CAPILLARIES

From Big Medical Encyclopedia

CAPILLARIES (Latin. capillaris hair) — the most thin-walled vessels of a microcirculator bed, on the Crimea moves blood and a lymph. Distinguish circulatory and lymphatic capillaries (fig. 1).

Fig. 1. Microcirculator bed of a fibrous renal capsule: circulatory (1) and lymphatic (2) capillaries. Microscopic drug, impregnirovanny silver nitrite; X 120.

Ontogenesis

Cellular elements of a wall of capillaries and a blood cell have a uniform source of development and arise in an embryogenesis from a mesenchyma. However general patterns of development circulatory and limf. To. in an embryogenesis are studied not enough. Throughout ontogenesis circulatory To. constantly change that is expressed in a zapustevaniye and an obliteration of one To. and new growth of others. Emergence new circulatory To. occurs by protrusion («budding») of a wall earlier formed To. This process happens during the strengthening of function of this or that body, and also at revascularization of bodies. Process of protrusion is followed by division of endothelial cells and increase in the sizes of «a kidney of growth». At merge growing To. to a wall of the preexisting vessel there is a perforation of the endothelial cell located on a top of «a kidney of growth» and connection of gleams of both vessels. The endothelium of the capillaries which are formed by budding has no interendothelial contacts and is called «seamless». By an old age a structure circulatory To. significantly changes that is shown by reduction of number and the sizes of capillary loops, increase in distance between them, emergence sharply gyrose To., in which narrowings of a gleam alternate with the expressed expansions (Senile varicosity, according to D. A. Zhdanov), and also a considerable thickening of basal membranes, dystrophy of endothelial cells and consolidation of the connecting fabric surrounding To. This reorganization causes decrease in functions of gas exchange and food of fabrics.

Circulatory capillaries are available in all bodies and fabrics, they are continuation of arterioles, precapillary arterioles (precapillaries) or, more often, lateral branches of the last. Separate To., combining among themselves, pass into post-capillary venules (post-capillaries). The last, merging with each other, give rise to the collective venules which are taking out blood in larger venules. An exception of this rule at the person and mammals are sinusoidny (with a wide gleam) To. a liver, located between the bringing and taking out venous microvessels, and glomerular To. renal little bodies, located on the course of the bringing and taking out arterioles.

Circulatory To. for the first time found in lungs of a frog of M. Malpigi in 1661; 100 years later L. Spallanzani found To. and at hematothermal animals. Opening of capillary ways of transport of blood completed creation of the evidence-based ideas of a loop system of blood circulation put by U. Garvey. In Russia the beginning to systematic studying To. put N. A. Hrzhonshchevsky's researches (1866), A. E. Golubeva (1868), A. I. Ivanov (1868), M. D. Lavdovspy (1870). An essential contribution to studying of anatomy and physiology To. brought dates. physiologist A. Krog (1927). However the greatest progress in studying of the structurally functional organization K. were reached in the second half of 20 century that was promoted by the numerous researches executed in the USSR by D. A. Zhdanov with sotr. in 1940 — 1970, V. V. Kupriyanov with sotr. in 1958 — 1977, A. M. Chernukh with sotr. in 1966 — 1977, G. I. Mchedlishvili with sotr. in 1958 — 1977, etc., and abroad — Len-disom (E. M of Landis) in 1926 — 1977, Tsveyfakh (V. Zweifach) in 1936 — 1977, Renkin (E. M of Renkin) in 1952 — 1977, G.E. Palade in 1953 — 1977, Kasli-Smith (T. R. Casley-Smith) in 1961 — 1977, Viderkhilmom (Page A. Wiederhielm) in 1966 — 1977, etc.

Circulatory To. the essential role in the blood circulatory system belongs; they provide transcapillary exchange — penetration of the substances dissolved in blood from vessels in fabric and back. Continuous communication hemodynamic and exchange (metabolic) functions circulatory To. finds expression in their structure. According to microscopical anatomy, To. have an appearance of narrow tubes which walls are penetrated by submicroscopic «time». Capillary tubes happen rather direct, curved or twirled in a ball. Average length of a capillary tube from a precapillary arteriole to a post-capillary venule reaches 750 microns, and cross-sectional area — 30 microns 2 . Caliber To. on average there corresponds to diameter of an erythrocyte, however in different bodies internal diameter To. from 3 — 5 to 30 — 40 microns fluctuate.

