GLANDS (glandulae) — the cells or bodies formed by complexes of cells which under the influence of the corresponding nervous or humoral irritation or remove some substances from blood and synthesize from them the specific connections important for activity of these or those bodies and systems or concentrate and bring end products of dissimilation out of an organism.
The general functional characteristic
In each cell in the course of metabolism there are substances emitted by it to the environment. If development and allocation (secretion) of synthesizable products becomes the main or prevailing function, then cells receive the name of secretory, or ferruterous (glandulotsit). ., which of the mother substances extracted from blood (hl. obr. amino acids, ions, salts, water), specific connections synthesize and cosecrete them in surrounding or internal environment of an organism, are making. The products allocated by them to the environment of an organism are called secrets, and coming to a blood flow — incretions., the substances removing from blood which are subject to removal concentrating and allocating them without chemical processing belong to concentrating. The products allocated by concentrating. to the environment, are designated as excretes. Value of concentrating. (e.g., kidneys, stalemate., partly the lacrimal) consists in change of structure of internal environment of an organism and its clarification from end products of metabolism.
Fiziol, value of the secrets developed by glandulotsita of making., variously. One of secretory products (e.g., slime, skin fat), arriving on a body surface, promote protection against harmful effects of the environment, others affect the environment of an organism chemically, causing the reactions necessary for implementation of this or that function (e.g., the enzymes produced by glands of a digestive tract); the third are in itself feedstuffs (milk).
Among the products allocated by glandulotsita in blood and a lymph, special value belongs to hormones (see). Allocation of incretions (hormones) of a glandulotsitama in blood is called incretion (see) or an inkretion, allocation of products to the environment of an organism — external secretion (see). According to it distinguish glands of external secretion, or exocrine, and hemadens (endocrine, or incretory). Exocrine glandulotsita allocate the products synthesized by them through the top (the external, or apically directed secretion, fig. 1, a). But at the same time they, as well as any cell in general, emit through the basis in a lymph or blood some substances arising during their metabolism. This process is the internal, or basally directed secretion. In most cases the substances emitted in internal environment represent end products of dissimilation, but in certain cases together with the last the specific substances having fiziol are emitted. value for an organism. As an example of such secretory activity which is made in two directions serves the liver (fig. 1,6) which glandulotsita emit in the apical direction bile — a vneshnesekretorny product — and at the same time urea, glucose and some other synthesizable substances — in blood, i.e. carry out secretion and in the basal direction (incretion). Both types of secretion are the main for glandulotsit of a liver. If in phylogenesis fiziol, value of the products cosecreted by a cell in internal environment begins to prevail over value of the substances emitted to the environment, then the secretion apically directed gradually weakens and, at last, stops. The atrophy of output channels and transformation phylogenetic results from primary excretory gland in endocrine (fig. 1, c). Signs of such transformation clearly are traced in an embryogenesis thyroid gland (see) or an adenohypophysis — a front share hypophysis (see) which at a germ are put as. external secretion, but during further development their output channels atrophy and only allocation of the developed secretory product from glandulotsit through their basis in a blood flow remains. Other endocrine. arise from rudiments of the bodies which had in phylogenesis absolutely other functions. So, parathyroid. develop as outgrowths of an epithelium of visceral furrows. Ways of education and release of the produced substances are generally identical to all., therefore quite often the term «secret» is used more widely — for designation of the allocated product regardless of fiziol. values of the last.
As the metabolism between an organism and the environment makes the main function of epithelial fabric as boundary education (see. Epithelial fabric ), majority., in particular all exocrine, allocating a secret to the environment, have an epithelial origin, arising and developing as outgrowths of epithelial layer. From the same source some endocrine are put at a germ. (see. Hemadens ), but during further development they stand apart from epithelial layer.
Other hemadens arise as derivatives of a nervous system. Ability of neurocytes to synthetic activity is shown in development and secretion as specific substances — mediators (see), and proteinaceous products. In some specialized neurocytes ability to proteinaceous synthesis gains the increased intensity, and the developed products collect in cytoplasm in the form of specific granules just as it occurs in typical glandulotsita. Such neurocytes received the name neurosecretory, and the products developed by them — neurosecretions (see. Neurosecretion ). The last are allocated like hormones in blood with which are carried on a body, having distantny effect. Thus, secretory neurocytes are intermediate between a nervous system and endocrine. The expressed ability to secretory activity is shown in certain cases by cells of a neuroglia (e.g., an ependyma and its derivatives of which the epiphysis is formed, in particular). Some glandulotsita arise from a mesenchyma, napr, intersticial cells of gonads (see. Small egg , Ovaries ), participating in formation of sex hormones.
