The concept of the structural unit of the organ. Structural units of the lungs, liver, kidneys, structural features

) under the diaphragm and performing a large number of different physiological functions. The liver is the largest vertebrate gland.

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✪ Anatomy of the liver. Hepatic lobule. The gallbladder.

✪ Why can't our body take a blow to the liver?

✪ Liver structure

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

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The liver is the largest gland in the human body. Its mass is on average 1.5 kg. The liver is located mainly in the right hypochondrium and in the epigastrium. She distinguishes between two surfaces: diaphragmatic and visceral. For a better orientation in the anatomy of the liver, it is necessary to remember several ligaments that are formed when the peritoneum passes from the diaphragm to the liver. The falciform ligament is located in the sagittal plane. The coronary ligament is connected to its posterior edge, which forms extensions on the sides - the right and left triangular ligaments. In the lower free edge of the crescent ligament is the round ligament of the liver. It is an overgrown umbilical vein. From the liver, the hepato-gastric and hepato-duodenal ligaments mentioned in the previous video are also directed, forming the lesser omentum. Anatomically, two large lobes are distinguished in the liver: right and left. The border between them is the sickle and venous ligaments. The latter is an overgrown ductus vein, which in the fetus connects the umbilical vein to the inferior cavity. On the visceral surface of the liver, within its right lobe, two small lobes of the liver are distinguished: square and caudate. The latter has two processes: the caudate and the papillary. On the visceral surface of the liver, you can visually identify a kind of letter H, which is formed due to the special location of the anatomical elements. It consists of: on the right back - the inferior vena cava, on the right in front - the gallbladder, on the left behind - the venous ligament and on the left in front - the round ligament. In the middle, between the listed formations, the gate of the liver is located. They are formed by: the portal vein, hepatic artery and nerves entering the liver, as well as the common hepatic duct and lymphatic vessels leaving the liver. There are 8 segments in the liver. A segment is an area that is supplied with blood by a branch of the third-order portal vein, that is, a segmental vein, and from which the segmental bile duct exits. Various impressions from the abdominal organs can be seen on the liver surface. Outside, the liver is covered with a fibrous capsule, which, in turn, is mesoperitoneally covered by the peritoneum. Connective tissue septa depart from the capsule inside, dividing the liver parenchyma into lobules, which are its structural and functional units. The lobule of the liver has a prismatic shape; it consists of the hepatic beams radially converging towards the center. Each beam consists of hepatic hepatocyte cells. Between these cells, in each beam, are the bile ducts. And between the adjacent beams there are blood sinusoidal capillaries, which converge in the center of the lobule to its central vein. It is worth noting that the sinusoidal capillary is formed by interlobular veins from the portal vein system and interlobular arteries from the hepatic artery system. From the central vein, the blood eventually enters the inferior vena cava. This type of blood circulation is called the miraculous network of the liver. Between adjacent hepatic lobules, the interlobular bile ducts, arteries and veins form the so-called hepatic triad. The already mentioned interlobular ducts, after several branches, are connected to the right and left hepatic ducts. At the gate of the liver, these two ducts join to form a common hepatic duct. Between the leaves of the hepato-duodenal ligament, the common hepatic duct connects with the cystic duct, which departs from the gallbladder, and together they form a common bile duct. That, in turn, goes to the duodenum, in front of which it will connect with the main duct of the pancreas. They both open into the descending part of the duodenum, into its large (or vater) papilla, which at its base contains the sphincter of Oddi. The gallbladder is pear-shaped; bile accumulates and concentrates in it. The gallbladder has 3 parts: the bottom, body and neck. The cystic duct departs from the latter. In relation to the peritoneum, the unfilled gallbladder lies extraperitoneally, and the filled gallbladder - mesoperitoneally.

Liver anatomy

The liver consists of two lobes: right and left. In the right lobe, two more secondary lobes are distinguished: square and caudate. According to the modern segmental scheme proposed by Claude Quineau (1957), the liver is divided into eight segments that form the right and left lobes. The liver segment is a pyramidal area of \u200b\u200bthe hepatic parenchyma, which has a fairly separate blood supply, innervation and outflow of bile. The caudate and square lobes, located behind and in front of the gate of the liver, according to this scheme correspond to S I and S IV of the left lobe. In addition, S II and S III of the liver are isolated in the left lobe, the right lobe is divided into S V - S VIII, numbered around the gate of the liver in a clockwise direction.

The histological structure of the liver

The parenchyma is lobular. The hepatic lobule is a structural and functional unit of the liver. The main structural components of the hepatic lobule are:

hepatic plates (radial rows of hepatocytes);
intralobular sinusoidal hemocapillaries (between the hepatic beams);
bile capillaries (Latin ductuli beliferi) inside the hepatic tracts, between two layers of hepatocytes;
(expansion of the bile capillaries when they leave the lobule);
perisinusoidal space of Disse (slit-like space between the hepatic tracts and sinusoidal hemocapillaries);
central vein (formed by the fusion of intralobular sinusoidal hemocapillaries).

