Structure of the liver, size of the liver, segments of the liver. Vascular system of the liver. Arterial blood supply. Portal vein. Biliary system. Ultrastructure of the liver.

Anatomy of the liver

Liver- one of the largest organs of the human body, playing an important role in digestion and metabolism. It is difficult to name another organ with as wide a variety of functions as the liver.

The relative size and weight of the liver are subject to significant fluctuations depending on age. The weight of the liver of an adult is 1300 - 1800. The liver of newborns and children in the first month of life occupies 1/2 or 1/3 of the abdominal cavity, averaging 1/18 of the body weight, and in adults it is only 1/36 of the body weight. However, already in three-year-old children, the liver has the same relationship with the abdominal organs as in adults, although its edge protrudes more from under the costal arch due to the child’s short chest.

The liver is covered by peritoneum on all sides, with the exception of the gate and part of the posterior surface. The parenchyma of the organ is covered with a thin, durable fibrous membrane (Glisson's capsule), which enters the parenchyma of the organ and branches in it.

Skeletotopy of the liver

The liver is located directly below the diaphragm in the upper right abdominal cavity, a small part of the organ in an adult extends to the left of the midline. The organ has stable landmarks in relation to the skeleton, which are used to determine its boundaries (Fig. 1). The upper border of the liver on the right with maximum exhalation is located at the level of the 4th intercostal space along the right nipple line, the upper point of the left lobe reaches the 5th intercostal space along the left parasternal line. The upper edge of the liver has a slightly oblique direction, running along a line from the fourth right rib to the cartilage of the fifth left rib. The anterior inferior edge of the liver on the right along the axillary line is at the level of the 10th intercostal space, its projection coincides with the edge of the costal arch along the right nipple line. Here the anterior edge departs from the costal arch and stretches obliquely to the left and upward; along the midline it is projected in the middle of the distance between the navel and the base of the xiphoid process. Next, the anterior edge of the liver crosses the left costal arch and at the level of the VI costal cartilage along the left parasternal line passes into the upper edge.

Determination of the projection of the anterior edge of the liver very important when performing percutaneous needle biopsy of the liver. The anterior projection of the liver has the appearance of an almost right-angled triangle, mostly covered by the chest wall, only in the epigastric region the lower edge of the liver extends beyond the costal arches and is covered by the anterior abdominal wall. The posterior projection of the liver occupies a relatively narrow strip. The upper edge of the liver is projected at the level of the lower edge of the IX thoracic vertebra, and the lower border runs along the middle of the XI thoracic vertebra.

The location of the liver changes depending on the position of the body. In a vertical position, the liver lowers slightly, and in a horizontal position it rises. The displacement of the liver during breathing is used during its palpation: in most cases, it is possible to determine its lower edge during the deep inspiration phase.

Rice. 1

It is important to remember the variations in the position of the liver in relation to the sagittal plane of the body; distinguish between the right-sided and left-sided position of the liver. In the right-sided position, the liver lies almost vertically and has a highly developed right lobe and a reduced left one. In some cases, the entire organ does not cross the midline, being located in the right half of the abdominal cavity. In a left-sided position, the organ lies in a horizontal plane and has a well-developed left lobe, sometimes even extending beyond the spleen. These variations in the position of the liver must be taken into account when assessing the results of scanning and echolocation of the organ.

Segmental division of the liver

According to external signs, the liver is divided into right and left lobes of unequal size. On the upper convex surface, the border between the lobes is the place of attachment of the falciform ligament; on the lower surface, the border is the left and right longitudinal grooves. In addition, the quadrate and caudal lobes are distinguished, which were previously classified as the right lobe. The quadrate lobe is located between the anterior sections of two longitudinal grooves. The caudal lobe of the liver is located between the posterior sections of the longitudinal grooves. The gallbladder is located in the anterior part of the recess on the lower surface of the right lobe of the liver. In the deep transverse groove on the lower surface of the right lobe there is the gate of the liver. Through the gate, the hepatic artery and portal vein with their accompanying nerves enter the liver, and the common hepatic bile duct and lymphatic vessels exit.

The basis of modern anatomical and functional division is the doctrine of the segmental structure of the liver. Lobes, sectors, segments are usually called areas of the liver of various sizes that have separate blood and lymph circulation, innervation and outflow of bile. The portal vein, hepatic artery, bile ducts and hepatic veins branch in the liver. The course of the branches of the portal vein, hepatic artery and bile duct within the organ is relatively identical. These vessels and bile ducts are usually called the Glissonian, or portal, system, in contrast to the hepatic veins, which are called the caval system. Segmental division of the liver is carried out along the portal and caval systems. Division of the liver according to the portal system is more often used in surgical practice, as it has more anatomical justifications.

The intrahepatic architecture of the portal vein underlies most segmental division patterns (Fig. 2). The classification of S. Couinaud (1957) has become widespread, according to which the liver is divided into 2 lobes - right and left, 5 sectors and 8 most constantly occurring segments. The segments, grouped along radii around the gate of the liver, are included in larger independent sections of the organ, called sectors. Thus, segments III and IV form the left paramedian sector. The left lateral sector (monosegmental includes only segment II, and the right paramedian sector includes segments V and VIII, the right lateral sector includes segments VI and VII; segment I is the dorsal sector (monosegmental). Each lobe, sector or segment of the liver has in most cases, the so-called Glissonian pedicle, accessible to surgical treatment, in which, closely adjacent to each other, are located the branches of the portal vein, hepatic artery and hepatic duct, covered with a connective tissue membrane.

Blood vessels

Blood enters the liver from the portal vein and hepatic artery; 2/3 of the blood volume enters through the portal vein and only 1/3 through the hepatic artery. However, the importance of the hepatic artery for the functioning of the liver is great, since arterial blood is rich in oxygen.

