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ENDOTHELIUM [endothelium (LNH); Greek endon inside + thele of pacifiers] — a cellular vystilka of an inner surface of circulatory, absorbent vessels and an endocardium.

AA. it is identical to a flat epithelium, but develops from a mesenchyma (see) and genetically has no relation to epithelial fabric (see). The term «endothelium» entered W. His Senior in 1865.

Structure E. substantially causes features of a hemodynamics (see). Cells E. have diameter of 20 — 40 microns depending on features of a structure of blood vessels (see), thickness of 0,1 — 1,0 microns; in a zone of a kernel thickness of cells increases by 4 — 5 times. The kernel is located is central, it more or less large, a round or oval form. Edges of cells rather densely are closed or connect to the help of gear bonds up to manual couplings (interdigitation) or crawl at each other like scales. According to it cells E., connecting, can form a solid line or fenestrated mezhendo-telialny cracks. Width of mezhendo-telialny cracks varies from 100 to 200 nanometers. In cytoplasm of cells E. there is a set of organellas, microfilaments and microtubules making a stroma E., and also set of bubbles, or vesicles, to dia. 600 — 700 nanometers, from to-rykh one open on an outer (basal) surface, others — on internal (lyuminalny), turned into a gleam of a vessel, and the third freely lie in cytoplasm, without contacting plasma membranes. At merge of vesicles trans-cellular tubules are formed. At considerable thinning of a layer of cytoplasm in cells there are through holes, or a true time (e.g., in E. capillaries of renal balls). The time closed by a thin plasma membrane (to 40 nanometers), or a diaphragm, calls fe-nestram. They meet in circulatory capillaries of a kidney, closed glands, marrow, intestinal fibers (see Capillaries). Fenestra it is possible to find also in mouths of plazmalemmny vesicles on a basal surface of cells E. (the blinded vesicles).

On an inner surface E. there are cellular outgrowths (microvillis), the differentiated microzones differing in a structure, concentration of anions, density are mosaically distributed. Outer surface E. borders on a basal membrane. Components of a basal membrane in the form of glycoproteins get into mezhendotelial-ny cracks. In vessels of average and large caliber under E. the subendothelial layer which is a component of an internal cover of a vascular wall lies.

Specific features E. vessels of various type and different bodies cause a variety of its functions. AA. provides exchange processes between blood and fabrics by transfer of substances by means of vesicles, and also through a time, fenestra and mezhendotelial-ny cracks (see Microcirculation, Mikrotsirkulyation), and low-molecular weight compounds and ions are transferred on intercellular intervals, and macromolecules — by means of vesicles. In an endothelium collagen, DNA, actin, prostacyclin, fibrinolysin, plasminogen and other substances are formed. AA. has antigenic activity and ability to phagocytosis (see); influences rheological properties of blood (see Blood, the Rheology); it is characterized by well-marked ability to proliferation. Changes of a form, an arrangement of endothelial cells or local changes of surface-bound electric charge (especially in fe-nestrirovanny capillaries, e.g., renal balls) under the influence of external or internal patol. factors lead to disturbance of their permeability (see)*. The endothelium can become a source of development of an angioendotelioma (see).

Bibliography: Zavarzin A. A. Log huts

ranny works, t. 1 — 4, M. — JI., 1950 — ■ 1953; Karaganov Ya. L., To e r d-varenko both N. V. and Levin V. of N, Microangiology, Chisinau, 1982; Kupriyanov V. V. Ways of microcirculation, Chisinau, 1969; The X l about p and N. G N. All-biological and experimental fundamentals of histology, L., 1946; Sh and x l and-mov V. A. Capillaries, M., 1971; Shchelkunov S. I. Philosophy of a cellular differentiation, M., 1977; And 1 t-s with h u 1 R. Endothelium, its development, morphology, function, and pathology, N. Y., 1954; Freudenberg N., Riese K. - H. a. Freudenberg M. A. The vascular endothelial system, Stuttgart — N. Y., 1983; Vascular endothelium and basement membranes, ed. by B. M. Altura, Basel — N. Y., 1980.

V. V. Kupriyanov.