What kind of blood goes to the liver? Portal circulation. Function of the portal and hepatic veins

The blood supply to the liver directly affects the quality of the functions performed by the organ. The process is carried out using a system of arteries and veins connecting the liver with other organs. Blood enters through two vessels and is distributed throughout the organ through branches of the left and right lobes.

Impaired tissue circulation deprives the liver of important nutrients and oxygen. The body's main filter does not perform the detoxification function well. As a result, the entire body suffers and overall health is impaired.

Venous blood, containing a mass of toxic substances, moves towards the liver from the intestines. It enters the liver directly through the portal vein. Next, there is a division into small interlobular veins.

Arterial blood enters the liver through the hepatic artery, which also branches into smaller interlobular arteries. Interlobular vessels of both types push blood into the sinusoids. There is mixed blood flow. It then drains into the central vein, and from there into the hepatic and inferior vena cava.

The liver, as a parenchymal organ, that is, an organ that does not have cavities, in its anatomy consists of structural units - lobules. Each lobule is formed by hepatocytes - specific cells. The prismatic lobules unite to form the right and left lobes of the liver. Blood supply is carried out directly by the system of arteries, veins, and connecting vessels.

The peculiarity of the blood supply to the liver is that the organ receives not only arterial blood, like all other internal organs, but mostly venous blood. The arteries supply nutrients and oxygen. And the veins carry blood for subsequent detoxification.

At an average blood flow rate of 100 ml per second, the blood supply is considered normal. As blood pressure changes, the speed changes. The smooth operation of arteries and veins helps regulate blood supply. In diseases of the biliary system, there is often a high blood flow rate in the portal vein and low blood flow in the arteries.

Portal circulation (synonymous with portal circulation) is a blood supply system to the abdominal organs that receive arterial blood from the celiac and mesenteric arteries.

From the celiac, mesenteric and splenic arteries, blood is under pressure of 110-120 mm Hg. Art. enters the so-called first network of capillaries of the portal bed, located in the intestines, stomach, pancreas and spleen. From there, under a pressure of 15-20 mm Hg. Art. it is directed to the venules, veins and then to the portal vein (see), where the pressure is 10-15 mm Hg. Art. From the portal vein, blood enters the so-called second network of capillaries of the portal bed, located in the liver, i.e., into the hepatic sinusoids, the pressure in which ranges from 6 to 12 mm Hg. Art. From there, the blood enters the inferior vena cava through the hepatic vein system, leaving the portal bed (color table).

Scheme of portal circulation: 1 - v. lienalis; 2 - v. mesenterica Inf.; 3 - v. mesenterica sup.; 4 - v. portae; 5 - branching of blood vessels in the liver; 6 - vv. hepaticae; 7 - v. cava inf.

One of the branches of the celiac artery - the hepatic artery - goes to the liver (see), where the arterial capillaries flow directly into the hepatic venules and sinusoids, i.e. into the second capillary network. The blood flowing through this artery is intended to supply the liver with oxygen and, accordingly, bypasses the first capillary network. The pressure difference in the initial and final parts of the portal bed is 100-110 mm Hg. Art., ensures forward blood flow. In humans, an average of 1.5 liters of blood flows through the portal bed per minute. The time of blood movement from the beginning of the mesenteric arteries through both capillary networks to the hepatic veins is 20 seconds; from the beginning of the hepatic artery through the liver vessels to the hepatic veins - 11 sec.

The portal bed is the main blood depot in the body. In the implementation of the deposition function, an important role is played by the diffuse vascular sphincter, located in the liver and regulating the outflow of blood from the portal bed, as well as the muscles of the mesenteric arteries, the tone of which regulates the amount of blood flow into the portal bed.

The ratio of the tone of the vessels through which the outflow and inflow of blood occurs determines its amount in the portal bed. Normally, this value is about 20% of the total amount of blood contained in the body, but in some pathological conditions it can increase to 60% or more.