In addition to division on exocrine and endocrine. classify by the following signs: 1) to a structure; 2) to the chemical nature and quantity of the developed secrets; 3) to a way of allocation of a secret.
. divide on one-celled and multicellular. Among. an epithelial origin distinguish endoepithelial and ekzoepitelialny on their localization of rather epithelial layer. Endoepitelialnye. can be presented by the single glandulotsita which are mosaically scattered in the thickness of epithelial layer among its other cells (fig. 2,1) or accumulations of cells — endoepithelial ferruterous complexes. Example of one-celled. can serve scyphoid cells (see), producing slime and meeting in the epithelium covering the surface of mucous membranes (fig. 3). An example of endoepithelial ferruterous complexes are ferruterous kidneys (fig. 2, 2) and ferruterous fields (fig. 2,3); the last meet in an epithelium of a mucous membrane of a stomach (tsvetn. fig. 11).
Ekzoepitelialny multicellular glands develop in an embryogenesis as a result of the strengthened proliferation of glandulotsit of the ferruterous field (the site of epithelial layer) which caves in in the subject connecting fabric in the form of a pole («a ferruterous pole», fig. 2,4). Such its impression provides not only increase in the cosecreting surface, but also improves its blood supply. A ferruterous pole, going deep, gradually takes a form of an epithelial tyazh or a tube (fig. 2,5). The distal ends of these tubes are differentiated in trailer secretory departments (an acinus, or adenomeres) of forming., which cells begin to synthesize a secret and allocate it in a gleam of a tube. A proximal part of a tube becomes the output channel opening on the surface of the epithelial layer which gave rise given. The cells covering an output channel remain undifferentiated (fig. 2,6).
Distinguish also. simple and difficult (fig. 4). To simple. at what the output channel does not branch belong, and directly passes into trailer secretory department (e.g. stomach or stalemate. skin). If the output channel breaks up to branches of different calibers and pass only the last branchings of channels, then such into trailer secretory department. are called difficult (e.g., salivary., pancreas.). In simple. the output channel is connected with one trailer secretory department; — serves as the general bed in difficult, on Krom the secret of several or many acinus arising on the ends of the last branches of this output channel is removed. Difficult. frequent it is more simple on volume and in some cases are dismembered on shares and segments. Trailer secretory departments as in simple (e.g. greater cul-de-sac. a mucous membrane of a uterus), and in difficult. can be either a tubular, or alveolar (spherical) form. In some. tubular trailer secretory departments are very long and twist like a ball (e.g., stalemate., fig. 4,2). The branching of trailer secretory departments (fig. 4,8 and 4,5) leads to increase in the cosecreting surface. Between their folds layers of a stroma — connecting fabric with blood vessels grow.
Depending on a form of trailer secretory departments distinguish simple tubular (fig. 4,1) and simple alveolar. (fig. 4, 4). Difficult. also can be tubular (e.g., hypoglossal., fig. 4, 6) or alveolar (e.g., parotid or pancreatic., fig. 4, 7).
In difficult. at the same time both tubular, and alveolar trailer secretory departments — difficult tubular and alveolar can be found. (e.g., submaxillary salivary., fig. 4,5); and an acinus can branch, than the quantity of the cosecreting parenchyma increases even more. Tubular trailer secretory departments the branchings can connect among themselves in network, gleams between trabeculas (crossbeams) of which are filled with connecting fabric with the capillaries passing on it. Such difficult. are called mesh (fig. 4,9). Carry a liver and a front share of a hypophysis to them.