Aspergillus infects almost all food products, but plant products made from cereals, legumes and oilseeds such as peanuts, rice, corn, peas, sunflower seeds, etc. are the basis. - the strongest intoxication, accompanied by acute toxic hepatitis. With a sufficiently long use of contaminated food, chronic aflatoxicosis occurs, in which hepatocellular carcinoma develops in almost 100% of cases.

Hemangiomas of the liver - abnormalities in the development of blood vessels in the liver.
The main symptoms of hemangioma:

heaviness and a 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 fast-onset feeling of fullness and discomfort in the abdomen after eating;
weakness;
excessive sweating;
loss of appetite, at times nausea;
shortness of breath, dyspeptic symptoms;
jaundice.

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.

Liver regeneration

The liver is one of the few organs capable of regaining its original size even when only 25% of normal tissue is retained. In fact, regeneration occurs, but very slowly, and the rapid return of the liver to its original size is more likely due to an increase in the volume of the remaining cells.

In the mature liver of humans and other mammals, four varieties of liver stem / progenitor cells have been found - the so-called oval cells, small hepatocytes, liver epithelial cells, and mesenchymal-like cells.

Oval cells in rat liver were discovered in the mid-1980s. The origin of the oval cells is unclear. Perhaps they come from the cellular populations of the bone marrow, but this fact is being questioned. Mass production of oval cells occurs with various liver lesions. For example, a significant increase in the number of oval cells was observed in patients with chronic hepatitis C, hemochromatosis, alcoholic liver poisoning and directly correlates with the severity of liver damage. In adult rodents, oval cells are activated for subsequent reproduction when replication of the hepatocytes themselves is blocked. The ability of oval cells to differentiate into hepatocytes and cholangiocytes (bipotential differentiation) has been shown in several studies. The ability to support the multiplication of these cells in vitro has also been shown. Recently, oval cells capable of bipotential differentiation and clonal expansion in vitro and in vivo have been isolated from the liver of adult mice. These cells expressed cytokeratin-19 and other surface markers of liver progenitor cells and, when transplanted into an immunodeficient strain of mice, induced the regeneration of this organ.

Small hepatocytes were first described and isolated by Mitaka et al. from the nonparenchymal fraction of rat liver in 1995. Small hepatocytes from the liver of rats with artificial (chemically induced) liver damage or with partial removal of the liver (hepatotectomy) can be isolated by differential centrifugation. These cells are smaller than normal hepatocytes and can multiply and transform into mature hepatocytes in vitro. It has been shown that small hepatocytes express typical markers of hepatic progenitor cells - alpha-fetoprotein and cytokeratins (CK7, CK8 and CK18), which indicates their theoretical ability for bipotential differentiation. The regenerative potential of rat small hepatocytes was tested in animal models with artificially induced liver damage: the introduction of these cells into the portal vein in animals caused the induction of repair in various parts of the liver with the appearance of mature hepatocytes.

A population of liver epithelial cells was first discovered in adult rats in 1984. These cells have a repertoire of surface markers that overlaps, but is somewhat different from the phenotype of hepatocytes and ductal cells. The transplantation of epithelial cells into the liver of rats led to the formation of hepatocytes expressing typical hepatocyte markers - albumin, alpha-1-antitrypsin, tyrosine transaminase and transferrin. Recently, this population of progenitor cells has been found in an adult. Epithelial cells phenotypically differ from oval cells and can differentiate in vitro into hepatocyte-like cells. Experiments on the transplantation of epithelial cells into the liver of SCID mice (with congenital immunodeficiency) showed the ability of these cells to differentiate into hepacites expressing albumin one month after transplantation.

Mesenchymal cells have also been obtained from mature human liver. Like mesenchymal stem cells (MSCs), these cells have a high proliferative potential. Along with mesenchymal markers (vimentin, alpha-smooth muscle actin) and stem cell markers (Thy-1, CD34), these cells express hepatocyte markers (albumin, CYP3A4, glutathione transferase, CK18) and ductal cell markers (CK19). When transplanted into the liver of immunodeficient mice, they form mesenchymal-like functional islets of human liver tissue that produce human albumin, prealbumin and alpha-fetoprotein.

Further studies of properties, cultivation conditions and specific markers of mature liver progenitor cells are required to assess their regenerative potential and clinical use.