An important part of the portal bed is the blood circulation in the liver, to which approximately 80% of the blood flows through the portal vein and 20% through the hepatic artery. The characteristics of blood circulation in the liver are closely related to the structure of the intrahepatic vessels. Thus, in the liver tissue there is a wide arteriovenous anastomosis between the branches of the portal vein and the hepatic artery. The normal significance of this anastomosis is that the liver cells receive not pure portal or arterial blood, but a mixture of portal and arterial blood, which is optimal for the liver cells to carry out their metabolic function. If the hepatic artery is ligated, the liver will be supplied with blood flowing only through the portal vein. If you create a porto-caval anastomosis of Eck (Eck fistula), thus directing the portal blood flow bypassing the liver, then the liver will be completely supplied with arterial blood. No pronounced disturbance of the metabolic and biliary functions of the liver is observed in either case. Consequently, in the liver there is interchangeability of portal and arterial blood flow. This is the basis for surgical operations used in the treatment of portal hypertension.

Small intrahepatic vessels - terminal venules of the portal system, sinusoids, central veins, branches of the hepatic artery - have great vasomotor activity. Adrenaline causes spasm of the sinusoids, opening of the exit sphincters and ejection of blood from the liver into the general circulation. The administration of a hypertonic NaCl solution or 40% glucose solution causes a spasm of the intrahepatic vessels, and after 20 minutes - their dilation. Cold irritation of skin receptors, injury to distant organs and tissues, blood loss lead to spasm of intrahepatic vessels; application of heat to the skin leads to their expansion. The third part of the inner surface of the liver sinusoids is covered with so-called Kupffer cells, which, being part of the reticuloendothelial system (see), phagocytose bacteria and fix foreign substances in their protoplasm.

Nervous regulation of portal circulation is carried out by autonomic centers under a certain degree of cortical control. In all parts of the portal bed there are numerous baroreceptors, irritation of which, when the portal vessels are stretched by increased pressure, leads to an increase in blood pressure in the systemic circulation. The sympathetic innervation of the portal bed originates from the neurons of the lateral columns of the III - XI thoracic segments of the spinal cord. When the sympathetic centers are excited, a sharp narrowing of the branches of the portal vein and liver sinusoids occurs; portal pressure increases accordingly. Excitation of the vagus nerve system leads to the opposite result.

The enrichment of liver tissue occurs through two vessels: the artery and portal vein, which are branched in the left and right lobes of the organ. Both vessels enter the gland through the “gate” located at the bottom of the right lobe. The blood supply to the liver is distributed in the following percentage: 75% of the blood passes through the portal vein, and 25% through the artery. involves the passage of 1.5 liters of valuable fluid every 60 seconds. when the pressure in the portal vessel is up to 10-12 mm Hg. Art., in the artery - up to 120 mm Hg. Art.

The liver suffers greatly from a lack of blood supply, and with this, the entire human body.

Features of the liver circulatory system

The liver plays a major role in metabolic processes occurring in the body. The quality of an organ’s functions depends on its blood supply. The liver tissues are enriched with blood from the artery, which is saturated with oxygen and nutrients. Valuable fluid enters the parenchyma from the celiac trunk. Venous blood, saturated with carbon dioxide and coming from the spleen and intestines, leaves the liver through the portal vessel.

The anatomy of the liver includes two structural units called lobules, which are similar to a faceted prism (the edges are created by rows of hepatocytes). Each lobule has a developed vascular network, consisting of an interlobular vein, artery, bile duct, and lymphatic vessels. The structure of each lobule suggests the presence of 3 blood streams:

• for the flow of blood serum to the lobules;
• for microcirculation inside the structural unit;
• to drain blood from the liver.