Fig. 2. Diagrammatic representation of a structure of a wall of a circulatory capillary: 1 — an endothelial cover; 2 — the basal cover consisting of a basal membrane (3) and pericytes (4) in a gleam of a capillary erythrocytes are visible (5).
Fig. 3. The diffraction pattern of a fragment of a wall of a circulatory capillary from a parotid sialaden: I \a part of an erythrocyte in a gleam of a capillary; II \an endotheliocyte (1 — cytoplasm, 2 — mikropinotsitozny vesicles); III \basal membrane; IV \the pericyte located in the thickness of a basal membrane (3 — cytoplasm, 4 — a kernel, 5 — contact of a shoot of a pericyte with an endotheliocyte).
Fig. 4. Diffraction pattern of elements of a wall of circulatory capillaries: and — an intracerebral capillary (1 — a glikoproteidovy covering, 2 — an endotheliocyte); x 60 000; — intercellular contact in an endothelial cover of a glomerular capillary of a kidney (1 — cytoplasm of the next endotheliocytes, 2 — the contacting cytolemmas, 3 - an intermembrane interval); x 90 000; in and — glomerular capillaries of a kidney (1 - open fenestra; 2 — phrenic fenestra in cytoplasm of endotheliocytes); X 70 000; d — a wall of a sinusoidny capillary of a liver (1 — discontinuous contact between adjacent endotheliocytes 2); x 35 000.

As electronic and microscopic observations, a wall circulatory showed To., often called by the capillary membrane, consists of two covers: internal — endothelial and outside — basal. The diagrammatic representation of a structure of a wall circulatory To. more detailed is presented in the figure 2 — in figures 3 and 4.

The endothelial cover is formed by the flattened cells — endotheliocytes (see. Endothelium ). Number of the endotheliocytes limiting a gleam To., usually does not exceed 2 — 4. Width of an endotheliocyte fluctuates from 8 to 19 microns and length — from 10 to 22 microns. In each endotheliocyte allocate three zones: peripheral, zone of organellas, yadrosoderzhashchy zone. Thickness of these zones and their role in exchange processes are various. A half of volume of an endotheliocyte the kernel and organellas — a lamellar complex (Golgi's complex) occupy, mitochondrions, granular and not granular network, free ribosomes and polysom. Organellas are concentrated around a kernel, together with the Crimea make the trophic center of a cell. The peripheral zone of endotheliocytes performs generally exchange functions. In cytoplasm of this zone numerous mikropinotsitozny vesicles and fenestr (fig. 3 and 4) are located. The last represent submicroscopic (50 — 65 nanometers) openings which penetrate cytoplasm of endotheliocytes and are blocked by the thinned diaphragm (fig. 4, in, d) which is a derivative of a cellular membrane. The Mikropinotsitozny vesicles and fenestra participating in transendothelial transfer of macromolecules from blood in fabric and back in physiology are called large «holes». Each endotheliocyte is covered outside with the thinnest layer of the glycoproteins produced by it (fig. 4, a), the last play an important role in maintenance of constancy of the microenvironment surrounding cells of an endothelium and in adsorption of the substances transported through them. In an endothelial cover the next cells combine with the help of the intercellular contacts (fig. 4, b) consisting of cytolemmas of the adjacent endotheliocytes and intermembrane intervals filled with glycoproteins. These intervals in physiology most often are identified with small «time» through which they get water, ions and proteins with a low molecular weight. Capacity of interendothelial intervals is various that is explained by features of their structure. So, depending on thickness of an intertsellyulyarny crack distinguish interendothelial contacts of dense, slot-hole and discontinuous types. In dense contacts the intertsellyulyarny crack on a considerable extent is completely obliterated thanks to merge of cytolemmas of adjacent endotheliocytes. In slot-hole contacts the size of the smallest distance between membranes of the next cells fluctuates between 4 and 6 nanometers. In discontinuous contacts thickness of intermembrane intervals reaches 200 nanometers and more. Intercellular contacts of the last type in fiziol, literature are also identified with large «time».