Liver transplant

The first liver transplant in the world was performed by the American transplantologist Thomas Starles in 1963 in Dallas. Later, Starles organized the world's first transplant center in Pittsburgh (USA), now bearing his name. By the end of the 1980s, more than 500 liver transplants were performed annually in Pittsburgh under the leadership of T. Starsle. The first in Europe (and the second in the world) medical center for liver transplantation was established in 1967 in Cambridge (Great Britain). It was led by Roy Kaln.

With the improvement of surgical methods of transplantation, the opening of new transplant centers and conditions for the storage and transportation of the transplanted liver, the number of liver transplant operations has steadily increased. If in 1997 in the world up to 8000 liver transplants were performed annually, now this number has increased to 11000, with the United States accounting for more than 6000 transplants and up to 4000 in Western European countries (Table). Among European countries, Germany, Great Britain, France, Spain and Italy play a leading role in liver transplantation.

There are currently 106 liver transplant centers in the United States. 141 centers have been organized in Europe, including 27 in France, 25 in Spain, 22 in Germany and Italy, and 7 in the UK.

Despite the fact that the world's first experimental liver transplant was performed in the Soviet Union by the founder of world transplantation V.P. Demikhov in 1948, this operation was introduced into clinical practice in the country only in 1990.In 1990, the USSR had no more than 70 liver transplants have been performed. Now in Russia, regular liver transplant operations are carried out in four medical centers, including three Moscow ones (Moscow Center for Liver Transplantation, N.V. Sklifosovsky Research Institute for Emergency Medicine, Academician V.I.Shumakov Research Institute of Transplantology and Artificial Organs, Russian Scientific Center for Surgery named after Academician B.V. Petrovsky) and the Central Research Institute of Roszdrav in St. Petersburg. Recently, liver transplants have been carried out in Yekaterinburg (Regional Clinical Hospital No. 1), Nizhny Novgorod, Belgorod and Samara.

Despite the constant growth in the number of liver transplant operations, the annual need for transplantation of this vital organ is satisfied by an average of 50% (table). The incidence of liver transplants in the leading countries ranges from 7.1 to 18.2 operations per million population. The real need for such operations is now estimated at 50 per 1 million of the population.

The first human liver transplant surgeries did not bring much success, as the recipients usually died within the first year after the operation due to transplant rejection and the development of severe complications. The use of new surgical techniques (cavocaval shunting and others) and the emergence of a new immunosuppressant - cyclosporin A - contributed to an exponential increase in the number of liver transplants. Cyclosporin A was first successfully used in liver transplantation by T. Starzlom in 1980, and its widespread clinical use was allowed in 1983. Thanks to various innovations, the postoperative life expectancy was significantly increased. According to the United Network for Organ Sharing (UNOS), the current survival rate of liver transplant patients is 85-90% one year after surgery and 75-85% five years later. It is predicted that 58% of recipients have a chance of living to 15 years.

Liver transplantation is the only definitive treatment for patients with irreversible, progressive liver damage when no other alternative treatment is available. The main indication for liver transplantation is the presence of chronic diffuse liver disease with a life expectancy of less than 12 months, provided that conservative therapy and palliative surgical treatment methods are ineffective. The most common cause of liver transplants is cirrhosis of the liver caused by chronic alcoholism, viral hepatitis C, and autoimmune hepatitis (primary biliary cirrhosis). Less common indications for transplantation include irreversible liver damage due to viral hepatitis B and D, drug and toxic poisoning, secondary biliary cirrhosis, congenital liver fibrosis, cystic liver fibrosis, hereditary metabolic diseases (Wilson-Konovalov disease, Reye's syndrome, alpha-1 deficiency - antitrypsin, tyrosinemia, glycogenosis type 1 and type 4, Neumann-Pick disease, Crigler-Nayyar syndrome, familial hypercholesterolemia, etc.).

Liver transplant is a very expensive medical procedure. According to UNOS, the required costs for inpatient care and patient preparation for surgery, payment of medical staff, removal and transportation of donor liver, surgery and postoperative procedures during the first year are $ 314,600, and for follow-up and therapy - up to $ 21,900 per year. ... For comparison, in the United States the cost of similar costs for a single heart transplant in 2007 was $ 658,800, lung - $ 399,000, kidney - $ 246,000.

Thus, there is a chronic shortage of donor organs available for transplantation, the length of time to wait for surgery (in the United States, the waiting time in 2006 averaged 321 days), the urgency of the operation (the donor liver must be transplanted within 12 hours) and the exceptional cost of traditional liver transplantation. create the necessary prerequisites for finding alternative, more economical and effective strategies for liver transplantation.

