EPITHELIAL FABRIC

From Big Medical Encyclopedia

EPITHELIAL FABRIC [textus epithelialis (LNH); Greek epi-on, atop + thele of pacifiers; synonym: an epithelium, epithelium] — the fabric covering a body surface and covering mucous and serous membranes of his internals (a cover epithelium), and also forming a parenchyma of the majority of glands (a ferruterous epithelium).

Epithelial fabric phylogenetic the most ancient of body tissues; it represents system of continuous layers of epithelial cells — epithelial cells. Under a layer of cells E. t. connecting fabric is located (see), ©т cover an epithelium it is accurately delimited by a basal membrane (see). Oxygen and nutrients diffuse in E. t. from capillaries through a basal membrane; in the opposite direction products of activity of cells E come to an organism. t., and in a number of bodies (e.g., in intestines, kidneys) — also the substances absorbed by epithelial cells and coming from them to a blood stream. Thus, E is functional. t. makes a whole with a basal membrane and the subject connecting fabric. Change of properties of one of components of this complex usually is followed by disturbance of structure and function of other components. E.g., at development of an epithelial malignant tumor the basal membrane collapses, and tumor cells grow into surrounding fabrics (see Cancer).

Important function E. t. protection of subjects of body tissues against mechanical, physical and chemical impacts is. Besides, through E. t. the metabolism between an organism and the environment is carried out. Part of cells E. t. it is specialized on synthesis and release (secretion) of the specific substances necessary for activity of other cells and an organism in general. The cells differentiated in this direction E. t. call secretory, or ferruterous (see Glands).

Features E. t. various bodies are connected with an origin, a structure and functions of the corresponding epithelial cells. Sources of formation definitivny E. t. the ectoderm, an entoderm and a mesoderm in this connection distinguish an ectodermal, endodermal and mesodermal epithelium serve. According to phylogenetic classification E. t., offered by N. G. Hlopin (1946), distinguish the following types of an epithelium: epidermal (e.g., skin), an enteroderma lny (e.g., intestinal), whole nefro a derma lny (e.g., renal) and ependimoglialny (e.g., covering a meninx). Reference to E. t. an epithelium of ependimoglialny type (see Neyroepitely), in particular a pigmental epithelium of a retina of an eye (see the Retina) and irises (see), and also a number of the cells of endocrine system having a neuroectodermal origin (see Hemadens), admits not all specialists. Allocation of angiodermalny type E is not also standard. t. (e.g., an endothelium of vessels) since the endothelium develops from a mesenchyma and it is genetically connected with connecting fabric. Quite often as special subspecies E. t. are considered the zachatkovy epithelium of sexual rollers developing from a mesoderm and providing development of sex cells, and also myoepithelial cells — the otrostchaty epithelial cells having ability to be reduced to-rye cover trailer departments of glands coming from a multilayer flat epithelium, napr, salivary. The called elements in the morphological and functional relations differ from other cells E. t.; in particular definitivny products of their differentiation do not form continuous layers of cells and do not bear protective function.

The epithelium, all cells to-rogo adjoin to a basal membrane, call single-layer. If at the same time cells are spread on a basal membrane and width of their basis much more surpasses height, an epithelium call single-layer flat, or squamous (fig., a). AA. t. this type plays an important role in a metabolism between Wednesdays, to-rye it divides: through a vystilka of alveoluses exchange of oxygen and carbon dioxide between air and blood, through a mesothelium of serous covers — sweating (transudation) and absorption of serous liquid is carried out. If width of the basis of epithelial cells is approximately equal to their height, an epithelium call single-layer cubic, or low-prismatic (fig., b). The epithelium of such look can also take part in bilateral transport of substances. It provides more reliable protection of the subject fabrics, than a single-layer flat epithelium

If height of epithelial cells significantly surpasses width of their basis, an epithelium call single-layer cylindrical, or high-prismatic (fig., c). The epithelium of this look usually performs difficult and quite often specialized functions; in it allocate a number of subtypes. At an identical form of epithelial cells of a high-prismatic epithelium of their kernel are located approximately at one distance from a basal membrane and on a vertical gistol. a cut seem lying in one row. Such epithelium call single-row cylindrical, or single-row high-prismatic. As a rule, it carries out, in addition to protective, also functions of absorption (e.g., in intestines) and secretions (e.g., in a stomach, in trailer departments of a number of glands). On a free surface of such epithelial cells special structures — microvillis quite often come to light (see below); in a vystilka of intestines between such cells groups or one by one the secretory elements emitting slime lie (see. Scyphoid cells).