A basal cover of a wall circulatory To. consists of cellular and noncellular elements. The noncellular element is presented basal membrane (see), surrounding an endothelial cover. Most of researchers considers a basal membrane as a peculiar filter 30 — 50 nanometers thick with the pore sizes equal — 5 nanometers, in Krom resistance to penetration of particles increases with increase in diameter of the last. In the thickness of a basal membrane cells — pericytes are located; they are called adventitious cells, Ruzhe's cells, or intramural pericytes. Pericytes have the extended form and are bent according to an external contour of an endothelial cover; they consist of a body and numerous shoots which braid an endothelial cover To. and, getting through a basal membrane, come into contacts with endotheliocytes. A role of these contacts as well as functions of pericytes, authentically it is not found out. It is suggested about participation of pericytes in regulation of growth of endothelial cells To.

Morphological and functional features of circulatory capillaries

Circulatory To. different bodies and fabrics have standard features of a structure that is connected with specifics of function of bodies and fabrics. It is accepted to distinguish three types K.: somatic, visceral and sinusoidny. The wall of circulatory capillaries of somatic type is characterized by a continuity endothelial and basal covers. As a rule, it is a malopronitsayema for large molecules of protein, but easily passes water with the crystalloids dissolved in it. To. such structure are found in skin, skeletal and smooth muscles, in heart and bark of hemicerebrums that corresponds to the nature of exchange processes in these bodies and fabrics. In a wall To. visceral type there are windows — fenestra. To. visceral type are characteristic of those bodies which cosecrete and soak up large amounts of water and the substances dissolved in it (digestive glands, intestines, kidneys) or participate in bystry transport of macromolecules (closed glands). To. sinusoidny type possess a big gleam (to 40 microns) that is combined with intermittence of their endothelial cover (fig. 4, e) and partial lack of a basal membrane. To. this type are found in marrow, a liver and a spleen. It is shown that through their walls not only macromolecules easily get (e.g., in a liver, edges produces the ground mass of proteins of a blood plasma), but also blood cells. The last is characteristic of the bodies participating in process of a hemopoiesis.

A wall To. has not only the general nature and close morfol, communication with surrounding connecting fabric, but is connected with it and is functional. Arriving from a circulatory bed through a wall To. liquid with the substances dissolved in it and oxygen are transferred by friable connecting fabric to all other fabric structures to surrounding fabric. Therefore, perikapillyarny connecting fabric as if supplements with itself a microcirculator bed. Structure and physical. - chemical properties of this fabric considerably define conditions of transport of liquid in fabrics.

Network K. is the considerable reflexogenic zone sending various impulses to nerve centers. On the course To. and the connecting fabric surrounding them there are sensitive nerve terminations. Apparently, among the last the important place is taken by the chemoceptors signaling about a condition of exchange processes. Effector nerve terminations at To. in most bodies are not found.

Network K., formed by tubes of small caliber where total indicators of cross-section and surface area considerably prevail over length and volume, creates optimum opportunities for an adequate combination of functions of a hemodynamics and transcapillary exchange. The nature of transcapillary exchange (see. Microcirculation ) depends not only on standard features of a structure of walls To.; not smaller value in this process belongs to bonds between separate To. Existence of bonds demonstrates integration To., and consequently, and about a possibility of their various combination funkts, activities. The philosophy of integration To. — their association in the certain sets making uniform functional network. In network situation separate To. unequally in relation to sources of delivery of blood and its outflow (i.e. to precapillary arterioles and post-capillary venules). This ambiguity is expressed that in one set To. are connected among themselves consistently thanks to what direct communications between the bringing and taking out micro vessels, and in other set are established To. are located in parallel in relation to To. the network stated above. Such topographical distinctions To. cause heterogeneity of distribution of flows of blood in network.