The chemical nature and quantity of the allocated secretory products
the Majority. (proteinaceous, or serous) synthesize products of the proteinaceous nature which, being easily dissolved in water, form serous liquids. Others. (mucous) produce mucins or mucoid substances. In some. secrets of lipidic or steroid character are developed (milk., large stalemate and grease. skin, bark of adrenal glands, sexual.). Secretory products of these. badly rastvorima in water
., the trailer secretory departments of a homogeneous structure developing on one secretory product and having, are called monokrinny or gomokrinny (e.g., stalemate, milk)., several various secrets producing and allocating at the same time, call heterocrine (polikrinny). In these cases trailer secretory departments are formed most often by glandulotsita of different types. Example of heterocrine. are hypoglossal and submaxillary salivary., which trailer secretory departments represent a combination of proteinaceous and mucous cells. In glands of a greater cul-de-sac trailer secretory departments consist of the main cells which are producing protein — a pepsinogen, parietal (obkladochny), emitting the active chlorides participating in education salt to - you, and additional, producing slime. Geterokriniya of a front share of a hypophysis is expressed that its trabeculas consist of chromophobic, basphilic and acidophilic adenotsit; cells of each version produce special hormones.
Way of allocation of a secret. Distinguish. with merocrine, apocrine and holocrine types of secretion. In the majority. the products developed by them are allocated in the form of water solutions which pass through a plasmolemma (a cellular cover) of glandulotsit without its damage and without disturbance of cytoplasm. Such form of allocation is called merocrine secretion (are merocrine, e.g., a pancreas., liver, salivary., endocrine.). In other cases allocation of a secret from glandulotsit is carried out by an exocytosis, i.e. extrusion (expression, pushing out) of the developed products in a type of either liquid drops, or more dense granules. These forms of allocation of a secret are transitional to apocrine type of secretion, at Krom the secret accumulates in ledges of cytoplasm, otshnurovyvayushchikhsya further from a cell. Sometimes in such way microvillis together with the granules of a secret filling them — microapocrine type of secretion separate; more often larger cytoplasmatic ledges containing a secret — macroapocrine type of secretion are squeezed out of tops of glandulotsit (and then come off). Example of macroapocrine. are large stalemate («and - glands»), milk.
If the secret is formed as a result of total transformation of a glandulotsit who deskvamirutsya exfoliated) in a gleam of trailer secretory department. (as it takes place, e.g., in grease. skin), such way of secretion receives the name of holocrine.
The nature of secretion can change depending on funkts, states Zh. Tak, in. merocrine type extrusion of granules of a secret, i.e. signs of microapocrine secretion sometimes is found. In some merocrine., especially in endocrine (bark of an adrenal gland, an adenohypophysis), separate glandulotsita completely are exposed to dystrophy; such type of secretion is called holocrine. In initial stages of functional excitement of a thyroid gland the phenomena very close to apocrine secretion are stated.
Vascularization and an innervation of glands
Since mother substances from which there is a synthesis of secretory products come to glandulotsita from blood, a condition of activity. their plentiful vascularization is. Arteries and veins, gradually branching, pass on a stroma. and, at last, capillaries in the form of more or less dense network braid trailer secretory departments. The capillary network in endocrine is especially dense., what is connected with allocation of the produced secrets (incretions) in a blood flow. For capillaries. (especially endocrine) the fenestralny type is characteristic. Existence of thinnings in an endothelial vystilka promotes the strengthened penetration of mother substances from blood in glandulotsita, and in endocrine. also to return of the produced hormones in blood and a lymph.
Efferent innervation. it is presented by sympathetic and parasympathetic fibers which, entering in., branch in it together with blood vessels, reach trailer secretory departments and, becoming amyelinic, braid them with thin diffusion network, forming terminal textures and coming into close contact with glandulotsita. In some. meet intraorganic a ganglion. The nervous impulses arriving in. on its efferent innervation, exert impact on metabolism of glandulotsit and, therefore, on biosynthesis of secretory products (trophic action), and also strengthen or weaken allocation of a secret (secretory action), mostly these effects occur jointly and at the same time (secretory and trophic action). In some. these nervous influences are shown quite clearly; in others (it is preferential in endocrine.) direct actions of a nervous factor are blocked or mask action of the humoral (hormonal) agents activating or oppressing secretory processes. At the same time nervous and humoral factors, possessing vasculomotor action, exert impact on blood supply.
Afferent innervation. it is presented by the various receptor terminations (both free, and not free) which sometimes are very difficult encapsulated [up to lamellar little bodies (Fatera — Pachini) — corpusculum lamellosum; e.g., in a pancreas.]. Such abundance and a variety of receptor devices demonstrates that in adaptation of secretory activity. to funkts, to a condition of an organism essential value belongs to the afferent nervous signals arriving from. in c. N of page. Section of afferent fibers (deafferentation.) involves disorder of activity and dystrophic changes of glandulotsit.