25-30% of the blood volume circulates through the arterial network under pressure up to 120 mmHg. Art., in the portal vessel - 70-75% (10-12 mm Hg. Art.). In sinusoids, the pressure does not exceed 3-5 mm Hg. Art., in the veins - 2-3 mm Hg. Art. If pressure increases, excess blood is released into the anastomoses between the vessels. After processing, arterial blood is directed into the capillary network, and then sequentially enters the hepatic vein system and accumulates in the lower hollow vessel.

The blood circulation rate in the liver is 100 ml/min, but with pathological dilatation of blood vessels due to their atony, this value can increase to 5000 ml/min. (about 3 times).

The interdependence of arteries and veins in the liver determines the stability of blood flow. When blood flow in the portal vein increases (for example, against the background of functional hyperemia of the gastrointestinal tract during digestion), the rate of movement of red liquid through the artery decreases. And, conversely, when the blood circulation rate in the vein decreases, perfusion in the artery increases.

The histology of the liver circulatory system suggests the presence of the following structural units:

• main vessels: hepatic artery (with oxygenated blood) and portal vein (with blood from unpaired peritoneal organs);
• an extensive network of vessels that flow into each other through lobar, segmental, interlobular, perilobular, capillary structures with a connection at the end into an intralobular sinusoidal capillary;
• efferent vessel - collecting vein, which contains mixed blood from the sinusoidal capillary and directs it to the sublobular vein;
• vena cava, designed to collect purified venous blood.

If for some reason blood cannot move at normal speed through the portal vein or artery, it is redirected to the anastomoses. A special feature of the structure of these structural elements is the ability to communicate with the blood supply system of the liver with other organs. True, in this case, the regulation of blood flow and redistribution of the red liquid is carried out without purifying it, so it, without lingering in the liver, immediately enters the heart.

The portal vein has anastomoses with the following organs:

• stomach;
• the anterior wall of the peritoneum through the periumbilical veins;
• esophagus;
• rectal section;
• the lower part of the liver itself through the vena cava.

Consequently, if a distinct venous pattern appears on the abdomen, resembling the head of a jellyfish, varicose veins of the esophagus and rectum are detected, it should be stated that the anastomoses are working in an enhanced mode, and in the portal vein there is a strong excess of pressure that prevents the passage of blood.

Regulation of blood supply to the liver

The normal amount of blood in the liver is considered to be 1.5 liters. Blood circulation is carried out due to the difference in pressure in the arterial and venous group of vessels. To ensure stable blood supply to the organ and its proper functioning, there is a special system for regulating blood flow. To do this, there are 3 types of regulation of blood supply, working through a special valve system of veins.

Myogenic

This regulatory system is responsible for muscular contraction of the vascular walls. Due to muscle tone, the lumen of blood vessels, when they contract, narrows, and when they relax, they expand. With the help of this process, the pressure and speed of blood flow increases or decreases, that is, the stability of the blood supply is regulated under the influence of:

• exogenous factors such as physical activity, rest;
• endogenous factors, for example, during pressure fluctuations, the development of various diseases.

Features of myogenic regulation:

• ensuring a high degree of autoregulation of hepatic blood flow;
• maintaining constant pressure in the sinusoids.

We suggest you read the article on the topic: “Blood supply to the liver” on our website dedicated to liver treatment.

The peculiarities of the blood supply to the liver reflect its important biological function of detoxification: blood from the intestines, containing toxic substances consumed from the outside, as well as waste products of microorganisms (skatole, indole, etc.) are delivered through the portal vein (v. portae) to the liver for detoxification. Further portal vein divides into smaller interlobular veins. Arterial blood enters the liver through its own hepatic artery (a. hepatica propria), branching to the interlobular arteries. Interlobular arteries and veins eject blood into the sinusoids, where mixed blood thus flows, draining into the central vein. The central veins collect into the hepatic veins and then into the inferior vena cava. In embryogenesis, the so-called liver approaches. Arantius duct, which carries blood to the liver for effective prenatal hematopoiesis.