If cells of a high-prismatic epithelium have the different form and height, then their kernels lie at different distance from a basal membrane so on a vertical gistol. a cut several rows of kernels are visible. These subspecies E. t. call a single-layer multirow high-prismatic epithelium (fig., d); it covers hl. obr. pneumatic ways. Closer to a basal membrane kernels of basal cells are located. The row, closest to a free surface, is made by kernels of ciliary cells, intermediate ranks of kernels — inserted epithelial cells and scyphoid cells allocating a mucous secret. From a basal membrane to a surface of a layer E. t. bodies only of scyphoid and ciliary cells stretch. The free distal surface of ciliary cells is covered with numerous cilia — cytoplasmatic outgrowths 5 — 15 microns long and diameter apprx. 0,2 microns. The mucous secret of scyphoid cells covers an internal vystilka of pneumatic ways. Cilia of all layer

of ciliary cells constantly move that provides advance of slime with foreign particles towards a nasopharynx and eventually removal of the last of an organism.

Thus, for all group of a single-layer epithelium the term «single-layer» belongs to cells and specifies that all of them adjoin to a basal membrane; the term «multirow» — to kernels of cells (the arrangement of kernels in several rows corresponds to distinctions in the form of epithelial cells).

The multilayer epithelium consists of several layers of cells, from to-rykh only a basal layer prilezhit to a basal membrane. Cells of a basal layer are capable to mitotic division and are a source to regeneration of overlying layers. In process of advance to a surface epithelial cells from prismatic become incorrectly many-sided and create an acanthceous layer. Epithelial cells in surface layers have a flatness; finishing the life cycle, they die off and are replaced with the flattened cells of an acanthceous layer. In a form of superficial cells such epithelium call multilayer flat neorogove-vayushchy (fig., e); it covers a cornea and a conjunctiva of an eye, covers an oral cavity and a mucous membrane of a gullet. From this type of an epithelium a multilayer flat keratosic epithelium of skin — epidermis (fig., e) differs in the fact that in process of advance to a surface and differentiations of cells of an acanthceous layer they gradually are exposed to keratinization (see), i.e. turn into the scales filled with horn substance to-rye eventually are exfoliated and replaced with new. In cytoplasm of epithelial cells granules of eleidin appear; cells with these granules (ke-ratosoma) create a granular layer over an acanthceous layer. In

Fig. Scheme of a structure of different types of epithelial fabric: and — a single-layer flat epithelium; — a single-layer cubic epithelium; in — a single-layer single-row high-prismatic epithelium; — a single-layer multirow high-prismatic (ciliary) epithelium; d — a multilayer flat neorogovevayu-shchy epithelium; e — a multilayer flat keratosic epithelium; — a transitional epithelium (at the fallen-down wall of body); z — a transitional epithelium (at the stretched wall of body). 1 — connecting fabric; 2 — a basal membrane; 3 — kernels of epithelial cells; 4 — microvillis; 5 — the closing plates (dense contacts); 6 — scyphoid cells; 7 — basal cells; 8 — inserted cells; 9 — ciliary cells; 10 — ciliary cilia; 11 — a basal layer; 12 — an acanthceous layer; 13 — a layer of flat cells; 14 — a granular layer; 15 — a brilliant layer; 16 — a corneous layer; 17 — a pigment cell *


a brilliant layer of a cell perish, and contents keratosy in mix with fat to-tami leave in intercellular spaces in a look from


nisty substance of eleidin. The outside (horn) layer consists of densely linked horn scales. The multilayer flat epithelium vypol-



the 312th epithelial coccygeal course

nyat generally protective function (see Skin).

A special form of a multilayer epithelium is the transitional epithelium of uric bodies (fig., h). It consists of three layers of cells (basal, intermediate and superficial). At stretching of a wall, napr, a bladder, cells of a surface layer are flattened, and the epithelium becomes thin, at fall of a bladder thickness of an epithelium increases, many basal cells are as if squeezed out up, and cover cells are rounded.

Blood supply and innervation E. t. are carried out from the subject connecting fabric. At the same time circulatory capillaries in a layer E. t. do not get. The exception is made by a vascular stripe of an inner ear where capillaries are localized between epithelial cells. Nerve fibrils create the free nerve terminations located between epithelial cells; in epidermis they reach a granular layer. In deep layers of epidermis nerve terminations come to light on a surface of special tactile cells of Merkel.

