Disorder of the regulation of hormone secretion and metabolism
Last reviewed: 23.04.2024
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Hormones are phylogenetically 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, a distinctly differentiated cellular differentiation emerged, glands of internal secretion formed, a system of hormonal regulation appeared, the violation of which can be one of the causes of endocrine diseases.
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 for a long time was attributed to the pituitary gland with its triple hormones regulating the activity of the peripheral endocrine glands, is currently assigned to a special "hypophysiotropic" area of the hypothalamus. It is here that numerous and diverse nerve signals are most often transformed into humoral signals. In the hypothalamus, neurons are concentrated which, in response to impulses or neurotransmitters coming from outside, release special releasing hormones into the blood of the portal system of the pituitary gland. These releasing hormones act on specific cell populations of the anterior pituitary gland, stimulating or inhibiting the release of pituitary hormones.
Under the strict control of the hypothalamus, the pituitary-adrenal, pituitary-thyroid and pituitary-gonadal systems function. The role of hypothalamic factors is not limited only to the influence on the functions of the peripheral glands of internal secretion. It is known that corticotropin-releasing hormone in an experiment activates and coordinates adaptive metabolic and behavioral reactions under stressful situations, that is, its activity has definite significance in behavioral reactions. Violation of the secretion of this neuropeptide is noted in depression.
Change in the secretion of the hypothalamus neuropeptides under certain conditions leads to a pathology of the pituitary gland function. In this case, the secretion of pituitary hormones with reduced biological activity is possible. Anomalous structures of pituitary hormones play a special role in the symptomatology of diseases. It is known that, for example, peptide fragments of somatotropin have a quite definite biological effect: fragment 31-44 has a high fat-mobilizing activity, 77-107 exhibits great 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 the excessive content of this hormone in the blood inhibits the secretion of its physiological stimulants, and if it is deficient, it increases. A particular manifestation of the feedback mechanism is the regulation of the release of the hormone by a change in the systematized parameter itself. For example, increasing blood sugar levels increases insulin secretion, which reduces the sugar content. The allocation of many hormones obeys certain rhythms (daily, seasonal, age) or is associated with certain physiological conditions (pregnancy, lactation, adaptation to new environmental conditions).
A number of endocrine glands receives direct secretory innervation (for example, adrenal medulla, epiphysis). In other cases (for example, for the thyroid gland), this innervation plays a secondary role, since the main regulator of the gland activity is the tropic hormone of the pituitary (in this case, thyrotropin).
Complicated system of regulation obeys the secretion of insulin. Its speed, like the cell cycle of beta cells, in addition to glucose, is regulated by other factors: glucagon, somatostatin, pancreatic polypeptide. Recently, a new neuropeptide-galanin has been isolated from the pancreas, which inhibits the secretion of insulin, inhibits the release of somatostatin while stimulating glucagon secretion. Its release occurs in the nerve fibers of the islets of the pancreas. Depletion of insulin secretion due to peripheral resistance and prolonged hyperinsulinemia can occur only in islets genetically predisposed to impairment of function.
Using the example of the mechanisms of regulation of insulin secretion, it is possible to 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. So, the growth and development of a child depends not only on the pituitary gland secretion of growth hormone, but also on the state of the mediator mechanisms - in particular, the blood level of the insulin-like growth factor (somatomedin C). Somatomedins are biologically active polypeptides produced in the liver and kidneys in response to stimulation of growth hormone (STH) and possessing growth and insulin-like action. They are the most powerful stimulators of cartilage growth, actively react with receptors and displace insulin from the surface of cartilaginous cells, are close in structure to proinsulin, qualitatively and quantitatively differ from insulin action. The content of somatomedins in plasma decreases under starvation conditions and with a subcaloric, protein-poor diet.
Depending on its hydro- or lipophilicity, the hormones circulate in the blood either in the free or in the form associated with specific proteins. The association with proteins slows the metabolism and inactivation of hormones.
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