Currently, the most promising method of liver transplantation is living donor liver transplant (LIVT)... It is more effective, simpler, safer and much cheaper than the classic cadaveric liver transplantation, both whole and split. The essence of the method is that the left lobe (2, 3, sometimes 4 segments) of the liver is removed from the donor, today it is often endoscopically, that is, less traumatic. TPZD provided a very important opportunity related donation - when the donor is a relative of the recipient, which greatly simplifies both administrative problems and the selection of tissue compatibility. At the same time, thanks to a powerful regeneration system, after 4-6 months, the donor's liver completely restores its mass. The donor liver lobe is transplanted to the recipient either orthotopically, with the removal of the own liver, or, less often, heterotopically, leaving the recipient's liver. At the same time, naturally, the donor organ is practically not exposed to hypoxia, since the operations of the donor and recipient are performed in the same operating room and simultaneously.

Bioengineered liver

A bioengineered liver, similar in structure and properties to a natural organ, has yet to be created, but active work in this direction is already underway.

For example, in October 2010, American researchers from the Institute of Regenerative Medicine at the Wake Forest University Medical Center (Winston-Salem, North Carolina) developed a bioengineered liver organoid grown on the basis of a bio-scaffold from natural ECM from cultures of liver progenitor and endothelial cells. human cells. The liver bioframework with the vascular system preserved after decellularization was colonized with populations of progenitor cells and endothelial cells through the portal vein. After incubation of the bioscaffold for a week in a special bioreactor with continuous circulation of the nutrient medium, the formation of liver tissue with the phenotype and metabolic characteristics of the human liver was noted. In 2013, the Russian Ministry of Defense developed a technical assignment for a prototype of a bioengineered liver.

In March 2016, scientists at Yokohama University managed to create a liver that can replace a human organ. Clinical trials are expected to take place in 2019.

Liver in culture

In Russian there is an expression "sit in the livers", which means very much to bother or annoy someone.

In the Lezgi language, one word is used to designate an eagle and a liver - "lek". This is due to the long-standing custom of the mountaineers to expose the bodies of the dead to be eaten by predatory eagles, who first of all tried to get to the liver of the deceased. Therefore, the Lezgins believed that it was in the liver that the human soul was contained, which now passed into the body of a bird. There is a version that the ancient Greek myth of Prometheus, whom the gods chained to a rock, and an eagle pecked at his liver every day, is an allegorical description of such a burial ceremony for the mountaineers.

The circulatory system of the liver can be divided into a blood flow system, represented by two vessels: the hepatic artery, which carries oxygenated blood and the portal vein, which carries blood from the unpaired organs of the abdominal cavity, these vessels branch into lobar, lobar into segmental, segmental into interlobular, interlobular to the around-lobular artery and vein, from which the capillaries merge on the periphery of the lobules, to the intralobular sinusoidal capillary: mixed blood flows in it, and it itself represents the blood circulation system and flows into the central vein, from which the blood outflow system begins. The central vein continues into the sublobular vein, which is otherwise called the collecting vein (or the loner vein). It got this name because it is not accompanied by other vessels. Sublobular veins pass into three four hepatic veins, which flow into the inferior vena cava.

The structural and functional unit of the liver is the hepatic lobule. There are three ideas about the structure of the hepatic lobule:

Classic hepatic lobule

Partal hepatic lobule

Hepatic acinus

The structure of the classic hepatic lobule

It is a 5-6-sided prism, 1.5-2 mm in size, in the center is the central vein, this is a muscleless type vessel, from which the hepatic tracts radiate radially (in the form of rays), which are two rows of hepatocytes or hepatic cells connected to each other with a friend using tight contacts and desmosomes on the contact surfaces of hepatocytes. A hepatocyte is a large polygonal cell. More often 5-6 angular, with one or two rounded nuclei, often polyploid, where euchromatin predominates, and the nuclei themselves are located in the center of the cell. In the oxyphilic cytoplasm, the EPS groups, the Golgi complex, mitochondria and lysosomes also contain lipid and glycogen inclusions.

Functions of hepatocytes:

Secretion of bile, which contains bile pigments (bilirubin, biliverdin) formed in the spleen as a result of the breakdown of hemoglobin, bile acids synthesizing from cholesterol, cholesterol, phospholipids and mineral components

Glycogen synthesis

Synthesis of blood plasma proteins (albumin, fibrinogen, globulin, except for gamma globulin)