Boundary situation E. t. causes polarity of its cells, i.e. distinctions in a structure of parts of the epithelial cells and all layer of epithelial fabric turned to a basal membrane (a basal part) and to a free exterior surface (an apical part). These distinctions are especially noticeable in cells of different subspecies of a single-layer epithelium, napr, in enterocytes. Granular endoplasmic to a re-tic lum (see) and the majority of mitochondrions (see) are usually displaced in a basal part, and Golgi's complex, other organoids and various inclusions (see the Cell) are, as a rule, localized in an apical part. In addition to all-cellular, epithelial cells have a number of special organoids. On a free surface of cells E. t. microvillis — the finger-shaped outgrowths of cytoplasm diameter apprx. 0,1 microns participating in processes of absorption are located. Apparently, microvillis are capable to be reduced. Bunches of octynic microfilaments by diameter apprx. 6 nanometers are attached to their ends, between to-rymi the basis of a microvilli has miozinovy microfilaments. In the presence of ATP octynic microfilaments are involved in a zone of terminal network, and microvillis are shortened. Systems of microvillis 0,9 — 1,25 microns high skintight to each other form an ischerchenny border on a surface of an intestinal epithelium (see Intestines) and a brush border on a surface of epithelial cells of proximal gyrose tubules of a kidney (see). On a surface of ciliary cells of a cubic or multirow ciliary epithelium of pneumatic ways (see the Nose), uterine tubes (see), etc. cilia are located (kinotsily, undulipodiya), cores to-rykh (axoneme) are connected with basal little bodies and a filamentous cone of cytoplasm (see the Taurus basal). In an axoneme of each eyelash distinguish 9 couples (doublets) of peripheral microtubules and the central couple of single microtubules (singlets). On peripheral doublets there are «handles» from having ATF-aznoy activity of protein of a dinein. Believe that this protein plays the main role in ensuring the movements of cilia.

Mechanical strength of epithelial cells is created by a cytoskeleton — network of fibrillar structures in cytoplasm (see). At this network there are intermediate filaments thickness apprx. 10 nanometers — tonofilaments, to-rye develop in bunches — the tonofibrils reaching the maximum development in a multilayer flat epithelium. Cells E. t. communicate in layers by means of various intercellular contacts: in-terdigitation, desmosomes, dense contacts, to-rye, in particular, interfere with penetration of contents of intestines between epithelial cells, etc. Epithelial cells are connected with a basal membrane by poludesmoso-ma; tonofibrils are attached to the last.

Regeneration E. t. it is carried out by division of epithelial cells. Stem (cambial) cells are located or directly between other cells (the majority of subspecies of a single-layer epithelium), or in deepenings (crypts) pressing in connecting fabric or among the epithelial cells, closest to a basal membrane (basal cells of a multirow ciliary and transitional epithelium, a cell of basal and acanthceous layers of a multilayer flat epithelium). At small defects of a layer E. t. the next epithelial cells crawl over defect, quickly closing it; a nek-swarm the active division of surrounding cells providing a complete recovery of a layer of an epithelium begins a time later. Also the epithelial cells of sweat glands and follicles of hair located in the depth of a derma participate in closing of big defects of epidermis.

At disturbance of processes of regeneration owing to change of a trophicity, hron. inflammations, macerations emergence superficial (see the Erosion) or deep (see the Ulcer) defects of an epithelium of skin and mucous membranes is possible. Structure E. t. can deviate from norm at change of a form and function of body. E.g., at an atelectasis the flat epithelium of alveoluses becomes cubic (histologic accommodation). More permanent structural changes E. t., napr, transition of a single-layer epithelium to multilayer, call a metaplasia (see). At burns, inflammatory processes, etc. hypostasis quite often develops, there is exfoliating (desquamation) and peeling of an epithelium from a basal membrane. Hypertrophic processes are shown in development of atipichesky growths on a surface E. t. and growing tyazhy epithelial cells in the subject fabric. In epidermis disturbances of processes of keratinization in the form of keratoz (see), a hyperkeratosis (see), an ichthyosis are quite often observed (see). In bodies, the parenchyma to-rykh is presented specialized E. t., different types of dystrophy (parenchymatous or mixed), and also atipichesky regeneration with substitution E are possible. t. growths of connecting fabric (see Cirrhosis). Atrophic processes in E are characteristic of senile changes. t. and disturbances of a trophicity, to-rye in unfavorable conditions can lead to anaplastic changes (see Anaplaziya). AA. t. is a source of development of various both benign, and malignant tumors (see Tumours, Cancer).

Bibliography: Histology, under the editorship of V. G. Yeliseyev, etc., page 127, M., 1983; The X l about-p and N. G N. All-biological and experimental fundamentals of histology, D., 1946; Ham A. and Cormac D. Histology, the lane with English, t. 2, page 5, M., 1983 *

Ya. E. Hesinonim

Яндекс.Метрика