Fig. 5. The diagrammatic representation of a structure of a wall of a lymphatic capillary with elements of surrounding connecting fabric; 1 — an endotheliocyte; 2 — a gleam of a lymphatic capillary; 3 — collagenic protofibrils of connecting fabric; 4 — «anchor» filaments; 5 — connecting fabric.
Fig. 6. The diffraction pattern of elements of a wall of lymphatic capillaries and the connecting fabric surrounding them: and — an endotheliocyte (shooters specified mikropinotsitozny vesicles); x 20 000; — the «anchor» filaments (1) fixing an endotheliocyte (2) to the collagenic protofibrils surrounding it (3); x 50 000; in and — cytoplasm of endotheliocytes (1 — a lysosome, 2 — a residual little body); X 60 000.

Lymphatic capillaries

Lymphatic capillaries (fig. 5 and 6) represent system of the endothelial tubes closed since one end which perform drainage function — participate in absorption from fabrics of a filtrate of plasma and blood (liquid with the colloids and crystalloids dissolved in it), some uniform elements of blood (lymphocytes, erythrocytes), participate also in phagocytosis (capture of foreign debris, bacteria). Limf. To. take away a lymph through system intra-and ekstraorganny limf, vessels in the main limf, collectors — a chest channel and right limf. a channel (see. Lymphatic system ). Limf. To. penetrate fabrics of all bodies, except for a head and spinal cord, a spleen, cartilages, a placenta, and also a crystalline lens and a sclera of an eyeglobe. Diameter of their gleam reaches 20 — 26 microns, and a wall, unlike circulatory To., it is presented by only sharply flattened endotheliocytes (fig. 5). The last are about 4 times larger, than circulatory K. V endotheliocytes cells of an endothelium, except usual organellas and mikropinotsitozny vesicles, lysosomes and residual little bodies — the intracellular structures arising in the course of phagocytosis that is explained by participation limf meet. To. in phagocytosis. Other feature limf. To. consists available «anchor», or «harmonious», filaments (fig. 5 and 6) which are carrying out fixing of their endothelium to people around To. to collagenic protofibrils. Due to the participation in processes of absorption interendothelial contacts in their wall have various structure. In the period of an intensive resorption width of interendothelial cracks increases to 1 micron.

Methods of a research of capillaries

During the studying of a condition of walls To., forms of capillary tubes and space bonds between them widely use injection and bezynjektsionny techniques, various ways of reconstruction To., transmission and raster submicroscopy (see) in combination with methods of the morphometric analysis (see. Morphometry medical ) and mathematical modeling; for an intravital research K. the clinic applies microscopy (see. Kapillyaroskopiya ).

Pathology To. — see articles Inflammation ; Microcirculation ; Mikrotsirkulyation, pathology ; Swelled ; Permeability .


Bibliography: Alekseev P. P. Diseases of small arteries, capillaries and arteriovenous anastomosis, L., 1975, bibliogr.; Treasurers V. P. and Dzizinsky A. A. Clinical pathology of transcapillary exchange, M., 1975, bibliogr.; Kupriyanov V. V., Karaganov Ya. JI. and Kozlov V. I. Microcirculator bed, M., 1975, bibliogr.; Folkov B. and Neil E. Blood circulation, the lane with English, M., 1976; Chernukh A. M., Alexandrov P. N. ialekseev O. V. Mikrotsirkulyation, M., 1975, bibliogr.; Shakhlamov V. A. Capillaries, M., 1971, bibliogr.; Shushengko K. A. Circulatory capillaries, Novosibirsk, 1975, bibliogr.; Hammersen F. Anato-mie der terminalen Strombahn, Miinchen, 1971; By about g h A. Anatomie und Physio-logie der Capillaren, B. u. a., 1970, Bibliogr.; Microcirculation, ed. by G. Kaley a. B. M. Altura, Baltimore a. o., 1977; Simionescu N., SimionescuM. P an I a d e G. E. Permeability of muscle capillaries to small heme peptides, J. cell. Biol., v. 64, p. 586, 1975; Z w e i-fach B. W. Microcirculation, Ann. Rev. Physiol., v. 35, p. 117, 1973, bibliogr.

Ya. L. Karaganov.

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