Glycoprotein secretion

Metabolism and deactivation of toxic substances

Sinusoidal capillaries are located between the hepatic tracts, to which the hepatocytes face the vascular surface. They are formed by the fusion of capillaries, from around-lobular arteries and veins on the periphery of the lobule. Their wall is formed by endotheleocytes and stellate macrophages (Kupffer cells) located between them, they have an elliptical shape, elongated nuclei, originate from monocytes, are capable of phagocytosis, the basement membrane of the capillary is intermittent and may be absent for a long continuation. Around the capillary is located around the sinusoidal space of Disse, it contains a network of reticular fibers and large granular lymphocytes, which have several names: pit cells, PIT cells, NK cells or normal killer cells, they destroy damaged hepatocytes and secrete factors that contribute to the proliferation of the remaining hepatocytes. Also around the sinusoidal space of Disse are ITO cells or peresunoidal lymphocytes, these are small cells in the cytoplasm, which contain fat droplets that accumulate fat-soluble vitamins A, D, E, K. They also synthesize collagen of the third type, which form reticular fibers. Between the cells of adjacent rows in the beam, there is a blind-starting bile capillary, which does not have its own wall, but is formed by the biliary surfaces of hepatocytes, in it bile moves from the center of the lobule to the periphery. On the periphery of the lobules, bile capillaries pass into around-lobular bile ducts (cholangioli or ductula), their wall is formed by 2-3 cubic chalangiocytes. The chalangioli continue into the interlobular bile ducts. The lobules are separated from each other by thin layers of loose fibrous connective tissue, in which the interlobular triads are located. They are formed by the interlobular bile duct, the wall of which is formed by a single-layer cubic epithelium or chalangioites. An interlobular artery, which is a muscle-type vessel, and therefore has a fairly thick wall, folds of the inner shell, also an interlobular vein is part of the triad, it belongs to the veins of the muscle type with poor development of myocytes. Has a wide lumen and a thin wall. Interlobular connective tissue is clearly visible only on pig liver preparations. In humans, it becomes clearly visible only with cirrhosis of the liver.

Partal hepatic lobule

It has a triangular shape, its center is formed by a triad, and the central veins of three adjacent classical lobules form its apex. The blood supply to the partal lobule comes from the center of the periphery.

Hepatic acinus

It has the shape of a rhombus, in the acute corners of the rhombus (tops) are the central veins of two adjacent classical hepatic lobules, and in one of the obtuse corners of the rhombus is a triad. The blood supply comes from the center of the periphery.

Pancreas

Large, mixed, that is, exo and endocrine glands of the digestive system. It is a parenchymal organ in which there are: head, body and tail. The pancreatic parenchyma develops from the endoderm, while the stroma develops from the mesenchyme. Outside, the pancreas is covered with a connective tissue capsule, from which connective tissue layers, which are otherwise called septa or trabeculae, extend deep into the gland. They divide the parenchyma of the gland into lobules, with 1-2 million lobules. in each lobule there is an exocrine part, which accounts for 97%, the endocrine part is 3%. The structural and functional unit of the exocrine department is the pancreatic acinus. It consists of a secretory section and an intercalary excretory duct. The secretory department is formed by cells of acinocytes, there are 8-12 of them in the secretory department. These cells: large, conical or pyramidal in shape, with their basal part lie on the basement membrane, their rounded nucleus is displaced to the basal pole of the cell. The cytoplasm of the basal part of the cell is basophilic due to the good development of the EPS group, it stains evenly, and therefore it is otherwise called a homogeneous zone, in the apical part of the cells there are oxyphilic granules containing immature enzymes, which are otherwise called zymogens. Also in the apical part is the Golgi complex, and the entire apical part of the cells is called the zymogenic zone. Pancreatic enzymes that are part of pancreatic juice are: trypsin (breaks down proteins), pancreatic lipase and phospholipase (breaks down fats), amylase (breaks down carbohydrates). In most cases, the secretory section is followed by an intercalary excretory duct, the wall of which is formed by one layer of squamous epithelial cells lying on the basement membrane, but in some cases, the intercalated excretory duct is inserted deep into the secretory compartment, forming a second layer of cells in it, which are called centroacinous cells. The inter-acinar excretory ducts follow the intercalated excretory ducts, they flow into the intralobular excretory ducts. The wall of these ducts is formed by a single-layer cubic epithelium. This is followed by the interlobular excretory ducts, which flow into the common excretory duct, opening in the duodenum lumen. The wall of these excretory ducts is formed by a single-layer columnar epithelium, which is surrounded by connective tissue.

The endocrine part of the lobules is represented by pancreatic islets (islets of Largenhans). Each islet is surrounded by a thin capsule of reticular fibers, separating it from the adjacent exocrine part. The islets also contain a large number of fenestrated capillaries. The islets are formed by endocrine cells (insulocytes). All of them are small, light colored cytoplasm, well-developed Golgi complex, less well-developed group of EPS, and contain granules of secretion.

Varieties of endocrinocytes (insulocytes)

In cells - located in the center of the islet, 70% of all cells, have an elongated pyramidal shape and granules stained basophilically, they contain insulin, which ensures the absorption of nutrients by tissues and has a hypoglycemic effect, that is, reduces the level of glucose in the blood.

And the cells are concentrated on the periphery of the Largenhans islet, make up about 20% of the cells, contain granules that stain oxyphilically, and they contain glucagon, a hormone that has a hyperglycemic effect.