Arterial blood supply to the liver carried out from the common hepatic artery (a. hepatica communis), which is a branch of the truncus coeliacus. Its length is 3 - 4 cm, diameter 0.5 - 0.8 cm. The hepatic artery directly above the pylorus, not reaching 1-2 cm from the common bile duct, is divided into a. gastroduodenalis and a. hepatica propria. The proper hepatic artery (a. hepatica propria) passes upward in the hepatoduodenal ligament, while it is located to the left and somewhat deeper than the common bile duct and in front of the portal vein. Its length ranges from 0.5 to 3 cm, diameter from 0.3 to 0.6 cm. The proper hepatic artery in its initial section gives off a branch - the right gastric artery and, before entering the gate of the liver or directly at the gate, is divided into the right and left branch. In some cases, a branch arises from the hepatic artery - the quadrate lobe of the liver. Typically, the left hepatic artery supplies the left, quadrate, and caudal lobes of the liver.

Right hepatic artery supplies mainly the right lobe of the liver and gives an artery to the gallbladder.

Arterial anastomoses of the liver are divided into two systems: extraorgan and intraorgan. The extraorgan system is formed mainly by branches extending from a. hepatica communis, aa. gastroduodenalis and hepatica dextra. The intraorgan collateral system is formed through anastomoses between the branches of the liver's own artery.

Venous system of the liver represented by afferent and efferent veins. The main afferent vein is the portal vein. The outflow of blood from the liver occurs through the hepatic veins, which flow into the inferior vena cava.

Portal vein(vena portae) is most often formed from two large trunks: the splenic vein (v. lienalis) and the superior mesenteric vein (v. mesenterica superior).

Rice. 2. Scheme of segmental division of the liver: A - diaphragmatic surface; B - visceral surface; B - segmental branches of the portal vein (projection on the visceral surface). I - VIII - liver segments, 1 - right lobe; 2 - left lobe.

The largest tributaries are the gastric veins (v. gastrica sinistra, v. gastrica dextra, v. prepylorica) and the inferior mesenteric vein (v. mesenterica inferior) (Fig. 3). The portal vein most often begins at the level of the second lumbar vertebra behind the head of the pancreas. In some cases, it is located partially or completely within the parenchyma of the gland, has a length of 6 to 8 cm, a diameter of up to 1.2 cm, and has no valves. At the level of the portal of the liver v. portae is divided into the right branch, which supplies the right lobe of the liver, and the left branch, which supplies the left, caudal and quadrate lobes.

Portal vein connected by numerous anastomoses with the vena cava (portocaval anastomosis). These are anastomoses with the veins of the esophagus and the veins of the stomach, rectum, periumbilical veins and veins of the anterior abdominal wall, as well as anastomoses between the roots of the veins of the portal system (superior and inferior mesenteric, splenic, etc.) and the veins of the retroperitoneal space (renal, adrenal, testicular veins or ovary, etc.). Anastomoses play an important role in the development of collateral circulation in case of outflow disorders in the portal vein system.

Portocaval anastomoses are especially well expressed in the rectal area, where the v. rectalis superior, flowing into v. mesenterica inferior, and vv. rectalis media et inferior, related to the inferior vena cava system. On the anterior abdominal wall there is a pronounced connection between the portal and caval systems through vv. paraumbilicales. In the area of ​​the esophagus through connections v. gastrica sinistra and v.v. oesophagea an anastomosis of the portal vein with v. is created. azygos, i.e., the system of the superior vena cava (Fig. 4).

Hepatic veins(v.v.hepaticae) are the efferent vascular system of the liver. In most cases there are three veins; right, middle and left, but their number can greatly increase, reaching 25. The hepatic veins drain into the inferior vena cava below where it passes through the opening in the tendinous part of the diaphragm into the chest cavity.

Rice. 3. Portal vein and its large branches (according to L. Schiff). P - portal vein; C - gastric vein; IM - inferior mesenteric vein; S - splenic vein; SM - superior mesenteric vein.

In most cases, the inferior vena cava passes through the posterior part of the liver and is surrounded by parenchyma on all sides.

Portal hemodynamics characterized by a gradual drop from high pressure in the mesenteric arteries to the lowest level in the hepatic veins. It is important that the blood passes through two capillary systems: the capillaries of the abdominal organs and the sinusoidal bed of the liver. Both capillary networks are connected to each other by the portal vein.

Blood of the mesenteric arteries under a pressure of 120 mm Hg. Art. enters the network of capillaries of the intestines, stomach, and pancreas. The pressure in the capillaries of this network is 15 - 10 mm Hg. Art. From this network, blood enters the venules and veins that form the portal vein, where normally the pressure does not exceed 10 - 5 mm Hg. Art. From the portal vein, blood is directed into the interlobular capillaries, from there it enters the hepatic venous system and passes into the inferior vena cava. The pressure in the hepatic veins ranges from 5 mm Hg. Art. to zero.

Thus, the pressure drop in the portal bed is 120 mmHg. Art. Blood flow may increase or decrease with changes in pressure gradient. G. S. Magnitsky (1976) emphasizes that portal blood flow depends not only on the pressure gradient, but also on the hydromechanical resistance of the portal vessels, the value of which is determined by the total resistance of the first and second capillary systems. A change in resistance at the level of at least one capillary system leads to a change in the total resistance and an increase or decrease in portal blood flow. It is important to emphasize that the pressure drop in the first capillary network is 110 mmHg. Art., and in the second - only 10 mm Hg. Art. Consequently, the main role in changing portal blood flow is played by the capillary system of the abdominal organs, which is a powerful physiological tap. Significant fluctuations in hydromechanical resistance occur as a result of changes in the lumen of blood vessels under the influence of nervous and humoral regulation. Through the portal bed in humans, blood flows at an average speed of 1.5 l/min, which corresponds to 1/3 of the IOC.