Mechanism of detoxification

The neutralization of substances in the liver consists of their chemical modification, which usually includes two phases. In the first phase, the substance undergoes oxidation (removal of electrons), reduction (gain of electrons) or hydrolysis. In the second phase, a substance is added to the newly formed active chemical groups. Such reactions are called conjugation reactions, and the process of addition is called conjugation.

Liver diseases

Cirrhosis of the liver- chronic progressive liver disease, characterized by a violation of its lobular structure due to the proliferation of connective tissue and pathological regeneration of the parenchyma; manifested by functional liver failure and portal hypertension.

The most common causes of the disease are chronic alcoholism (the proportion of alcoholic cirrhosis of the liver in different countries ranges from 20 to 95%), viral hepatitis (accounts for 10-40% of all liver cirrhosis), the presence of helminths in the liver (most often opisthorchis, fasciola, clonorchis , Toxocara, Notocotilus), as well as protozoa, including Trichomonas.

The occurrence of benign adenomas, angiosarcomas of the liver, and hepatocellular carcinoma is associated with human exposure to androgenic steroid contraceptives and anabolic drugs.

Main symptoms of liver cancer:

weakness and decreased performance;

weight loss, loss of body weight, and then severe cachexia, anorexia.

nausea, vomiting, sallow skin color and spider veins;

complaints of a feeling of heaviness and pressure, dull pain;

elevated temperature and tachycardia;

jaundice, ascites and dilatation of the superficial veins of the abdomen;

gastroesophageal bleeding from varicose veins;

skin itching;

gynecomastia;

flatulence, intestinal dysfunction.

Liver hemangiomas- abnormalities in the development of liver vessels. Main symptoms of hemangioma:

heaviness and feeling of fullness in the right hypochondrium;

dysfunction of the gastrointestinal tract (loss of appetite, nausea, heartburn, belching, flatulence).

constant pain in the right hypochondrium;

a quickly onset feeling of satiety and abdominal discomfort after eating;

weakness;

increased sweating;

loss of appetite, sometimes nausea;

shortness of breath, dyspeptic symptoms;

soreness;

a feeling of heaviness, pressure in the right hypochondrium, sometimes in the chest;

weakness, malaise, shortness of breath;

recurring urticaria, diarrhea, nausea, vomiting.

Other liver infections: clonorchiasis, opisthorchiasis, fascioliasis.

The blood supply to the liver directly affects the quality of the functions performed by the organ. The process is carried out using a system of arteries and veins connecting the liver with other organs. Blood enters through two vessels and is distributed throughout the organ through branches of the left and right lobes.

Impaired tissue circulation deprives the liver of important nutrients and oxygen. The body's main filter does not perform the detoxification function well. As a result, the entire body suffers and overall health is impaired.

Arterial blood enters the liver through the hepatic artery, which also branches into smaller interlobular arteries. Interlobular vessels of both types push blood into the sinusoids. There is mixed blood flow. It then drains into the central vein, and from there into the hepatic and inferior vena cava.

Liver circulation diagram The liver, as a parenchymal organ, that is, an organ that does not have cavities, in its anatomy consists of structural units - lobules. Each lobule is formed by hepatocytes - specific cells. The prismatic lobules unite to form the right and left lobes of the liver. Blood supply is carried out directly by the system of arteries, veins, and connecting vessels.

The peculiarity of the blood supply to the liver is that the organ receives not only arterial blood, like all other internal organs, but mostly venous blood. The arteries supply nutrients and oxygen. And the veins carry blood for subsequent detoxification.

At an average blood flow rate of 100 ml per second, the blood supply is considered normal. As blood pressure changes, the speed changes. The smooth operation of arteries and veins helps regulate blood supply. In diseases of the biliary system, there is often a high blood flow rate in the portal vein and low blood flow in the arteries.

Function of the portal and hepatic veins

The portal vein is one of the largest vessels of the portal circulatory system. The venous trunk collects blood from the digestive organs and carries it to the liver. An additional circle of blood circulation is created, ensuring the purification of the blood plasma from toxins and harmful metabolic products.