D cells - located on the periphery of the islets make up 5-10%, have a pear-shaped or stellate shape and granules containing somatostotin, this substance that inhibits the production of insulin and glucagon, inhibits the synthesis of enzymes by acinocytes.

D1 cells - 1-2%, are concentrated on the periphery of the Largenhans islet, contain granules with a vasointestinal polypeptide, which, being an antagonist of somatostotin, stimulate the release of insulin and glucagon and stimulate the secretion of enzymes by acinocytes, also dilating blood vessels and reducing blood pressure.

PP cells - 2-5%, concentrated on the periphery of the Largenhans islet, contain granules with a pancreatic polypeptide, which stimulates the secretion of gastric and pancreatic juice.

The structural and functional parameters in the liver lobule are characterized by a diurnal rhythm. The hepatocytes that make up the lobule form the hepatic trabeculae or trabeculae, which, anastomosed with each other, are located along the radius and converge to the central vein. Sinusoidal blood capillaries run between the beams, which are at least two rows of hepatic cells. The wall of the sinusoidal capillary is lined with endotheliocytes, which are devoid (over their greater extent) of the basement membrane and contain pores. Numerous stellate macrophages (Kupffer cells) are scattered between the endothelial cells. The third type of cells - perisinusoidal lipocytes, which are small in size, small drops of fat and triangular in shape, are located closer to the perisinusoidal space. The perisinusoidal space or around the sinusoidal space of Disse is a narrow gap between the capillary wall and the hepatocyte. The vascular pole of the hepatocyte has short cytoplasmic outgrowths that lie freely in the Disse space. Inside the trabeculae (beams), between the rows of hepatic cells, there are bile capillaries that do not have their own wall and are a groove formed by the walls of neighboring hepatic cells. The membranes of adjacent hepatocytes adjoin each other and form endplates in this place. Bile capillaries are characterized by a convoluted course and form short lateral sac-shaped branches. In their lumen, numerous short microvilli are seen extending from the biliary pole of hepatocytes. Bile capillaries pass into short tubes - cholangioli, which flow into the interlobular bile ducts. On the periphery of the lobules in the interlobular connective tissue, the liver triads are located: interlobular arteries of the muscle type, interlobular veins of the nonmuscular type and interlobular bile ducts with a single-layer cubic epithelium

Liver functions:

detoxification function;

barrier - protective function;

hematopoietic function;

endocrine function.

Morphofunctional unit of the liver

If patients suffer from oxygen starvation (intoxication, highlands), all destructive processes of hepatocytes are formed in the center of the lobule, which is explained by the blood flow.

Liver regeneration is very high. You can remove a part of the liver and after 2-3 months its mass grows. This is the basis for the removal of part of the pathological changes in the liver, tk. at this place, a regenerate (healthy liver) is formed. Therefore, given that the regenerate is formed in normal liver tissue, we came up with a method of inflicting minor damage. As a result, the efficiency has become very high.

URINARY SYSTEM

Contains the kidneys and urinary tract. Main function– excretory, and also participates in the regulation of water-salt metabolism, well-developed endocrine function, regulates local true blood circulation and erythropoiesis. Both in evolution and in embryogenesis, there are 3 stages of development.

In the beginning it is laid forebear ... From the segmental pedicles of the anterior mesoderm, tubules are formed, the tubules of the proximal sections open as a whole, the distal sections merge and form a mesonephral duct. The pronephros exist up to 2 days, does not function, dissolve, but the mesonephral duct remains.

Then formed primary kidney ... From the segmental legs of the trunk mesoderm, urinary tubules are formed, their proximal parts, together with the blood capillaries, form renal corpuscles - urine is formed in them. The distal portions drain into the mesonephral duct, which grows caudally and opens into the primary intestine.

In the second month of embryogenesis, secondary or final kidney ... Nephrogenic tissue is formed from the unsegmented caudal mesoderm, renal tubules are formed from it, and the proximal tubules are involved in the formation of renal corpuscles. The distal ones grow, from which the tubules of the nephron are formed. From the urogenital sinus behind the mesonephral duct, an outgrowth is formed in the direction of the secondary kidney, from which the urinary tract develops, the epithelium is a multilayer transitional one. The primary kidney and the mesonephral duct are involved in the construction of the reproductive system.

Bud

The outside is covered with a thin connective tissue capsule. The kidney is isolated cortical substance, it contains renal corpuscles and convoluted renal tubules, inside the kidney is located medullain the form of pyramids. The base of the pyramids faces the cortex, and the top of the pyramids opens into the renal calyx. There are about 12 pyramids in total.

The pyramids are composed of direct tubules, from the descending and ascending tubules nephron loopsand collecting ducts... Part of the straight tubules in the cortical substance are arranged in groups and such formations are called brain rays.

