PORTAL BLOOD CIRCULATION

From Big Medical Encyclopedia

PORTAL BLOOD CIRCULATION [late lat. (vena) of portae a portal vein] — the conditional zone of the blood circulatory system limited to the level of an otkhozhdeniye from an aorta of a celiac trunk and an upper mesenteric artery and the place of falling of hepatic veins into the lower vena cava. The item to. represents area of blood circulation of a liver, stomach, intestines, pancreas and spleen (fig. 1).

Fig. 1. The diagrammatic representation of the arteries and veins which are logging in portal blood circulation: 1 — a ventral aorta; 2 — a celiac trunk; 3 — an upper mesenteric artery; 4 — the lower mesenteric artery and a vein; 5 — an upper mesenteric vein; 6 — a splenic vein; 7 — a portal vein; 8 — a hepatic vein; 9 — branching of a portal vein in a liver; 10 — hepatic veins; 11 — the lower vena cava.

In a wedge, practice the term «portal blood circulation» is widely used in narrower sense — for designation of blood circulation in system of a portal vein.

The significant contribution to P.'s studying to. N. V. Ekk, I. P. Pavlov, H brought. N. Burdenko, B. A. Long Saburov, H. Elias, etc. In V. V. Larin's works, T. 3. Meersona (1965), A. A. Krivchik (1979), Fischer (A. Fischer, 1961), etc. described P.'s features to. normal and at various patol, states.

Blood in system P. to. passes through two networks of capillaries. The first network located in walls of digestive organs provides their absorbing, secretory and motor functions. Capillaries of a spleen also belong to this network. The second network of capillaries is located directly in a parenchyma of a liver and provides exchange and excretory its functions. From portal vein (see) blood gets to the lower vena cava (see. Venas cava ) also is returned to heart only having passed through a liver that prevents intoxication of an organism the toxic products which are formed in went. - kish. path. The main body of P. to. — liver (see), in to-ruyu blood from two systems of vessels (arterial — from own hepatic artery, venous — from a portal vein) with uniform system of drainage through hepatic veins arrives. Through a portal vein there pass 70 — 80% of all blood coming to a liver, through own hepatic artery — 20 — 30%.

Essential feature of blood circulation in a liver is broad communication between branchings of a portal vein and own hepatic artery with education in segments of a liver of sinusoidny capillaries, to membranes to-rykh directly prilezhat hepatic cells (hepatocytes). Thus, to hepatocytes the mixed blood arrives. A big surface (the total area of a surface of sinusoidny capillaries of a liver makes apprx. 200 m 2 ) contacts of blood with hepatocytes and the slowed-down blood stream in sinusoidny capillaries provide optimal conditions for exchange and synthetic processes. From sinusoidny capillaries blood flows in the central veins, then in hepatic veins and the lower vena cava.

Fig. 2. The diagrammatic representation of system of sphincters at the level of intra hepatic circulation: 1 — an interlobular vein, 2 — the central vein, 3 — a sinusoidny capillary, 4 — a portal vein, 5 — a hepatic artery, 6 — an entrance venous sphincter, 7 — entrance arterial sphincters, 8 — an output sphincter in the place of falling of a sinusoidny capillary into the central vein, 9 — an output sphincter in the field of connection of the central and interlobular veins.

Neyrogumoralnaya and hemodynamic regulation of P. to. it is carried out through system of the sphincters located on the course of a portal bed (fig. 2) and regulating inflow and outflow of blood. This system normal provides adaptation of a blood-groove to activity of abdominal organs, and also performs function of deposition of blood in a portal bed and a liver. Distinguish entrance and output sphincters. Entrance sphincters are located in places of transition of small branchings of a portal vein and arterioles in sinusoidny capillaries, and output sphincters — in the field of falling of sinusoidny capillaries into the central vein and the central vein in interlobular. Reduction of sphincters happens periodically. At reduction of output sphincters sinusoidny capillaries are filled with blood, at increase in a tone of entrance sphincters blood from sinusoidny capillaries flows. A role of an additional sphincter of a portal bed is played by a muscular layer of an average cover of a wall of the arteries and arterioles which are a part of the system P. to. The tone of this layer also determines the size of inflow of blood to a portal bed.

One of the most important conditions of normal blood circulations (see) in any vascular system existence of a difference of pressure between various points of this system is. In system P. to. an arterial blood under pressure of 110 — 120 mm of mercury. comes to the first network of capillaries where it goes down to 10 — 15 mm of mercury. In a portal vein pressure makes 5 — 10 mm of mercury., and in hepatic veins of 0 — 5 mm of mercury. Thus, the difference of pressure in initial and final departments of a portal bed providing progress of blood makes St. 100 mm of mercury. Extra organ vessels of a liver also have a muscular layer that promotes the propulsive movement of blood. It is possible that current of portal blood is promoted by rhythmical reductions of a spleen.

Average peripheral speed in system of a portal vein makes 15 cm/sec. Speed of the movement of blood in sinusoidny capillaries of a liver is slowed down thanks to what time of contact of blood with hepatocytes increases. In total through a portal bed 1500 ml of blood in 1 min. proceed on average that makes U4 — bonds of minute volume of heart.

An innervation and nervous control of P. to. carries out the celiac texture incorporating both sympathetic, and parasympathetic fibers. The irritation of sympathetic fibers and a vokrugarte-rialny texture leads to sharp narrowing of sinusoidny capillaries, small branchings of a portal vein and entrance sphincters and, respectively, to increase in pressure in system of a portal vein. The irritation of a vagus nerve causes opposite effect. An important role in P.'s regulation to. the endocrine system plays. Administration of adrenaline or noradrenaline in the general blood stream causes narrowing of afferent vessels of a liver and sinusoidny capillaries, a spasm of entrance sphincters and relaxation of output sphincters. At the same time pressure in a portal vein increases. Serotonin considerably narrows vessels of system of a portal vein, AKTG considerably increases a hepatic blood stream. Acidosis, hypoxia, hypothermia and other factors worsen microcirculation in a liver.