Liver histotopography

Liver It is a mass of liver cells penetrated by blood sinusoids. According to modern concepts, hepatocytes form anastomosing plates from one row of cells that are in close contact with the branched blood labyrinth of the sinusoids (Fig. 5). Since 1883, the main morphophysiological unit of the liver has been considered a “classical” hexagonal lobule; its center is the hepatic vein - the initial link of the venous system that collects blood flowing from the liver. The parenchyma of the lobules is formed by radially located hepatic beams; these are plate-like formations one cell thick. The lobules are separated from each other by layers of connective tissue called portal fields associated with the fibrous capsule of the liver.

Rice. 4. Portocaval anastomoses (according to B V Petrovsky): 1 - portocaval anastomoses in the rectal area 2 - anastomoses in the esophagus. 3 - anastomoses in the stomach, IVC - inferior vena cava. PV - portal vein

The interlobular connective tissue of a normal liver is poorly developed. The portal fields contain branches of the portal vein, hepatic artery, bile and lymphatic canaliculi. Penetrating through the terminal plate of hepatocytes, which separates the parenchyma of the lobules from the portal field, the portal vein and hepatic artery give their blood to the sinusoids. The sinusoids drain into the central vein of the lobule. The diameter of the sinusoids ranges from 4 to 25 microns, depending on the functional state of the liver. At the point where the venule flows into the sinusoid and the sinusoid into the hepatic vein, there are external and internal smooth muscle sphincters that regulate blood flow into the lobule. The hepatic arteries, like the corresponding veins, break up into capillaries. They enter the liver lobule and, at its periphery, merge with capillaries originating from the portal veins. Due to this, blood coming from the portal vein and the hepatic artery mixes in the intralobular capillary network (Fig. 6).

Rice. 5. Reconstruction of a liver fragment according to N. Elias

There is another point of view, according to which the secretory lobule or an acinar unit similar to it is taken as a morphophysiological unit. The liver parenchyma is functionally divided into small areas with a portal field in the center, limited by the central veins of two adjacent hepatic lobules, 3-4 such fragments of parenchyma form a complex acinus or portal lobule with a vascular bundle of the portal tract in the center and hepatic veins lying in three corners on the periphery .

Intralobular sinusoids, representing the microvasculature of the circulatory system of the liver, are in direct contact with each hepatocyte. The unique structure of the walls of the hepatic sinusoids contributes to the maximum exchange between the bloodstream and the hepatic parenchyma. The wall of the liver sinusoids does not have the basement membrane characteristic of the capillaries of other organs and is built from a single row of endothelial cells. Between the endothelial cells and the surface of the liver cells there is a free perisinusoidal space - the space of Disse. It has been established that the surface of endothelial cells is covered with a substance of mucopolysaccharide nature, which also fills the cellular pores of Kupffer cells, intercellular gaps and spaces of the DNA. This substance carries out intermediary exchange between blood and liver cells. The functionally active surface of liver cells increases significantly due to numerous tiny outgrowths of the cytoplasm - microvilli.

Rice. 6. 1 - portal vein; 2 - hepatic artery; 3 - sinusoids; 4 - internal sphincter; 5 - central vein; 6 - external sphincter; 7 - arteriole.

Endothelial cells, depending on their functional state, are divided into endothelial cells themselves, which perform a support function, active endothelial cells (Kupffer cells), which have a phagocytic function, and fibroplastic cells, which participate in the formation of connective tissue. Histochemical examination in the cytoplasm of Kupffer cells reveals an increased content of RNA, PAS-positive granules, and high activity of acid phosphatase.

The connective tissue of the portal fields, along with the portal triad, including branches of the portal vein, hepatic artery and interlobular bile ducts, contains single lymphocytes, histiocytes, plasma cells and fibroblasts. The connective tissue of the portal tracts is represented by collagen fibers, clearly visible when stained with picrofuchsin or the three-color Mallory method.

Biliary system

Its initial link is the intercellular bile canaliculi (capillaries), formed by the biliary poles of two or more adjacent hepatocytes (Fig. 7). Bile canaliculi do not have their own wall; they are formed by the cytoplasmic membranes of hepatocytes. Histological examination does not reveal bile canaliculi, but is clearly visible in the reaction to alkaline phosphatase. Intercellular bile canaliculi, merging with each other at the periphery of the hepatic lobule, form larger perilobular bile ducts (terminal ductules, cholangioles). Cholangioles are formed by cuboidal epithelial cells. During electron microscopic examination, microvilli are visible on the surface of the epithelial cells of the cholangioles. Passing through the terminal plate of hepatocytes, in the periportal zone the cholangioles flow into the interlobular bile ducts (ducts, cholangae). The walls of these ducts are formed by connective tissue; in larger ducts there is also a layer of smooth muscle fibers.

Rice. 7. Intrahepatic bile ducts (according to N. Popper, F. Schaffner). 1 - liver cell; 2 - Kupffer cell; 3 - sinusoid; 4 - intercellular bile canaliculus; 5 - perilobular bile duct; b - interlobular bile duct; 7 - vein; 8 - lymphatic vessel.

Rice. 8. Extrahepatic bile ducts. 1 - gallbladder; 2- - ductus cysticus; 3 - ductus hepaticus; 4 - ductus choledochus; 5 - ductus pancreaticus; 6 - sphincter Oddi.