Liver pathologies lead to dysfunction of its blood vessels. This means metabolic disorders and, as a consequence, constant intoxication of the body with metabolites. The portal vein serves as the main blood depot, which is why its proper functioning is so important.

If blood cannot enter the liver due to inflammatory diseases or thrombosis, it does not accumulate in the afferent vessel, but moves along bypass paths. Venous tracts connect the portal vein with the vessels of the stomach, esophagus, intestines and other organs. But such a scheme is unsafe for health, since the blood enters the heart in a form that is not purified from toxins and poisons.

Bypass paths, called anastomoses, function fully only in pathologies. Thus, cirrhosis of the liver can be suspected when the vessels of the anterior abdominal wall are filled with blood.

The portal vein refers to the afferent vessels that carry blood to the organ. And the venous outflow is formed from the hepatic veins. Along these paths it leaves the organ and enters the systemic circulation.

Work of arteries

The hepatic arteries work according to the following scheme:

1. The hepatic artery, connected to the abdominal aorta, carries arterial blood to the liver.
2. Along the way, the hepatic artery supplies blood to the gallbladder and stomach.
3. Before entering the liver, the artery divides into left and right branches.
4. There is a blood supply to all lobes of the liver, as well as the gallbladder.

The connecting function between the arteries and veins in the liver is played by sinusoidal capillaries. They ensure metabolic processes between blood and tissues. This is an important vascular link that distributes mixed blood enriched with oxygen throughout the parenchyma.

Blood circulation in lobules

The liver consists of small lobules surrounded by a network of vessels. These vessels have a special structure, due to which the blood is cleansed of toxins.

The main vessels carrying blood to the liver are divided into:

• equity;
• interlobular;
• intralobular;
• segmental branches.

Vessels with a thin muscle layer provide filtration. The central vein, into which the capillaries merge, is devoid of muscle tissue. When leaving the organ, the blood is dissolved through the hepatic veins with a full muscle layer. Next it enters the inferior vena cava, and from there into the right atrium.

Regulation of blood circulation

With normal blood circulation, the blood volume in the liver is about 1.5 liters. Blood circulation itself becomes possible thanks to vascular resistance in groups of arteries and veins.

For a stable blood circulation process in the liver, the body provides a blood flow system with three types of regulation. The essence is to maintain a constant volume of blood in the liver and ensure its movement through the vessels at a stable speed.

Myogenic regulation

Myogenic, or muscular, regulation means the implementation of hepatic blood flow by contracting the muscular layer of the vascular walls. When the muscles contract, the lumen narrows. When relaxing, the lumen expands. This process controls the pressure and speed of blood flow.

The following factors are responsible for the stability of the process:

• external, which include successive periods of physical activity and rest;
• internal, which depend on the presence or absence of chronic diseases and inflammation, and on changes in blood pressure.

Thanks to myogenic regulation, a constant level of compression is maintained in the sinusoids - pressure on the walls of blood vessels.

Humoral regulation

Occurs due to hormonal effects on blood vessels. Regulators are biological substances:

• adrenaline reduces pressure on the walls of blood vessels, acting on muscle tissue receptors and relaxing it;
• angiotensin and norepinephrine narrow the lumen of arteries and veins, thereby reducing blood flow pressure;
• acetylcholine expands the lumen of blood vessels, improves blood circulation in tissues;
• Insulin and thyroxine slow down arterial blood flow, but speed up metabolic processes.

The speed of blood flow and the tone of blood vessels are also affected by hormones that enter the body with foods and medications.

Humoral regulation is the basis of the body's reactions to most external factors. The production of hormones depends on the normal functioning of the endocrine system.

Nervous regulation

The basis of nervous regulation is the connection of organs and tissues with the central nervous system. In the case of the liver, there are sympathetic and parasympathetic connections. In the first case, process control leads to a narrowing of the vascular lumen and a decrease in the volume of incoming blood.

