growth and maturation of germ cells, the formation and secretion of milk by the mammary glands, and also affect the water-salt metabolism in the body.
The secretion of pituitary hormones into the blood is regulated according to the principle of feedback (self-regulation): a decrease in the content of a certain hormone in the blood causes the pituitary gland to release the corresponding hormone, which increases the activity of the gland.
The posterior lobe of the pituitary gland releases two hormones into the blood:
- the hormone vasopressin enhances the process of reabsorption, i.e., the reabsorption of water in the renal tubules. With a lack of this hormone, a lot of urine is formed and diabetes insipidus develops.
- The hormone oxytocin acts on smooth muscle and causes it to contract. This hormone is produced during childbirth; it stimulates the contraction of the walls of the uterus and the release of milk from the mammary glands in lactating women.
In the middle lobe of the pituitary gland, a melanotropic hormone is produced, which affects the formation of melanin pigment in skin cells and determines its color.
Pineal gland (pineal gland) – refers to the brain and regulates the biological rhythms of the body (daily, seasonal, etc.). It produces a hormone that inhibits premature puberty. The release of the hormone depends on the light.
The adrenal glands are located at the upper poles of the kidneys and look like flattened pyramids.
Each adrenal gland consists of the outer, cortical, and inner, medullary layers.
The adrenal cortex produces more than 40 hormones that affect metabolism, regulate mineral and water metabolism. The adrenal glands also produce sex hormones.
The adrenal medulla produces the hormone adrenaline (when the body is exposed to strong stressful stimuli, such as fear).
Adrenaline increases the excitability of the nervous system, increases the heart rate, affects the vascular lumen (dilates the vessels of the heart), increases blood flow in the liver, muscles, brain, and reduces muscle fatigue.
The adrenal glands also produce the hormone norepinephrine, which plays the role of a neurotransmitter in synapses. Norepinephrine increases arteriole tone and blood pressure.
Thymus (thymus gland)
The thymus (thymus gland) is located behind the sternum and is developed in newborns. Its hormones affect immunity, regulate the function of other endocrine glands: inhibit the activity of the thyroid gland, delay the body’s puberty.
In adults, the thymus atrophies. In this gland, differentiation and multiplication of cells – precursors of T-lymphocytes occurs, the hormone thymosin regulates carbohydrate metabolism and calcium metabolism, affects the regulation of neuromuscular transmission.