On the lower surface of the liver, in the region of the transverse groove, the left and right bile ducts join to form the common hepatic duct. The latter, merging with the cystic duct, flows into the common bile duct, 8–12 cm long. The common bile duct opens into the lumen of the duodenum in the area of ​​the major duodenal papilla. The distal end of the common bile duct is dilated, in its wall there is a layer of smooth muscle - the sphincter (Fig. 8),

Ultrastructure of hepatocyte

Upon electron microscopic examination, the hepatocyte has an irregular hexagonal shape with unclearly defined angles.

There is a sinusoidal pole facing the blood sinusoid and a biliary pole facing the bile canaliculus (Fig. 9). The cytoplasmic membrane of the hepatocyte consists of outer and inner layers, between them there is an osmiophobic layer 2.5 - 3.0 nm wide. The membrane has pores that provide communication between the endoplasmic reticulum and the extracellular environment. Numerous membrane outgrowths - microvilli - are especially clearly expressed at the sinusoidal pole of the hepatocyte; they increase the functionally active area of ​​the hepatocyte. Numerous metabolites are captured by the villi of the sinusoidal pole, and secretion is carried out at the biliary pole of the hepatocyte. These processes are regulated by enzyme systems, in particular alkaline phosphatase and ATPase. Hyaloplasm, the main substance of the cytoplasm of hepatocytes, is weakly osmiophilic, with vaguely defined small granules, vesicles and fibrils. Soluble components of the cytoplasmic matrix include a significant amount of protein, a small amount of RNA and lipids, enzymes of glycolysis, transamination, etc. The hyaloplasm contains cytoplasmic organelles and inclusions. Core. Round and light, it is located in the central part of the hepatocyte, has a clearly visible nuclear envelope, a few small clumps of chromatin and from 1 to 4 round oxyphilic nucleoli. In rare cases, hepatocytes contain two nuclei.

The nuclear envelope in hepatocytes is closely connected with the endoplasmic reticulum: direct transitions of the outer membrane of the nuclear envelope into the membranes of the endoplasmic reticulum and communication of the slit-like space between the membranes of the nuclear envelope with the tubules of the granular endoplasmic reticulum are observed. DNA and histones in the form of a deoxyribonucleoprotein complex, acidic proteins, rRNA, and mRNA are localized in the chromatin of the nucleus. Numerous enzymes involved in the synthesis of RNA, DNA and protein are found in the hepatocyte nucleus.

The endoplasmic reticulum of the hepatocyte is represented by a system of tubules and cisterns formed by parallel membranes. The endoplasmic reticulum consists of two parts: granular (granular) and smooth. Under physiological conditions, the granular part is much more developed than the smooth part; it is located mainly around the nucleus and mitochondria; on its outer membrane there are numerous osmiophilic granules with a diameter of 12 - 15 nm - ribosomes. The membranes of the smooth endoplasmic reticulum are located near the biliary pole of the hepatocyte, where the synthesis of glyco- and lipoproteins, glycogen, and cholesterol occurs. Both parts of the endoplasmic reticulum are closely interconnected, representing a system of continuous tubes. The physiological role of the endoplasmic reticulum is the neutralization of medicinal and toxic substances, conjugation of bilirubin, metabolism of steroids, biosynthesis of proteins secreted by the cell into the tissue fluid, and direct participation in carbohydrate metabolism.

Rice. 9. Scheme of the ultrastructure of a hepatocyte (I), Kupffer cell (II), bile-epithelial cell (III) (according to A.F. Blyuger). 1 - core; 2 - nucleolus; 3 - nuclear membrane; 4 - rough endoplasmic reticulum; 5 - smooth endoplasmic reticulum; 6 - mitochondria; 7 - Golgi complex; 8 - lysosomes; 9 - polyribosomes; 10 - ribosomes; II - microtubule; 12 - desmosome; 13 - vacuole; 14 - space of Disse; 15 - bile canaliculus; 16 - peroxisome; 17 - pinocytotic vesicles; 18 - sinusoids", 19 - lipids; 20 - basement membrane: 21 - microvilli; 22 - glycogen; 23 - interlobular bile duct; 24 - centriole.

Golgi apparatus, or lamellar complex, consists of double membranes forming flattened sacs and small vesicles. It is usually located in close proximity to the smooth endoplasmic reticulum at the biliary pole of the hepatocyte. The functional purpose of the Golgi apparatus is determined by its important role in secretory processes. Depending on the phase of bile secretion, the components of the Golgi apparatus change. Its participation in the formation of lysosomes and glycogen is assumed.

In the cytoplasm of hepatocytes, in close topographic contact with the tubular system described above, there are granular formations: mitochondria, lysosomes, microbodies.

Mitochondria have very variable shape and location in the cell depending on its location in the lobule or the characteristics of the functional state. Typically, mitochondria are round, oval or elongated, surrounded by a three-layer membrane. The inner layer of membranes forms membrane partitions - cristae, on which granular particles are located. Oxidative phosphorylation occurs in granular particles. The mitochondrial matrix has a fine-grained structure, containing RNA granules, thin strands of DNA and single lipid inclusions. The most important enzyme systems are localized in mitochondria; the central place among them is occupied by the enzymes of the Krebs cycle, deamination and transamination enzymes.

