Hormones of the hypothalamus

The hypothalamus is defined as a hypothalamus, which occupies part of the intermediate brain, located downstream from the thalamus under the hypothalamic furrow, and is a cluster of nerve cells with numerous afferent and efferent connections. Hypothalamus is the highest vegetative center, coordinating the functions of various internal systems, adapting them to the holistic activity of the organism. It is essential in maintaining the optimal level of metabolism (protein, carbohydrate, fat, water and mineral) and energy, in regulating the body's temperature balance, digestive, cardiovascular, excretory, respiratory and endocrine systems. Under the control of the hypothalamus there are such endocrine glands as the pituitary gland, the thyroid gland, the sex glands, the adrenal glands, the pancreas.

Regulation of tropic functions of the pituitary gland is carried out by isolating the hypothalamic neurohormones entering the gland through the portal system of blood vessels. Between the hypothalamus and the pituitary, there is an inverse relationship, through which their secretory functions are regulated. This connection is usually called short, unlike the long, connecting "target" gland and hypothalamus or pituitary gland, and ultrashort feedback, which closes in the same structure in which the hormone is released. The process of secretion of tropic hormones of the pituitary gland is controlled both by peripheral hormones and by hypothalamic releasing hormones. In the hypothalamus seven hypothalamic neurohormones, activating, and three - inhibiting the release of tropic hormones of the pituitary gland are found. Classification of hypothalamic neurohormones is based on their ability to stimulate or inhibit the release of the corresponding hormone of the pituitary gland. The first group includes corticoliberin - the releasing hormone ACTH, or corticotropic (CRH); Thyreoliberin - thyrotropin-releasing hormone (TRH); lylyberin - releasing hormone luteinizing hormone (LH-RG); folleberin - releasing hormone follicle-stimulating hormone (FSH-RG); somatoliberin - somatotropin-releasing hormone (SRH); prolactoliberin-prolactin-releasing hormone (PWG); melanoliberin - releasing hormone melanocyte-stimulating hormone (IGR); to the second - prolaktostatin - prolaktinin-gibiruyuschy hormone (UIF); melanostatin - inhibiting hormone melanocyte-stimulating hormone (MYTH); Somatostatin - a somatotropin-inhibiting factor (CIF). Hypothalamic neurohormones should also include vasopressin (VP) and oxytocin, produced by nerve cells of large-cell hypothalamus nuclei, which are transported along their own axons to the posterior lobe of the pituitary gland. All hypothalamic neurohormones are substances of a peptide nature. Studies of the chemical structure of neurohormones, begun more than 25 years ago, established the structure of only five hormones of this group of peptides: TRG, LH-RG, CIF, AWG and KRG. These compounds consist respectively of 3, 10, 14, 44, 41 amino acids. The chemical nature of the remaining hypothalamic releasing hormones is not fully established. The content of neuro-hormones in the hypothalamus is very insignificant and is expressed in nanograms. Synthesis of five of these neuropeptides in large quantities allowed us to work out radioimmunological methods for their determination and clarify their localization in the hypothalamic nuclei. Data from recent years indicate a wide spread of neurohormones outside the hypothalamus, in other structures of the central nervous system, as well as in the gastrointestinal tract. There is every reason to believe that these hypothalamic neurohormones perform endocrine and neurotransmitter or neuromodulatory functions, being one of the components of physiologically active substances that determine a number of systemic reactions, such as sleep, memory, sexual behavior, and others.

Hypothalamic neurohormones are synthesized in the pericarions of the neurons of the small-cell structures of the hypothalamus, from where they enter axons into the nerve endings, where they accumulate in separate synaptic vesicles. It is assumed that perikaryons store a prohormone with a higher relative molecular mass than the true hormone released into the synaptic cleft. It should be noted some discreteness of the localization of synthesis sites in the hypothalamus of lylyberyrin (anterior hypothalamus) and the diffusivity of tiroliberin and somatostatin. For example, the content of thyreoliberin in the hypothalamus is only 25% of its total content in the central nervous system. Discreteness of the localization of neurohormones determines the involvement of this or that region of the hypothalamus in the regulation of a certain trophic function of the pituitary gland. It is believed that the anterior part of the hypothalamus takes a direct part in the regulation of gonadotropin release. Most researchers consider the center of regulation of the thyroid function of the pituitary gland to be located in the antero-basal part of the hypothalamus, below the parenchymal nucleus, extending from the supernumerary nuclei in front to the arcuate nuclei posteriorly. Localization of areas that selectively control the adrenocorticotropic function of the pituitary gland has not been adequately studied. A number of scientists associate the regulation of ACTH release with the posterior region of the hypothalamus. The localization of hypothalamic regions involved in the regulation of the secretion of the remaining tropic hormones in the pituitary gland remains unclear. It should be noted that the maximum concentration of all known hypothalamic neurohormones is found in the middle elevation, that is, at the final stage of their entry into the portal system. Functional isolation and demarcation of hypothalamic zones by their participation in the control of tropic functions of the pituitary gland can not be carried out sufficiently clearly. Numerous studies have shown that the anterior region of the hypothalamus has a stimulating effect on sexual development, and the rear region is inhibitory. In patients with pathology of the hypothalamic region there is a violation of the functions of the reproductive system - sexual weakness, violation of the menstrual cycle. There are many cases of accelerated puberty as a result of excessive stimulation of the tumor region of the gray hillock. In adiposogenital syndrome, associated with a lesion of the tuberal region of the hypothalamus, there are also disorders of the sexual function. Reduction or even complete loss of smell in hypogenitalism is also associated with a decrease in the content of lylyberyn in olfactory bulbs.

Hypothalamus is involved in the regulation of carbohydrate metabolism - damage to its posterior parts causes hyperglycemia. In some cases, with changes in the hypothalamus, obesity, cachexia, is observed. It develops usually when the upper medial nucleus and the gray throat area of the hypothalamus are affected. The role of the surveillance and peri-oedematous nuclei in the mechanism of the development of diabetes insipidus is shown.

The close relationship of the hypothalamus with other structures of the central nervous system determines its participation in many other physiological processes of the body's vital activity - thermoregulation, digestion and regulation of blood pressure, alternation of sleep and wakefulness. He has the main role in the formation of the main instincts of the body - motivation. This is based on the ability of hypothalamic neurons to respond specifically to changes in blood pH, the voltage of carbon dioxide and oxygen, the content of ions, especially potassium and sodium. In other words, hypothalamus cells function as receptors that perceive a change in homeostasis, and have the ability to transform humoral changes in the internal environment into the nervous process. The excitation that appears in the cells of the hypothalamus extends to neighboring structures of the brain. This leads to motivational excitement, accompanied by a qualitative biological originality of behavior.

Hypothalamic neurohormones are highly active physiological compounds occupying a leading place in the system of feedbacks between the hypothalamus, pituitary gland and target glands. The physiological effect of neurohormones is reduced to an increase or decrease in the concentration of the corresponding tropic hormones in the blood. Attention should be paid to the lack of specific specificity in hypothalamic neurohormones, which is very important for medical practice.

[1], [2], [3]