In the second, nerve impulses are supplied from the vagus nerve, but they do not affect the blood supply process.

The blood supply to the liver differs from the standard pattern for other internal organs. Blood inflow occurs through veins and arteries, outflow occurs only through veins. Due to the functional characteristics of the organ, the blood is filtered from toxins and metabolic products, and is distributed in a purified form through the circulatory system throughout the body.

Blood supply to the liver is carried out in two ways - with blood flowing through a large artery and through the portal vein. These two links branch in the left and right lobes of the body's natural filter. Both the artery and the portal vein provide arterial blood flow to the veins, arteries, and capillaries. In the absence of full microcirculation, the liver suffers from a lack of nutrients and oxygen. Due to this, not only she suffers, but the entire body as a whole.

Blood supply to the liver is carried out in two ways - with blood flow through a large artery and through the portal vein

Features of blood supply

It is important to know the peculiarities of the blood supply to the liver, what happens if blood does not enter the liver through the vessels. The body's natural filter is a key link in all metabolic processes. How well the regulation of blood supply is established and the volume of fluid in the cavity of the left and right lobes of the liver directly determines how well all the functions of the organ are performed.

The enrichment of the liver tissues with blood fluid comes from a large artery, which also provides oxygen and nutrients. Human physiology is designed in such a way that blood enters the parenchyma from the trunk of the womb. And the discharge of venous fluid and carbon dioxide occurs through the portal canal, which comes from the spleen and intestinal tract.

The structure of the liver is created in such a way that there are two lobules, the edges of which are created from rows of hepatocytes. Both the right and left hepatic lobes consist of a branched vascular network and lymphatic passages. And each of them has three main bloodstreams, the task of which is:

1. The flow of blood serum to the lobules themselves.
2. Microcirculation in the cell cavity.
3. Removal from the organ.

The blood flow rate is 100 ml per 1 minute; with an increase in blood pressure and with strong vasodilation, it can increase, accumulating in the hollow vessel of the gland. Regulation of blood supply occurs through the coordinated work of arterial and venous ducts. If the speed of blood flow in the portal vein increases, it decreases in the arteries. This happens with diseases of the digestive system.

Portal vein in the process of blood circulation

The portal vein is one of the main components of the circulatory system in the liver. The dimensions of this artery allow the normal functioning of the digestive system, and the normal function of detoxifying blood fluid is also performed. In the presence of any pathological processes in this vessel, serious disruptions occur in the functioning of all systems.

The portal vein is one of the main components of the circulatory system in the liver

It accumulates fluid that comes from the abdominal organs. This vessel creates an additional circle of blood circulation, which ensures the purification of the plasma from toxic substances and unnecessary metabolic processes. Without this vein, these substances will immediately enter the heart and lungs. This is how the anatomy of internal organs was created.

With any pathologies of the liver, its vessels also suffer, due to which deterioration occurs in the functioning of the digestive system. The result is severe intoxication with metabolites. Therefore, in the treatment of diseases, it is important to control the full microcirculation of the portal vein systems, which function as a blood depot.

Types of regulations

Regulation of blood supply occurs in several ways. Normally, the volume of blood fluid in the body’s natural filter is one and a half liters. Blood circulation is carried out with the help of vascular resistance in the arterial and venous groups. In order for blood to flow in and out of the body’s natural filter normally and all processes to be stable, it has a certain blood flow system, which is represented by three types of regulation of blood supply.

Myogenic

Hepatic blood flow is carried out by muscular contraction of the walls of blood vessels. The muscles are in good shape, the lumen narrows during muscle contraction, and when it relaxes, the lumen expands. This process provides an increase or decrease in compression and blood flow speed. The stability of the blood supply is regulated by the following factors:

Hepatic blood flow is carried out by muscle contraction of the walls of blood vessels

• external – physical activity and rest, which is why it is very important to include in the daily diet not only a period of relaxation, but also periods of stress;
• internal – changes in blood pressure, exacerbation of chronic diseases (regardless of the organ or system in which they develop).

