HEMADENS (synonym: closed glands, incretory glands) — the bodies which are producing specialized in process of evolution and emitting directly in internal environment of an organism physiologically active agents (hormones). A concept about incretion (see) and about hemadens K. Bernard entered (1855).
Incretion is inherent to all cells of a metaphyte since each of them allocates products of metabolism in an intercellular lymph, a lymph or blood. Some of them have the exciting or oppressing effect on functions of an organism, i.e. possess fiziol, activity. If formation of physiologically active agents is main or one of the main functions of cells, then the bodies consisting of such cells are called endocrine.
At vertebrata (and the person) to. the century of page producing only hormones (see), belong hypophysis (see), thyroid gland (see), epithelial bodies (see) and adrenal glands (see). Confirmation of endocrine value is received pinus (see). Other group is made by the bodies combining production of hormones with other functions — pancreas (see) small egg (see), ovaries (see) and placenta (see). Incretory activity is inherent also a nek-eye to the bodies which are usually not carried to endocrine system — to sialadens, to bodies went. - kish. a path, to kidneys, perhaps a spleen, and also a thymus, edges, being the central body of an immunogenesis, produces also some active agents influencing development of lymphoid cells (see. Thymus ).
Features of a structure and regulation of function Zh. century of page depend on their development and specialization in the course of phylogenesis. Some closed glands — an adenohypophysis (front and average shares of a hypophysis), a thyroid gland, epithelial (parathyroid) bodies — are put in an embryogenesis as glands of external secretion, but at further development release of the cosecreted substances in blood or a lymph through the basal ends of adenotsit (ferruterous cells) becomes the dominating process in this connection output channels are reduced (see. Glands ). Other glands are put and form at once as. century of page.
Majority. century with, consists of several fabric components arising from different embryonal rudiments and entering a uniform functional and structural complex; e.g., a part of a hypophysis flutters from an epithelium of an oral cavity, and another — as an outgrowth of the distal end of a funnel of the third ventricle of a brain, and the created hypophysis, thus, consists of an epithelial adenohypophysis and a glial back share. Thyroid and epithelial bodies come from different embryonal rudiments, function and are regulated absolutely separately, but topographical are integrated and receive the general blood supply and an innervation. In adrenal glands two independent glands — cortical, coming from a tselodermalny epithelium, and brain (medullary), being a modified sympathetic ganglion are integrated. In a pancreas endocrine pancreatic islands are located between an exocrine acinus. In testicles and ovaries the generative (gametogenny) and follicular epithelium, and also intersticial cells of a mesenchymal origin are combined. In development and functioning of a placenta interaction of covers of a germ and endometria of mother is shown.
Microscopically the uniform principle of a structure is found. century of page.
Hormone-producing cells closely contact to the circulatory capillaries having a special structure (fenestrirovanny capillaries); plentiful blood supply is characteristic. century of page.
Majority. century of page produces several hormones, various on chemical structure and fiziol, to effect. So, the front share of a hypophysis cosecretes not less than six various hormones, an average share of a hypophysis — two hormones, the thyroid gland of mammals produces three hormones etc. In detail about hormones of everyone. century of page, them fiziol, the action and diseases connected with dysfunction — see the table.
On features of regulation of function Zh. it is possible to divide century of page into four groups. The adenohypophysis, a thyroid gland, testicles and ovaries (gonads), and also puchkovy and mesh zones of bark of adrenal glands concern to the first group. In this group the front share of a hypophysis holds central position since produces the triple (krinotropny) hormones regulating activity of other glands of this group.
To the second group Zh. century of the page (which are not in direct dependence on a hypophysis) belong epithelial bodies, pancreatic islands and a glomerular zone of bark of adrenal glands, and also a thymus. Regulation of function of these glands is defined by direct influence on them of those effects which arise in an organism as a result of effect of their hormones. So, parathyroid hormone increases the level of calcium in blood, but excess of calcium in turn oppresses secretory activity of epithelial bodies. Functional activity of pancreatic islands correlates with the level of a glycemia: the hyperglycemia stimulates secretion of insulin, and insulin lowers a sugar content in blood. Functional activity of this group of glands allows to characterize conditionally them as self-regulating. century of page. Switching off of glands of this group leads to death whereas removal of hypophysical dependent glands and even a hypophysis is compatible to preservation of life, though is followed by heavy disorders of many functions of an organism.