The structural and functional unit of the kidney is the nephron; in the kidney prevail cortical nephrons, most of them are located in the cortex and their loops penetrate shallowly into the medulla, the remaining 20% \u200b\u200b- juxtamedullary nephrons... Their renal corpuscles are located deep in the cortex on the border with the medulla, and the loops are deeply embedded in the medulla. In the nephron, the renal corpuscle, the proximal convoluted tubule, the nephron loop and the distal convoluted tubule are isolated.

The proximal and distal sections are built from convoluted tubules, and the loop from straight tubules.

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Digestive system development

The laying of the digestive system is carried out in the early stages of embryogenesis. On the 7-8th day, in the process of development of a fertilized egg from the endoderm in the form of a tube, the primary intestine begins to form, which on the 12th day differentiates into two parts: the intraembryonic (future digestive tract) and the extraembryonic - the yolk sac. At the early stages of formation, the primary intestine is isolated by the oropharyngeal and cloacal membranes, however, already at the 3rd week of intrauterine development, the oropharyngeal membrane melts, and at the 3rd month - the cloacal membrane. Violation of the membrane melting process leads to developmental abnormalities. From the 4th week of embryonic development, sections of the digestive tract are formed:

derivatives of the anterior intestine - the pharynx, esophagus, stomach and part of the duodenum with the anlage of the pancreas and liver;
derivatives of the midgut - the distal part (located farther from the oral membrane) of the duodenum, the jejunum and the ileum;
derivatives of the hindgut - all parts of the colon.

The pancreas is formed from the outgrowths of the anterior intestine. In addition to the glandular parenchyma, pancreatic islets are formed from the epithelial cords. At the 8th week of embryonic development, glucagon is immunochemically determined in alpha cells, and insulin in beta cells by the 12th week. The activity of both types of pancreatic islet cells increases between the 18th and 20th weeks of gestation.

After the baby is born, the growth and development of the gastrointestinal tract continues. In children under 4 years of age, the ascending colon is longer than the descending colon.

The hepatic lobule is a structural and functional unit of the liver. At the moment, along with the classic hepatic lobule, the portal lobule and acinus are also distinguished. This is due to the fact that various centers are conditionally distinguished in the same real-life structures.

Hepatic lobule (Fig. 4). Currently, under the classic hepatic lobule is meant a section of the parenchyma, delimited by more or less pronounced layers of connective tissue. The center of the lobule is the central vein. The lobule contains epithelial hepatic cells - hepatocytes. A hepatocyte is a polygonal cell, it can contain one, two or more nuclei. Along with the usual (diploid) nuclei, there are also larger polyploid nuclei. The cytoplasm contains all organelles of general importance, contains various types of inclusions: glycogen, lipids, pigments. Hepatocytes in the liver lobule are heterogeneous and differ from each other in structure and function depending on which zone of the liver lobule they are located in: central, peripheral or intermediate.

Structurally functional unit of the liver

Inside the trabeculae (beams), between the rows of hepatic cells, there are bile capillaries that do not have their own wall and are a groove formed by the walls of neighboring hepatic cells. The membranes of adjacent hepatocytes adjoin each other and form endplates in this place. The bile capillaries are characterized by a convoluted course and form short lateral sac-like branches. In their lumen, numerous short microvilli are seen extending from the biliary pole of hepatocytes. Bile capillaries pass into short tubes - cholangioli, which flow into the interlobular bile ducts. On the periphery of the lobules in the interlobular connective tissue, the liver triads are located: interlobular arteries of the muscle type, interlobular veins of the nonmuscular type and interlobular bile ducts with a single-layer cubic epithelium

Figure: 4 - Internal structure of the hepatic lobule

Portal hepatic lobule. It is formed by segments of three adjacent classical hepatic lobules surrounding the triad. It has a triangular shape, in its center lies the triad, and on the periphery (at the corners) there are central veins.

The hepatic acinus is formed by segments of two adjacent classic lobules and has a diamond shape. At the sharp corners of the rhombus, the central veins pass, and the triad is located at the middle level. The acinus, like the portal lobule, does not have a morphologically outlined border, similar to the connective tissue layers that delimit the classic hepatic lobules.

Liver functions:

deposition, glycogen, fat-soluble vitamins (A, D, E, K) are deposited in the liver. The vascular system of the liver is capable of depositing blood in fairly large quantities;

participation in all types of metabolism: protein, lipid (including cholesterol metabolism), carbohydrate, pigment, mineral, etc.

detoxification function;

barrier - protective function;

synthesis of blood proteins: fibrinogen, prothrombin, albumin;

participation in the regulation of blood coagulation by the formation of proteins - fibrinogen and prothrombin;

secretory function - the formation of bile;

homeostatic function, the liver is involved in the regulation of metabolic, antigenic and temperature homeostasis of the body;

Villus structure, parietal digestion

The villus consists of intestinal epithelium, lymphatic sinus, arterial vessel, venous vessel, and blood capillaries.