With age, according to Dermot (M. of Dermott, 1974) and Altmanna (H. W. Altmann, 1975), observes a nek-swarm P.'s decrease to. In 1974 Yu. A. Yershov by means of a method of correlation analysis established that P.'s volume to. significantly depends on the size of cordial emission. At advanced age the size of cordial emission decreases that leads to decrease in portal blood circulation.

Disturbance of a blood-groove in system P. to. it is caused by changes of amount of the inflowing blood, resistance to its outflow of side pressure upon walls of vessels and rheological properties of blood.

Intake of blood in a portal vein can increase in the course of digestion, however in this case it exceeds a blood stream at rest no more than for 50%. Significantly the krovenapolneniye of venous vessels of abdominal organs at inflammatory processes increases, napr, peritonitis. Reduction of intake of blood in a portal vein is possible at jumps of position of a body (an orthostatic collapse), at ischemia of intestines as a result of blood loss, a severe mechanical injury, etc.

The disturbances of outflow of blood from system of vessels of a portal vein leading usually to build-up of pressure in it (see. Portal hypertensia ), can be caused by heart failure, narrowing or thrombosis of hepatic veins, and also increase of resistance to a blood-groove in vessels of a liver as a result of changes of their tone under the influence of nervous and especially humoral factors or narrowing of their gleam, napr, at development of cirrhosis (see. Cirrhoses of a liver ).

A big role in disturbance of a blood-groove in system P. to. plays change of intra belly pressure. During a breath inflow of blood to a portal vein increases and outflow in system of a hepatic vein decreases; at an exhalation inverse relation takes place. Increase in frequency and depth of breath can influence a portal blood stream considerably. Increase in intra belly pressure at ascites (see), a meteorism, an atony of intestines, etc. is also followed by disturbances of a portal blood-groove.

Changes of rheological properties of blood, napr, increase in its dynamic viscosity, promote delay of a blood-groove in a portal vein.

Liver (see) it is supplied with oxygen through system of a portal vein and hepatic artery. Regulation of the oxygen mode of a liver is carried out due to change of inflow of blood through system of a hepatic artery. Restriction of a portal blood-groove and a hypoxia of a liver, napr, at extreme states, lead to increase in a share of arterial blood supply up to 80% and more. Activation of an arterial blood-groove is promoted also by action on vessels of metabolites and physiologically active agents, in particular ferritin. On the other hand, activation of an arterial blood-groove and increase in pressure in sinusoidny capillaries of a liver lead to restriction of intake of blood in them from a portal vein and to build-up of pressure in it.

At difficulty of outflow of blood through hepatic veins or increase of its inflow in a liver about 20% of total amount of blood can be deposited (see. Blood depot ). Vessels of a liver, performing function of locks, play a large role in regulation system hemodynamics (see). The delay of blood in sinusoidny capillaries of a liver increases an ekstravazation of liquid in perisinusoidalny spaces that matters in regulation water salt metabolism (see). The spleen and vessels of intestines takes part in deposition of blood in a portal bed.

Frustration of a portal blood-groove are followed by disturbances of exchange processes in a liver, essential disturbances of its functions. So, during the imposing of an ekkovsky anastomosis a blood stream through a liver and oxygen consumption decrease by 50%; it does not lead to the menacing disturbances of carbohydrate and lipidic metabolism, but considerably influences protein metabolism and, first of all, synthesis of urea.

At the expressed disorders of blood supply of a liver, first of all arterial, and development of a deep hypoxia energy balance and processes of interamination and protein synthesis interfaced to it, especially a blood plasma considerably suffers.

To the most informative and widespread methods of a research P. to. belong splenoportografiya (see), intraoperative portografiya (see) and a splenoporto-manometriya (see. Portal hypertensia ), allowing to judge a hemodynamics of a portal bed and localization patol, the process blocking a portal blood stream. Features of arterial circulation reflect tseliakografiya (see) and reogepatografiya (see). Sounding of hepatic veins (tonometry, contrasting) gives information on a condition of the removing system of a portal bed. Tests with bromsulfaleiny and to radioactive Bengalese pink allow to judge a volume blood-groove in a liver.



Bibliography: Long Saburov B. A. An anastomosis and ways of roundabout blood circulation at the person, page 97, D., 1956; A. S's Logins. and Fomichev V. I. Hemodynamic and functional changes at chronic hepatitis and cirrhosis, in book: Diseases of the digestive system, under the editorship of A.S. Loginov, page 28, M., 1977; P and r and N V. V. and Meerson F. 3. Sketches of clinical physiology of blood circulation, page 191, M., 1965; Seleznyov S.A. A liver in dynamics of traumatic shock, L., 1971, bibliogr.; Fischer A. Physiology and experimental pathology of a liver, the lane with it., Budapest, 1961; Folkov B. and Neil E. Blood circulation, the lane with English, M., 1976; E to N. K to a question of bandaging of a portal vein, Voyen. - medical zhurn., p. 130, book 11, otd. 2, page 1, 1877; Elias H. a. Selkurt E. E. Microscopic and. submicroscopic anatomy, in book: Blood vessels and lymphatics, ed. by D. I. Abramson, p. 360, N. Y. — L., 1962; Handbook of physiology, Sect. 2 — Circulation, ed. by W. F. Hamilton, v. 2, p. 1387, Washington, 1963; Me Dermott W. Surgery of the liver and portal circulation, Philadelphia,

1974.


M. D. Patsiora; S. A. Seleznyov (stalemate. physical.).

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