The third group of incretory educations is made by hormone-producing glands or single cells of a nervous origin; their activity does not depend on a front share of a hypophysis. Emergence. for century of page from nervous tissue it is caused by the fact that nervous cells in itself are capable to develop and emit physiologically active agents — the mediators realizing momentum transfer in synapses from neuron on an effector or from one neuron on another. The regulating influence of nervous impulses is carried out gumoralno, as well as influence of hormones that demonstrates unity of nervous and hormonal systems of an organism because fiziol, value of these systems consists in regulation of separate functions of an organism and their coordination. In some nervous cells along with mediators the secretory substances which are coming to light in cytoplasm of perikaryon in the form of granules are produced; such cells received the name of neurosecretory (fig.), and the substances produced by them — neurosecretions (see. Neurosecretion ). Sharrer (E. Scharrer, 1952) established that neurosecretory cells, combining nervous and endocrine functions, perceive the impulses arriving to them from other parts of the nervous system and transfer them further in the form of the neurosecretions postponed with a blood flow. If existence of the shoots providing the directed transfer of nervous impulse is characteristic of neurons, then neurosecretory cells can not have shoots; e.g., chromaffin cells of a brain part of adrenal glands and paragangliyev and parafollicular, or K-cells, thyroid gland.
At vertebrata neurosecretory cells concentrate in hypothalamus (see); they cosecrete group of the hormones (rileasing-hormones, or rileasing-factors) activating or oppressing secretion of adenogipofizarny hormones (see. Hypothalamic neurohormones ), and also vasopressin (see) and oxytocin (see). In went. - kish. a path the neuroblasts migrating in the course of an embryogenesis join in a mucous membrane and will be transformed to the argyrophil cells which are presumably producing gastrin — specific hormone of a stomach. In a mucous membrane of a stomach and intestines neuroblasts give rise to enterokhromaffinny cells (see. Argentaffin cells ), though functional value of these cells is not quite established, their incretory activity is obvious. It is not excluded that enterokhromaffinny cells of a stomach produce along with gastrin secretin, and enterokhromaffinny cells of intestines (Kulchitsky's cell) — secretin. There is a point of view that also beta cells of pancreatic islands belong to group of neuroendocrinal cells alpha.
Bodies of endocrine system of a neuroglial origin can be carried to the fourth group, including. pinus (see). The epiphysis clearly oppresses secretion of gonadotropic anterior pituitary hormones and, therefore, reduces hormonal and reproductive functions of gonads.
The ependyma of a bottom of the third ventricle of a brain and its funnel gives rise to a back share of a hypophysis (neurohypophysis) and an intermediate part (a medial eminention). The parenchyma of a back share of a hypophysis is made by a neuroglia. The back share does not produce hormones, and is the subsidiary neyrogemalny body of gipotalamoneyrogipofizarny system providing accumulation and allocation in blood of vasopressin and oxytocin developed by neurosecretory cells of front department of a hypothalamus; the same role in gipotalamoadenogipofizarny system is played by a median eminence. On the capillaries located in a median eminence axons of small neurosecretory cells of a mediobazalny hypothalamus come to an end; here Hypothalamic neurohormones are emitted in the blood bringing them to a parenchyma of a front share of a hypophysis. The median eminence of a hypothalamus and a back share of a hypophysis belong to ependimny tsirkumventrikulyarny bodies, to the Crimea also subkomissuralny body, subfornikalny body, vascular bodies of a terminal plate and areae postremae belong (at animals).
Funkts, interdependence of the separate bodies and educations producing hormones and regulating a homeostasis of an organism, defines association Zh. century of page in uniform endocrine system (tsvetn. fig. 11); the division of components of this system for four groups can plan classification of endocrine organs.