Cytophysiological features of glandulotsit
The ultrastructure of glandulotsit (fig. 5) is defined by their increased ability to biosynthesis and allocation of the developed products. In particular, increase in an outer surface, through to-ruyu is made absorption of mother substances and allocation of the synthesized secretory products, provided with formation of numerous folds of a plasmolemma. The side contours of glandulotsit seeming in a light microscope smooth according to a submicroscopy, are the seated ledges and vdavleiiya, and also desmosomes — the structures providing communication between cells at metaphytes (see. Desmosomes ) and the closing plates which are accustoming to drinking apical edges of the next cells. In a basal part of a glandulotsit the plasmolemma forms numerous folds, quite often branched, is deep vpyachivayushchiyesya in cytoplasm (see). The sizes of these folds increase with increase in functional activity of a glan-dulotsit. However the greatest complexity is reached by a structure of apical edge of a glandulotsit. Here (according to a submicroscopy) the plasmolemma forms microvillis — the ledges turned into a gleam of trailer secretory department. Often microvillis are located so densely that at svetooptichesky microscopy their set makes an impression of rather wide apical membrane covering a top of a glandulotsit. The quantity and the sizes of microvillis increase in process of increase of secretory activity. Sometimes microvillis otshnurovyvatsya from a glandulotsit in a gleam of trailer secretory department as it takes place at microapocrine secretion. In glandulotsita endocrine. (in particular, in thyroid.) between the bases of microvillis the phenomena of a pinocytic are often observed (absorption by cells of liquid in the form of microscopically visible drops), thanking the Crimea absorption of substances from blood glandulotsity is provided not only their diffusion through a plasmolemma, but also active swallowing. In some. [e.g., in covering (obkladochny) cells. a greater cul-de-sac] increase in an apical surface of a glandulotsit leads to emergence of the intracellular tubules which are deeply pressing in cytoplasm and densely seated by microvillis (fig. 6).
The increased synthetic activity of glandulotsit especially visually is shown by powerful development of the cytoplasmic reticulum presented concentrically by the located cracks, places extending in lacunas and tanks. As majority. produces secrets of the proteinaceous nature, their cells differ in the increased contents ribonucleic to - t and ribosomes which densely accumulate on an alpha tsitombranakh of a cytoplasmic reticulum (see. Cell ). Preferential localization of a granular cytoplasmic reticulum around a kernel and the concentration of RNA increased here lead to the fact that in the glandulotsita producing proteinaceous secrets a basal part on gistol, drugs often differs in the expressed basophilia whereas an apical part in which granules of a ready secret collect is usually painted oksifilno. As a rule, in glandulotsita the lamellar complex (Golgi's complex) is well developed, in Krom maturing of synthesizable products and registration of granules of a secret (fig. 7) comes to the end. The sizes and complexity of a lamellar complex increase parallel to increase of secretory activity. In tubules and lacunas of a cytoplasmic reticulum biosynthesis of proteinaceous secrets begins. In mucous glandulotsita the secret arises at first in the form of grains of a mutsigen which collect in a zone of a lamellar complex where, ripening, quickly bulk up, increase in volume and merge in the large drop of slime filling an apical part of a cell whereas the kernel and other organellas are pushed aside in its basal half. In the glandulotsita developing steroid secrets, the cytoplasmic reticulum is smooth and less expressed, than in the glandulotsita synthesizing proteinaceous products.