Lysosomes They have a round or ellipsoidal shape, surrounded by a single-layer lipoprotein membrane. Lysosomes are usually localized at the biliary pole of the hepatocyte, and therefore they are called peribiliary bodies. The greatest number of lysosomes are contained in the peripheral zones of the hepatic lobule. Lysosomes are considered as an apparatus for intracellular digestion and are divided into primary, which have not yet used their lytic enzymes, and secondary, in which contact between hydrolases and the substrate has already occurred. Secondary lysosomes are divided into digestive vacuoles, which carry out the lysis of exogenous substances that enter the cell through pinocytosis and phagocytosis, autophagy vacuoles, which carry out the lysis of endogenous material, and residual bodies, or segrosomes, containing compact material in which the breakdown of the substrate is completed. The function of lysosomes can be defined as “intracellular digestion”; they participate in protective reactions, the formation of bile, and ensure intracellular homeostasis. In addition to organelles, the cytoplasm of hepatocytes contains various inclusions: glycogen, lipids, pigments, lipofuscins.

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Table of contents of the topic "Topographic anatomy of the liver.":

Portal vein, v. portae, also brings blood to the liver. It collects blood from all unpaired abdominal organs. Portal vein formed from the fusion of the superior mesenteric, v. mesenterica superior, and splenic, v. splenica (lienalis), veins. The place of their confluence, that is, the place of formation of v. portae. located behind the head of the pancreas.

They drain into the portal vein v. pancreaticoduodenalis superior, v. prepylorica and right and left gastric veins, vv. gastricae dextra et sinistra. The latter often flows into the splenic vein. Inferior mesenteric vein, v. mesenterica inferior, as a rule, flows into the splenic vein, less often into the superior mesenteric vein.

From under the head of the pancreas portal vein goes up behind the duodenum and enters the space between the layers of the hepatoduodenal ligament. There it is located behind the hepatic artery and common bile duct. The length of the portal vein ranges from 2 to 8 cm.

At a distance of 1.0-1.5 cm from porta hepatis or at the gate it divides into right and left branches, r. dexter et r. sinister.

Tumors of the pancreas, especially its head, can compress the pancreas lying posterior to the head portal vein, resulting in portal hypertension, that is, an increase in venous pressure in the portal vein system.

Outflow through the portal vein is also impaired in liver cirrhosis. A compensatory mechanism for impaired outflow becomes collateral blood flow through anastomoses with branches of the vena cava ( portocaval anastomoses).

Portocaval anastomoses are:
1) anastomoses between the veins of the stomach (system v. portae) and the veins of the esophagus (system v. cava superior);
2) anastomoses between the upper (v. portae) and middle (v. cava inferior) veins of the rectum;
3) between the umbilical veins (v. portae) and the veins of the anterior abdominal wall (v. cava superior and inferior);
4) anastomoses of the superior and inferior mesenteric, splenic veins (v. portae) with veins of the retroperitoneal space (renal, adrenal, testicular or ovarian veins and others flowing into v. cava inferior).

Hepatic veins

Hepatic veins,vv. hepaticae, drain blood from the liver. In most cases, there are three constantly occurring venous trunks: the right, intermediate and left hepatic veins. They flow into the inferior vena cava immediately below foramen v. cavae in the tendon part of the diaphragm. On the pars nuda of the posterior surface of the liver, a groove of the inferior vena cava, sulcus venae cavae, is formed.

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:

Excessive physical activity and pressure fluctuations negatively affect the tone of liver tissue.

• 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.

Humoral

Regulation of this type occurs through hormones, such as:

Hormonal imbalances can negatively impact liver function and integrity.

• Adrenalin. It is produced during stress and affects the α-adrenergic receptors of the portal vessel, causing relaxation of the smooth muscles of the intrahepatic vascular walls and a decrease in pressure in the blood flow system.
• Norepinephrine and angiotensin. They have the same effect on the venous and arterial systems, causing a narrowing of the lumen of their vessels, which leads to a decrease in the amount of blood entering the organ. The process is started by increasing vascular resistance in both channels (venous and arterial).
• Acetylcholine. The hormone helps to expand the lumen of arterial vessels, which means it improves blood supply to the organ. But at the same time, a narrowing of the venules occurs, therefore, the outflow of blood from the liver is disrupted, which provokes the deposition of blood into the hepatic parenchyma and a jump in portal pressure.
• Metabolic products and tissue hormones. Substances dilate arterioles and narrow portal venules. There is a decrease in venous circulation against the background of an increase in the flow rate of arterial blood with an increase in its total volume.
• Other hormones - thyroxine, glucocorticoids, insulin, glucagon. The substances cause an increase in metabolic processes, while blood flow increases against the background of a decrease in portal inflow and an increase in arterial blood supply. There is a theory that adrenaline and tissue metabolites influence these hormones.

Rice. 1. Topography of the liver; 1 - hepar; 2 - lig. falciforme hepatis; 3 - ventriculus; 4 - lien; 5 - colon transversum; 6 - lig. hepatogastricum.

The weight of a human liver reaches 1.5 kg, its consistency is soft, its color is reddish-brown, and its shape resembles a large shell. The convex diaphragmatic surface of the liver (facies diaphragmatica) faces upward and posteriorly. Anteriorly and especially to the left, the liver becomes thinner (Fig. 1 and 2). The lower visceral surface (facies visceralis) is concave. The liver occupies the right hypochondrium and extends through the epigastric region into the left hypochondrium. The anterior pointed edge of the liver usually does not extend from under the right costal arch to the outer edge of the right rectus abdominis muscle. Next, the lower border of the liver passes obliquely to the junction of the cartilages of the VII and VIII left ribs. The liver occupies almost the entire dome of the diaphragm. On the left it comes into contact with the stomach, below - with the right kidney, with the transverse colon and duodenum.