I. Group of an adenohypophysis and peripheral closed glands, dependent on it: adenohypophysis, thyroid gland, small egg, ovary, bark of adrenal glands (puchkovy and mesh zones).
II. Group of the peripheral closed glands which are not depending on a front share of a hypophysis: epithelial bodies, thymus, bark of adrenal glands (glomerular zone), pancreatic islands.
III. Group of endocrine organs of a nervous origin (neuroendocrinal). 1. Neuroendocrinal cells with shoots: a) large neurosecretory cells (so-called gomoripolozhitelny) of nadzritelny and okolozheludochkovy kernels of front department of a hypothalamus and b) small neurosecretory cells of an adenogipofizotropny zone of a mediobazalny hypothalamus of departments. 2. The neuroendocrinal cells deprived of shoots: chromaffin cells of a brain part of adrenal glands and paragangliyev; parafollicular, or K-cells, thyroid gland; argyrophil cells of a stomach and intestines; enterokhromaffinny cells of a stomach and intestines.
IV. Group of endocrine organs of a neuroglial origin: a) pinus; b) tsirkumventrikulyarny bodies (subkomissuralny, subfornikalny, vascular body of a terminal plate, vascular body of areae postremae); c) neyrogemalny bodies (back share of a hypophysis, median eminence).
In neuroendocrinal system the regulating center is the hypothalamus. The regulating impulses sent them reach peripheral effectors or through a hypophysis (a humoral way), or, passing a hypophysis, on the descending nerve pathways. Essentially the same dual mechanisms provide feed-backs, i.e. influence of peripheral. century of page on a hypothalamus (see. Neurohumoral regulation ).
Preservation of hormonal balance in an organism means that degree of secretory activity of a closed gland is inversely proportional concentration of its hormone in blood. Preservation of hormonal balance can happen at the different levels of regulation. As an initial and at the same time most general form of regulation it is necessary to recognize direct effect of hormones (or those shifts in an organism which they cause) on gland producing them. This form of interaction can be shown as well at hypophysical dependent glands. Balance between concentration of hormones in blood and degree of functional activity of dependent glands, becoming isolated at the level of a front share of a hypophysis and a hypothalamus, is defined by relationship between these dependent glands and a front share of a hypophysis. If tropny hormone activates a peripheral closed gland (iron effector, or gland target), then hormone (hormones) of the last oppresses products and secretion of the corresponding triple hormone of a hypophysis, i.e. relationship between peripheral. century the page and a front share of a hypophysis have character of negative feed-backs. E.g., the lowering of the level of thyroid hormones (caused by a thyroidectomy or administration of thyreostatic substances) leads to significant increase in products and secretion of Thyrotropinum a front share of a hypophysis. In a similar way castration causes clear strengthening of follicle-stimulating function of a hypophysis, and insufficiency of adrenal hormones — activation of its adrenocorticotropic function.
Generalizing these ratios, M. M. Zavadovsky (1933) formulated the principle a plus-minus of interaction, including it the universal mechanism defining maintenance of hormonal balance. Actually this principle reflects only one of private forms of balance between a closed gland and the effect caused by its hormone. The return (afferent) influences proceeding from peripheral gland effector can affect not directly a front share of a hypophysis, and through a hypothalamus, oppressing formation of the hypothalamic neurohormones activating the corresponding functions of a front share of a hypophysis. At the same time hormones of peripheral glands can have effect and on the highest departments of a brain from where information is transmitted through a hypothalamus and an adenohypophysis to the closed gland producing these hormones.
Relationship between a hypothalamus and an adenohypophysis also, apparently, has character of negative feed-backs (so-called small feed-backs).
In the general system of regulatory interactions. century of page are outlined two circles — small, providing functional balance between a hypothalamus and an adenohypophysis, and a big circle — relationship between gipotalamo-pituitary system (see) and peripheral. century of page
See also Endocrine system .
Table. KLINIKO-FIZIOLOGIChESKAYa CHARACTERISTIC of HEMADENS
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B. V. Alyoshin; authors of the tab. P. S. Zavadsky, A. G. Mazowiecki.