Myogenic regulation ensures regulation of blood flow and maintains constant compression in the sinusoids.

Humoral

Humoral regulation is carried out with the help of hormonal substances in the body:

1. Adrenalin. Its production occurs during intense emotional stress. It affects the receptors of the portal vein, due to which the smooth muscles inside the walls of the veins, arteries and capillaries relax, and the pressure in them decreases.
2. Norepinephrine, angiotensin. They affect the system of veins and arteries, against which the lumen narrows, resulting in a decrease in fluid volume.
3. Acetylcholine. Thanks to this hormonal substance, the lumen in the arteries expands, and the organ’s nutrition with blood fluid improves.
4. Metabolites and hormones found in tissues. Promote the expansion of arterioles and narrowing of portal venules. The speed of blood flow in the veins decreases, and the speed in the arteries increases, the amount of fluid in them increases.
5. Thyroxine, insulin and others. With their help, metabolic processes are accelerated and blood flow is increased.

Nervous

This type of regulation plays a secondary role. There are sympathetic and parasympathetic innervation. The first is responsible for narrowing the lumen of blood vessels, reducing volume, and the second ensures the flow of nerve impulses from the vagus nerve.

These impulses do not have a direct effect on the flow of blood and oxygen into the body’s natural filter. The humoral and myogenic systems are important links, since with their help the organ is fully saturated with all the necessary substances for normal functioning.

Video

Liver: topography, structure, functions, blood supply, innervation, regional lymph nodes.

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The blood supply to the liver is carried out by a system of arteries and veins, which are connected to each other and to the vessels of other organs. This organ performs a huge number of functions, including the detoxification of toxins, the synthesis of proteins and bile, and the storage of many compounds. Under conditions of normal blood circulation, it does its job, which has a positive effect on the condition of the whole organism.

How do blood circulation processes occur in the liver?

The liver is a parenchymal organ, that is, it does not have a cavity. Its structural unit is a lobule, which is formed by specific cells, or hepatocytes. The lobule has the shape of a prism, and neighboring lobules are combined into lobes of the liver. The blood supply to each structural unit is carried out using the hepatic triad, which consists of three structures:

• interlobular vein;
• arteries;
• bile duct.

The peculiarities of the blood supply to the liver are that it receives blood not only from arteries, like other organs, but also from veins. Although the veins carry more blood (about 80%), the arterial blood supply is no less important. The arteries carry blood saturated with oxygen and nutrients.

Main arteries of the liver

Arterial blood enters the liver from vessels that originate from the abdominal aorta. The main artery of the organ is the hepatic one. Along its length, it gives blood to the stomach and gall bladder, and before entering the gate of the liver or directly in this area, it is divided into 2 branches:

• the left hepatic artery, which carries blood to the left, quadrate and caudal lobes of the organ;
• the right hepatic artery, which supplies blood to the right lobe of the organ and also gives off a branch to the gallbladder.

The arterial system of the liver has collaterals, that is, areas where neighboring vessels are united through collaterals. These may be extrahepatic or intraorgan associations.

Large and small veins and arteries take part in the blood circulation of the liver

Veins of the liver

The veins of the liver are usually divided into afferent and efferent. Along the afferent tract, blood moves to the organ, and along the efferent tract, it moves away from it and carries away the final products of metabolism. Several main vessels are associated with this organ:

• portal vein - an afferent vessel that is formed from the splenic and superior mesenteric veins;
• hepatic veins are a system of drainage tracts.

The portal vein carries blood from the organs of the digestive tract (stomach, intestines, spleen and pancreas). It is saturated with toxic metabolic products, and their neutralization occurs in the liver cells. After these processes, the blood leaves the organ through the hepatic veins, and then participates in the systemic circulation.

