Disorder of regulation of hormone secretion and metabolism

Phylogenetically, hormones are a very ancient form of intercellular interaction. They can be produced in any organism: multicellular and protozoan, and even plant cells. In the process of evolution, clearly expressed cellular differentiation appeared, endocrine glands were formed, a system of hormonal regulation arose, the disruption of which can be one of the causes of endocrine diseases.

The synthesis and secretion of hormones are regulated by the nervous system either directly or through the release of other hormones or humoral factors. The role of the "endocrine brain", which was long attributed to the pituitary gland with its triple hormones regulating the activity of the peripheral endocrine glands, is currently assigned to a special "hypophysiotropic" region of the hypothalamus. It is here that numerous and varied nerve signals are most often transformed into humoral ones. The hypothalamus concentrates neurons that release special releasing hormones into the blood of the pituitary portal system in response to impulses or neurotransmitters coming from outside. These releasing hormones act on specific cell populations of the anterior pituitary gland, stimulating or inhibiting the release of pituitary hormones.

The hypothalamus strictly controls the pituitary-adrenal, pituitary-thyroid, and pituitary-gonadal systems. The role of hypothalamic factors is not limited to influencing the functions of the peripheral endocrine glands. It is known that corticotropin-releasing hormone activates and coordinates adaptive metabolic and behavioral reactions in stressful situations in experiments, i.e., its activity has a certain significance in behavioral reactions. Impaired secretion of this neuropeptide has been noted in depression.

Changes in the secretion of neuropeptides by the hypothalamus under certain conditions lead to pathology of the pituitary gland function. In this case, secretion of pituitary hormones with reduced biological activity is possible. A special role in the symptomatology of diseases is also played by abnormal structures of pituitary hormones. It is known that, for example, peptide fragments of somatotropin have a very specific biological effect: fragment 31-44 has high fat-mobilizing activity, 77-107 exhibits high growth activity, 44-77 leads to a decrease in glucose tolerance, causes hyperglycemia.

The most important role in the regulation of hormonal secretion is played by the feedback mechanism, which consists in the fact that with an excess of a given hormone in the blood, the secretion of its physiological stimulants is inhibited, and with its deficiency, it is enhanced. A particular manifestation of the feedback mechanism is the regulation of hormone secretion by changing the systematized parameter itself. For example, an increase in blood sugar levels increases the secretion of insulin, which reduces the sugar content. The secretion of many hormones is subject to certain rhythms (daily, seasonal, age-related) or is associated with certain physiological states (pregnancy, lactation, adaptation to new environmental conditions).

A number of endocrine glands also receive direct secretory innervation (for example, the adrenal medulla, the pineal gland). In other cases (for example, for the thyroid gland), such innervation plays a secondary role, since the main regulator of the gland's activity is the pituitary tropic hormone (in this case, thyrotropin).

Insulin secretion is subject to a complex regulation system. Its speed, like the beta-cell cell cycle, is regulated by other factors in addition to glucose: glucagon, somatostatin, pancreatic polypeptide. Recently, a new neuropeptide, galanin, has been isolated from the pancreas. It inhibits insulin secretion, inhibits the release of somatostatin while simultaneously stimulating glucagon secretion. Its secretion occurs in the nerve fibers of the pancreatic islets. Depletion of insulin secretion due to peripheral resistance and prolonged hyperinsulinemia can only occur in islets that are genetically predisposed to dysfunction.

Using the example of the description of the mechanisms of regulation of insulin secretion, one can trace the complex path of interaction of a number of factors at the level of the pancreas and their possible participation in the pathogenesis of disorders.

Humoral factors are also an important link in the pathogenesis of many endocrine diseases. Thus, the growth and development of a child depend not only on the secretion of growth hormone by the pituitary gland, but also on the state of intermediary mechanisms - in particular, on the level of insulin-like growth factor (somatomedin C) in the blood. Somatomedins are biologically active polypeptides produced in the liver and kidneys in response to stimulation of somatotropic hormone (STH) and have a growth and insulin-like effect. They are the most powerful stimulators of cartilage growth, actively react with receptors and displace insulin from the surface of cartilage cells, are similar in structure to proinsulin, and differ qualitatively and quantitatively from the action of insulin. The content of somatomedins in plasma decreases under conditions of starvation and with a subcaloric, protein-poor diet.

Depending on their hydro- or lipophilicity, hormones circulate in the blood either free or bound to specific proteins. Binding to proteins slows down the metabolism and inactivation of hormones.

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