Rice. 2. Liver (top): 1 - lis. triangulare deist.; 2 - diaphragm; 3 - lig. coronarium hepatis; 4 - lig. triangulare sin.; 5 - appendix fibrosa hepatis; 6 - lobus sin. hepatis; 7 - lig. falciforme hepatis; 8 - lig. teres hepatis; 9 - incisura lig. teretis; 10 - margo inf.; 11 - vesica fellea (fundus); 12 - lobus dext. hepatis.
Rice. 3. Liver (back): 1 - lig. triangulare sin.; 2 - impressio gastrica; 3 - lig. coronarium hepatis; 4 - impressio oesophagea; 5 - lig. venosum hepatis; 6 - lobus caudatus hepatis; 7 - lig. falciforme hepatis; 8 - v. hepatica; 9 - lobus dext. hepatis; 10 - v. cava inf.; 11 - lig. v. cavae; 12 - facies diaphragmatica; 13 - impressio suprarenalis; 14 - processus caudatus; 13 - collum vesicae felleae; 16 - lig. triangulare dext.; 17 - impressio renalis; 18 - impressio colica; 19 - impressio duodenalis; 20 - vesica fellea; 21 - ductus choledochus; 22 - v. portae; 23 - lobus quadratus; 24 - lig. falciforme hepatis; 26 - a. hepatica propria; 26 - lig. teres hepatis; 27 - porta hepatis; 28 - tuber omentale; 29 - lobus sin.; 30 - appendix fibrosa hepatis.

The liver, with the exception of the upper-posterior surface attached to the diaphragm, is covered with peritoneum. The transition of the peritoneum from the diaphragm to the liver along the frontal plane is designated as the coronary ligament (lig. coronarium hepatis), the transition along the sagittal plane is designated as the falciform ligament (lig. falciforme hepatis), dividing the diaphragmatic surface of the liver into the right and left lobes (lobus hepatis dexter et sinister ). The visceral surface is divided into right, left, caudate (lobus caudatus) and square (lobus quadratus) lobes by two longitudinal grooves and one transverse one (porta of the liver). The gallbladder (see) is placed in the recess of the right longitudinal groove in front, and the inferior vena cava in the back. The left longitudinal groove includes the round ligament of the liver (lig. teres hepatis), formed from the neglected umbilical vein. Here it passes into the venous ligament (lig. venosum) - the remnant of the overgrown ductus venosus. Under the peritoneum on top of the liver there is a connective tissue capsule.

The portal vein (see) and the hepatic artery entering the gate of the liver and the lymphatic vessels and bile duct exiting the gate (Fig. 3) are covered with layers of peritoneum that make up the hepatoduodenal ligament (lig. hepatoduodenal). Its continuation is the hepatogastric ligament (lig. hepatogastricum) - the lesser omentum. A sheet of peritoneum stretches down to the right kidney from the liver - the hepatorenal ligament (lig. hepatorenale). Between the liver and the diaphragm on the sides of the falciform ligament, the right and left hepatic bursae (bursa hepatica dext. et sin.) are distinguished; between the liver and the stomach behind the lesser omentum is the omental bursa (bursa omentalis). Liver segments are shown in Fig.

The main segments of the liver: I - anterior segment: II - posterior segment; III - medial segment; IV - lateral segment. 1 - ductus cholcdoclius; 2 - v. portae; 3 - a. hepatica.

Rice. 4. Scheme of the structure of the lymphatic vessels of the liver: 1 - retrosternal lymph nodes; 2 - anterior group of diaphragmatic nodes; 3 - posterior group of diaphragmatic nodes; 4 - inferior vena cava; 5 - inferior phrenic artery; b - thoracic aorta; 7 - celiac lymph nodes; 8 - hepatic veins; 9 - hepatic lymph nodes; 10 - deep lymphatic vessels; 11 - superficial lymphatic vessels; 12 - diaphragm.

The bloodstream of the liver consists of the intraorgan part of the venous portal system, the drainage system of the hepatic veins and the system of hepatic arteries. Arterial blood supply to the liver is carried out by the hepatic artery (from the celiac artery system), which, entering the portal of the liver, is divided into right and left branches. Often there are accessory hepatic arteries coming from the branches of the celiac artery and from the superior mesenteric artery. The portal vein brings the bulk of blood to the liver. It is divided into lobar veins, from which segmental veins originate. Continuing to divide, the branches of the portal vein first become interlobular, and then thin septal venules, turning into capillaries - sinusoids of the lobule. The septal arterioles also open here, completing the branching of the segmental intrahepatic arteries. Thus, mixed blood flows through the sinusoids. Sinusoids are equipped with devices to regulate blood flow. As a result of the fusion of sinusoids, the central veins of the lobules are formed, from which blood flows first into the sublobular, and then into the collecting veins and, finally, into 3-4 hepatic veins. The latter open into the inferior vena cava. The lymphatic system of the liver (Fig. 4) begins with perilobular and superficial networks of capillaries, folding into superficial and deep lymphatic vessels, through which lymph flows either to the lymph nodes at the porta hepatis, or to the subphrenic nodes around the inferior vena cava. The vagus nerves and branches of the solar plexus take part in the innervation of the liver, thanks to which autonomic and afferent innervation is provided.

See also Portal circulation.

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The hepatic mass fills the right dome of the diaphragm and extends to the left of the body midline below the heart (Fig. 1 A). The most typical shape of the anterior surface of the liver, namely its decreasing volume to the left of the falciform ligament, is very convenient for laparoscopic access to extrahepatic biliary structures. The apex of the lateral segment of the left lobe of the liver may have the form of a fibrous continuation, which is an embryonic remnant (Fig. 1 B). Less common is enlargement of the right lobe of the liver downwards, which may cause additional difficulties (Fig. 1 B). The edge of the liver is directed from above to the left and below to the right, leaving part of the anterior wall of the stomach and pylorus open on the left and the proximal part of the transverse colon on the right. The tip of an unchanged gallbladder may protrude between the colon and the lower edge of the liver.