Diagram of blood circulation in the liver lobules

The topography of the liver is represented by small lobules, which are surrounded by a network of small vessels. They have structural features that help cleanse the blood of toxic substances. When entering the portal of the liver, the main afferent vessels are divided into small branches:

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• equity,
• segmental,
• interlobular,
• intralobular capillaries.

These vessels have a very thin muscle layer to facilitate blood filtration. At the very center of each lobule, the capillaries merge into a central vein, which is devoid of muscle tissue. It flows into the interlobular vessels, and they, accordingly, into the segmental and lobar collecting vessels. Leaving the organ, the blood is distributed through 3 or 4 hepatic veins. These structures already have a full muscle layer and carry blood into the inferior vena cava, from where it enters the right atrium.

Portal vein anastomoses

The blood supply to the liver is adapted to ensure that the blood from the digestive tract is cleared of metabolic products, poisons and toxins. For this reason, stagnation of venous blood is dangerous for the body - if it collects in the lumen of blood vessels, toxic substances will poison the person.

Anastomoses are bypass routes for venous blood. The portal vein is connected to the vessels of some organs:

• stomach;
• anterior abdominal wall;
• esophagus;
• intestines;
• inferior vena cava.

If for some reason the fluid cannot enter the liver (due to thrombosis or inflammatory diseases of the hepatobiliary tract), it does not accumulate in the vessels, but continues to move along bypass paths. However, this condition is also dangerous because the blood does not have the opportunity to get rid of toxins and flows into the heart in an unclean form. Portal vein anastomoses begin to function fully only in pathological conditions. For example, with cirrhosis of the liver, one of the symptoms is the filling of the veins of the anterior abdominal wall near the navel.

The most important processes occur at the level of liver lobules and hepatocytes

Regulation of blood circulation processes in the liver

The movement of fluid through the vessels occurs due to the pressure difference. The liver constantly contains at least 1.5 liters of blood, which moves through large and small arteries and veins. The essence of blood circulation regulation is to maintain a constant amount of fluid and ensure its flow through the vessels.

Mechanisms of myogenic regulation

Myogenic (muscular) regulation is possible due to the presence of valves in the muscular wall of blood vessels. When muscles contract, the lumen of the blood vessels narrows and fluid pressure increases. When they relax, the opposite effect occurs. This mechanism plays a major role in the regulation of blood circulation and is used to maintain constant pressure in different conditions: during rest and physical activity, in heat and cold, with increases and decreases in atmospheric pressure and in other situations.

Humoral regulation

Humoral regulation is the effect of hormones on the condition of the walls of blood vessels. Some of the biological fluids can affect veins and arteries, expanding or narrowing their lumen:

• adrenaline - binds to adrenergic receptors in the muscular wall of intrahepatic vessels, relaxes them and provokes a decrease in blood pressure;
• norepinephrine, angiotensin - act on veins and arteries, increasing fluid pressure in their lumen;
• acetylcholine, products of metabolic processes and tissue hormones - simultaneously dilates arteries and constricts veins;
• some other hormones (thyroxine, insulin, steroids) - provoke an acceleration of blood circulation and at the same time a slowdown in blood flow through the arteries.

Hormonal regulation underlies the response to many environmental factors. The secretion of these substances is carried out by endocrine organs.

Nervous regulation

Mechanisms of nervous regulation are possible due to the peculiarities of the innervation of the liver, but they play a secondary role. The only way to influence the condition of the hepatic vessels through the nerves is to irritate the branches of the celiac nerve plexus. As a result, the lumen of the vessels narrows, the amount of blood flow decreases.

Blood circulation in the liver differs from the usual pattern that is typical for other organs. The inflow of fluid is carried out by veins and arteries, and the outflow is carried out by the hepatic veins. During circulation in the liver, the fluid is cleared of toxins and harmful metabolites, after which it enters the heart and further participates in blood circulation.