As chemical transformation of the low-molecular substances coming to a cell from the outside into more difficult connections, biosynthesis of a secret, and especially processes of allocation of the last is the cornerstone of secretory activity, demand considerable power consumption, renewed due to activity of numerous mitochondrions (see), contained in glandulotsita. Mitochondrions are scattered between tubules of a cytoplasmic reticulum, but skoplyatsya preferential in an apical part of a glandulotsit. In glands developing steroid secrets (e.g., in cells of bark of adrenal glands), biosynthesis of a secret proceeds in mitochondrions (fig. 8). Processes of allocation of a secret are connected with an ovodneniye and swelling of the cosecreting glandulotsit therefore its sizes and volume during this period considerably increase. Swelling is not limited to cytoplasm, but extends to a kernel; increase in its volume can serve as objective criterion of degree of secretory activity of a cell. In glandulotsita kernels of the roundish or slightly extended oval form prevail, but quite often they get the wrong outlines. Emergence of folds, ledges and impressions of a nuclear membrane causes increase in an interface between a kernel and cytoplasm that promotes strengthening of biosynthesis of a secret. Preservation of the nuclear and plasma relation, i.e. relation between a surface of a cellular kernel and volume of cytoplasm (see. Cell ) at strong swelling of a glandulotsit leads to a pereshnurovaniye of a kernel, and in some. [e.g., in a liver, in covering (obkladochny) cells. a greater cul-de-sac, sometimes in thyroid.] often two-and even multinuclear glandulotsita meet. The large sizes of kernels are characteristic of kernels of glandulotsit that, obviously, is connected with high intensity of synthetic activity of these cells since fiziol, value of a kernel consists in formation of ribosomalny RNA. Therefore the increase in volume of a kernel (reaching sometimes division into 2 — 3 kernels) matches strengthening of processes of biosynthesis of proteins and can serve as an indicator of this strengthening. Sometimes it is possible to observe an exit of nuclear substances through a nuclear membrane in cytoplasm, and also extrusion of a kernel.
In some. an ectodermal origin (in salivary, stalemate, milk) between the bases of glandulotsit and the basal membrane separating trailer department from intersticial connecting fabric the so-called korzinchaty cells covering trailer secretory department the shoots lie. Though korzinchaty cells are epithelial, in their shoots sokratitelny fibrilla is differentiated that gives the grounds to call these cells myoepithelial. Reduction of their shoots promotes advance of a secret from trailer secretory department to the output canal. At an inflammation, regeneration, and also in fabric cultures korzinchaty cells are rounded, in them sokratitelny fibrilla disappears, and they take a form of the low-differentiated epithelial cells capable to proliferation.
Growth and regeneration of glands
Majority. finds the expressed growth potential and regenerations. As a rule, resection of part Zh. or removal of one of steam rooms. leads to compensatory strengthening of secretory activity of the rest of a ferruterous parenchyma and to a hyperplasia of the last.
High ability of a ferruterous parenchyma to proliferation (see) causes rather frequent developing of adenomas (see. Adenoma ). In most cases proliferation of a ferruterous parenchyma happens by reproduction of the low-differentiated cells of output channels (especially their last branchings — the so-called inserted departments passing further into trailer secretory departments), is more rare — as a result of division of glandulotsit of trailer secretory department.
At a row patol, states and diseases is broken function Zh., shown, e.g., frustration sweating (see), lactations (see), secretions of a gastric juice (see. Akhiliya of a stomach ) etc. Inflammation of separate. — see. Hydradenitis , Parotitis , Pancreatitis , Sialadenitis etc. Besides, review of pathology of the majority. see in articles devoted to separate., e.g. Parotid gland (see), Pancreas (see) etc.
Bibliography: Babkin B. P. Secretory mechanism of digestive glands, L., 1960, bibliogr.; Robertis E., Novinsky V. and Saes F. Cytobiology, the lane with English, M., 1973; 3ufarov K. A., Shishov E. K. and Tashkhodzhayev P. I. Submicroscopy of bodies of the alimentary system, Tashkent, 1969, bibliogr.; Post of X. Physiology of a cell, the lane with English, M., 1975; Koshtoyants X. C. Fundamentals of comparative physiology, t. 1, M. — L., 1950, bibliogr.; Lazovsky Yu. M. The functional morphology of a stomach is normal also of pathology, M., 1947, bibliogr.; L A. Biokhimiya's enindzher, the lane with English, M., 1976; The Guide to cytology, under the editorship of A.S. Troshin, t. 2, M. — L., 1966; Functional morphology of a cell, the lane with English, M., 1963; Sh at N and to about in and E. A. Cytology and cytophysiology of secretory process, M., 1967, bibliogr.; The cell, ed. by J. Brachet a. A. E. Mir-sky, v. 5, pt 2, N. Y. — L., 1961, bibliogr.; P a 1 an at S. L. The morphology of secretion, in book: Frontiers in cytol., ed. by S. L. Palay, p. 305, New Haven, 1958, bibliogr.
B. V. Alyoshin.