When studying the anatomy of the liver in three projections, one must always correlate it with the anatomy of neighboring organs. The relationship between the liver and the diaphragm is determined by the commonality of their embryonic origin - the transverse septum (Fig. 2 A). The areas of the liver not covered by peritoneum are the result of the transition of the parietal peritoneum from the lower surface of the diaphragm to the liver. This feature of the distribution of the peritoneum forms a diamond-shaped crown above the liver, called the coronary ligament.

The border of attachment of the “ligaments” is located on the upper surface of the liver far above and posteriorly, forming a deep suprahepatic pocket on the right. In the center of this area is the confluence of the inferior vena cava with the main hepatic veins. Anteriorly, the coronary ligament passes into the falciform ligament, the head portion of the ventral mesentery. Along the edges, left and right, the anterior and posterior surfaces of the coronary ligament come together at an acute angle and form triangular ligaments.

When the surgeon transects the left triangular ligament to mobilize the lateral segment of the left lobe of the liver, he must be aware of the proximity of the hepatic veins and the inferior vena cava. Access to these vessels, if damaged, will be extremely difficult due to their deep localization. Small veins running from the posterior surface of the liver directly to the inferior vena cava reflect the peculiarity of the evolutionary development of the vena cava from the dorsal part of the venous plexus of the liver. Note the location of the inferior left phrenic vein, which passes along the anterior semicircle of the esophageal opening of the diaphragm. This is a very common anatomy variant.

The organs of the upper floor of the abdominal cavity, when viewed on a CT scan slice, are located in the shape of a kidney or bean (Figure 2 B). The spine and large vessels fill the cavity, and the organs themselves are located posteriorly and to the sides, in the diaphragmatic recesses. The most posterior position is occupied by the kidneys.

In a sagittal section (Fig. 3), the abdominal cavity has a wedge shape due to the slope of the lumbar spine and adjacent lumbar muscles. The hepatorenal volvulus (Morrison's pouch) is the outermost space of the abdominal cavity. To the right and behind, the lower surface of the liver goes around the kidney with perinephric fiber, and in front of it is the hepatic angle of the colon.

A sagittal section of the right upper quadrant of the abdominal cavity (Fig. 4) shows that the inferior vena cava is located in the center of the abdominal cavity, and immediately in front of it is the hepatoduodenal ligament with the portal vein. On a frontal cholangiogram, the common bile duct usually runs along the right edge of the lumbar vertebrae. To view small details without overlapping images of underlying structures, the patient should be turned slightly to the right (Fig. 5).

If the liver is elevated, the hepatogastric omentum becomes visible, another derivative of the ventral mesentery, which extends from the lesser curvature of the stomach to the groove of the venous ligament and the porta hepatis (Fig. 6). The free edge of the omentum surrounds the bile ducts and forms the hepatoduodenal ligament. The place of contact between the anterior surface of the fundus of the stomach and the lower surface of the lateral segment of the left lobe of the liver is also visible. The initial section of the duodenum, previously closed by the edge of the liver, is visible, and the relative position of the intestine and the lower surface of the quadrate lobe, as well as the gallbladder, is visible. And finally, on the right, the relative position of the hepatic angle of the colon, the right lobe of the liver and the gallbladder is open.

When the stomach and duodenum are retracted, the root of the mesentery of the transverse colon and the boundaries of the omental bursa behind the lesser omentum become visible (Fig. 7). In the upper part of the bursa, the caudate lobe of the liver is visible, which is usually of considerable size. The fold of peritoneum between the liver and pancreas has the appearance of a ridge formed by the hepatic artery, passing through the retroperitoneal space of the omental bursa and turning into the hepatoduodenal ligament.

When the posterior layer of the parietal peritoneum is spread apart, the anatomical structures of the porta hepatis and their relationship with the pancreas are exposed (Fig. 8). The trunk of the celiac artery is usually divided into three branches, giving rise to the left gastric artery, hepatic and splenic arteries.

And let’s complete the review of the organs of the upper abdominal cavity with a rear view (Fig. 9). The right lobe of the liver extends posteriorly over the superior pole of the right kidney, so that the right adrenal gland is enclosed between the kidney, liver, and inferior vena cava. The inferior vena cava, for a greater or lesser extent, is located in the fossa separating the right and left lobes of the liver. To the left of the vena cava lies the caudate lobe of the liver.

The gastrohepatic omentum extends from the lesser curvature of the stomach to the hilum of the spleen and the groove of the venous ligament. The esophagus is located immediately to the left of the quadrate lobe, between the lower thoracic aorta posteriorly (behind the crura of the diaphragm) and the lateral segment of the left lobe of the liver anteriorly. The cone-shaped edge of the left lobe protrudes above the cardia of the stomach, reaching the anterior border of the spleen. The fourth section of the duodenum goes obliquely upward between the body of the pancreas in front (removed) and the aorta (removed) behind.

On the lower surface of the liver there is a deep central transverse groove formed by its gate (Fig. 10). The common bile duct, hepatic artery and portal vein - the main anatomical structures of the portal - are adjacent to the right side of the groove, and their branches go to the left side, located for a considerable distance outside the hepatic tissue. The plane drawn along the gall bladder bed and the inferior vena cava mainly separates the left and right lobes of the liver (the caudate lobe extends on both sides).

Near the end of the portal groove on the left side, the round ligament of the liver (a remnant of the umbilical vein) passes through a small depression. The extrahepatic portion of the round ligament below the umbilical notch lies along the free edge of the falciform ligament. From the left end of the portal, a groove of the venous ligament stretches obliquely posteriorly, which runs from the left branch of the portal vein to the inferior vena cava near the diaphragm. The hepatogastric omentum extends from the same groove, continuing to the porta hepatis and surrounding the main portal structures in the form of the hepatoduodenal ligament.