Parietal digestion is the most efficient and biologically feasible form of digestion. It occurs in the mucus layer between the microvilli of the small intestine and directly on their surface. Enzyme activity increases on the intestinal wall. In addition, the cleavage products pass into the blood without additional movement from the intestinal cavity to the microvilli.

Structural and functional unit of the liver (hepatic lobule). Liver function

The liver is the largest internal organ that performs vital functions in the body and contributes to the functions of many body systems. The liver is involved in the metabolism of all nutrients, in digestion, in the synthesis and reservation of a number of substances necessary for the body, in the breakdown, detoxification and excretion of substances unnecessary or harmful to the body, in hematopoiesis and a number of other functions.

The structural and functional unit of the liver is the liver lobule. In the human liver there are ~ 500,000 hepatic lobules. The lobule has the shape of a prism with a maximum cross-sectional diameter of ~ 1.0 h 2.5 mm. The space between the lobules is filled with a small mass of connective tissue. It contains the interlobular bile ducts, arteries and veins. Usually, the interlobular artery, vein and duct are located side by side, forming the hepatic triad.

The lobules of the liver are built from connecting hepatic plates in the form of doubled radially directed rows of hepatic cells, hepatocytes. In the center of each lobule is the central vein. The inner ends of the hepatic plates are facing the central vein of the lobule, and the outer ends of the plates are facing the periphery of the lobule. Sinusoidal capillaries are also located radially between the hepatic plates, as well as hepatocytes. They carry blood from the periphery of the lobule to its center, to the central vein of the lobule.

Liver - the largest human gland - its mass is about 1.5 kg. It performs a variety of functions and is a vital organ. The metabolic functions of the liver are extremely important for maintaining the vitality of the body, and therefore it is called the biochemical laboratory of the body. In the liver, bile is formed, which is necessary for the absorption of fats and the stimulation of intestinal motility. About 1 liter of bile is released per day.

Liver is an organ that acts as a blood depot. Up to 20% of the total blood mass can be deposited in it. In embryogenesis, the liver performs a hematopoietic function.
Liver development... The liver bud appears at the end of the 3rd week of embryogenesis from the endodermal lining of the ventral midgut wall. The protrusion of this wall grows, forming epithelial cords in the mesenchyme of the mesentery. Later, the cords are divided into cranial and caudal sections, from which the liver and gallbladder with ducts are formed, respectively.

In histogenesis heterochronous divergent differentiation of hepatic epithelial cells (hepatocytes) and bile duct epithelial cells (cholangiocytes) occurs. Starting from the second half of embryogenesis, structural and functional units are formed in the liver - hepatic lobules. Lobule formation is the result of complex interactions between the epithelium and intrahepatic connective tissue with developing sinusoidal blood capillaries.

Liver structure... In the liver, an epithelial parenchyma and a connective tissue stroma are distinguished. The structural and functional units of the liver are hepatic lobules, about 500 thousand in number. The hepatic lobules have the form of hexagonal pyramids with a diameter of up to 1.5 mm and a slightly higher height, in the center of which is the central vein. Due to the peculiarities of hemomicrocirculation, hepatocytes in different parts of the lobule find themselves in different conditions of oxygen supply, which affects their structure.

Therefore, in a lobule the central, peripheral and intermediate zones located between them are distinguished. The peculiarity of the blood supply to the hepatic lobule is that the intralobular artery and vein extending from the arteries and veins around the lobules merge and then the mixed blood moves along the hemocapillaries in the radial direction towards the central vein. Intralobular hemocapillaries run between the hepatic beams (trabeculae). They have a diameter of up to 30 microns and belong to the sinusoidal type of capillaries.

Thus, through intralobular capillaries mixed blood (venous - from the portal vein system and arterial - from the hepatic artery) flows from the periphery to the center of the lobule. Therefore, hepatocytes in the peripheral zone of the lobule find themselves in more favorable conditions for oxygen supply than those in the center of the lobule.

Along the interlobular connective tissue, normally poorly developed, are blood and lymph vessels, as well as excretory bile ducts. As a rule, the interlobular artery, interlobular vein and interlobular excretory duct go together, forming the so-called liver triads. The collecting veins and lymphatic vessels pass at some distance from the triads.

Liver epithelium consists of hepatocytes, which make up 60% of all liver cells. The performance of most of the functions characteristic of the liver is associated with the activity of hepatocytes. At the same time, there is no strict specialization between the liver cells, and therefore the same hepatocytes produce both exocrine secretions (bile) and, by the type of endocrine secretion, numerous substances entering the bloodstream.