Between the omentum and the inferior vena cava is the caudate lobe of the liver. The caudate and right lobes are connected by a narrow isthmus - the caudate process, lying between the gate and the vena cava. It is the roof of the omental opening connecting the omental bursa and the abdominal cavity. The anterior edge of this opening is the hepatoduodenal ligament, and the posterior edge is the vena cava. The inferior inversion of the parietal peritoneum onto the liver crosses the inferior vena cava immediately inferior to the liver and partially follows the depression of the right adrenal gland on the inferior surface of the right lobe.

It is important for the laparoscopist surgeon to know the segmental structure of the liver (shown in the oblique caudal plane, Fig. 11). Knowledge of the normal anatomy of the bile ducts (which occurs in 70% of cases) is necessary to recognize possible anomalies, identify ductal branches that are not visualized on cholangiograms (due to damage or obstruction), and be more careful about the anatomical structures adjacent to the gallbladder bed. Each biliary segment contains the bile duct, a branch of the portal vein and a branch of the hepatic artery. The hepatic veins run between the segments.

The right and left lobes of the liver are separated by a plane passing through the gall bladder bed and the fossa of the inferior vena cava, and each lobe is divided into two segments. The median hepatic vein is located at the junction of both lobes. The right lobe is divided by an oblique transverse plane, running correspondingly to the right hepatic vein, into anterior and posterior segments. The left hepatic vein divides the left lobe into medial and lateral segments. Each of these large segments consists of an upper and lower part.

The caudate lobe, located behind the upper part of the medial segment, is in contact to varying degrees with both lobes. The terminal sections of the hepatic artery and portal vein are anastomosed with the initial sections of the hepatic vein at the level of the hepatic lobules. Portal vessels and ducts enter each segment from the side of the centrally located gate. The gallbladder bed is formed by the inferior surfaces of the right anterior and left medial segments, and the ducts and vessels passing through these segments are at risk of damage when cholecystectomies are performed.

The cholangiogram shows the normal structure of the biliary system (Fig. 12 A). The right and left hepatic ducts join at the porta hepatis to form the common bile duct (in 90% of cases outside the liver itself). The right hepatic duct is formed by the fusion of the anterior and posterior segmental ducts, which occurs close (~1 cm) to the junction of the right and left hepatic ducts.

The right anterior segmental duct is shorter and located below the posterior segmental duct. The frontal cholangiogram shows that the bifurcation site of the anterior duct is more medial than the posterior duct. In about a third of individuals, there is a subvesical duct, which passes close to the gallbladder bed and drains into the right anterior duct. Unlike other bile ducts, it is not accompanied by a branch of the portal vein. It is not connected to the gallbladder, but can be damaged during cholecystectomy.

The left lateral superior and inferior ducts usually join at or slightly to the right of the left segmental sulcus. Bile flows into the long and thin superior duct from the apex of the left lobe, which passes into the fibrous process. In a small number of people (= 5%), the bile ducts in this appendage may persist and be a source of bile leakage when the appendage is divided to mobilize the left triangular ligament of the liver.

From the upper and lower parts of the medial segment of the left lobe, bile flows into four small ducts. When the medial and lateral segmental ducts join near the porta hepatis, the left hepatic duct is formed. Bile from the caudate part of the medial segment goes in three directions. From the rightmost section, bile usually flows into the right ductal system, from the leftmost section into the left, and from the intermediate section, with approximately equal frequency, into one of the sides.

There are several options for the location of the bile ducts inside the liver. Typically, the main left and right bile ducts join at the center of the porta hepatis (in 10% of cases, within the hepatic parenchyma). In approximately 22% of individuals, the right posterior segmental duct can cross the interlobar fissure and empty into the left hepatic duct (Fig. 12 B).

In 6% of cases, the right anterior segmental duct passes to the left side (Fig. 12 B). If the right segmental ducts are located separately, they may be damaged during cholecystectomy. It is more correct to call these ducts aberrant than accessory, since they collect bile from normal areas of the liver, and are not some kind of additional ones. On the left side, in a quarter of cases, the duct of the medial segment flows into the lower branch of the duct of the lateral segment (Fig. 12 D).

Of the peripheral ducts, the right posterior superior duct has the most consistent location. The remaining subsegmental ducts in 22% of cases have alternative drainage options.

The course of the portal vein trunks when viewed from below corresponds to the segmental structure of the liver (Fig. 13). The portal vein divides outside the liver, near the right side of the portal, and the longer left trunk crosses the portal groove. The right trunk runs close posterior to the infundibular portion of the gallbladder and is most often damaged at this location. The right trunk of the portal vein usually divides into anterior and posterior branches, going to the two main segments of the right lobe in an anterosuperior and posteroinferior direction, respectively. Sometimes this division occurs at the site of the main bifurcation of the portal vein, which thus becomes a trifurcation. During cholecystectomy, the right trunk of the portal vein may be damaged near the porta hepatis.

The left trunk of the portal vein bends anteriorly and enters the liver parenchyma in the region of the groove of the round ligament. It then divides into two branches going to the medial and lateral segments of the left lobe. Each segmental branch feeds the upper and lower sections of its segment. Proximal branches from the main right and left trunks of the portal vein extend to the caudate lobe. Some venous outflow from the gallbladder goes into the right portal trunk, but the main amount of blood flows directly into the hepatic bed of the gallbladder.

Wind G.J.
Applied laparoscopic anatomy: abdominal cavity and pelvis