System of portal vein

The portal vein (liver) (v. Portae hepatis) occupies a special place among the veins that collect blood from the internal organs. It is not only the largest visceral vein (its length is 5-6 cm, diameter 11-18 mm), but also bringing the venous link of the so-called portal system of the liver. The portal vein of the liver is located in the thickness of the hepatic-duodenal ligament behind the hepatic artery and common bile duct along with nerves, lymph nodes and vessels. It is formed from the veins of the unpaired organs of the abdominal cavity: the stomach, the small and large intestine, the spleen, the pancreas. From these organs, venous blood passes through the portal vein into the liver, and from it through the hepatic veins into the inferior vena cava. The main inflows of the portal vein are the superior mesenteric and splenic veins, as well as the inferior mesenteric vein that merge with one another behind the head of the pancreas. Entering the gates of the liver, the portal vein is divided into a larger right branch (r. Dexter) and a left branch (r. Sinister). Each of the branches of the portal vein, in turn, decomposes first into segmental branches, and then into branches of ever smaller diameter that turn into interlobular veins. Inside the lobes, these veins give wide capillaries - the so-called sinusoid vessels that flow into the central vein. Outgoing from each lobule poddolkovye veins, merging, form three or four hepatic veins. Thus, the blood flowing into the lower vena cava on the hepatic veins passes through two capillary nets on its way. One capillary network is located in the walls of the digestive tract, where the inflow of the portal vein originates. Another capillary network is formed in the liver parenchyma from the capillaries of its lobules.

Before entry into the gates of the liver (in the thickness of the hepatic-duodenum ligament), the gallbladder vein (v. Cystica) from the gall bladder, the right and left gastric veins (v. Gastricae dextra et sinistra) and the vas deferens (v. Prepylorica), enter the portal vein, delivering blood from the corresponding parts of the stomach. The left gastric vein anastomoses with the esophagus veins - the influx of an unpaired vein from the system of the superior vena cava. In the thickness of the circular ligament of the liver, the peri-ocular veins (v. Paraumbilicales) follow the liver. They begin in the anterior abdominal wall, in the navel area, where they are anastomosed with the upper epigastric veins - inflows of the internal thoracic veins (from the system of the superior vena cava) and with superficial and lower epigastric veins - inflows of the femoral and external iliac veins from the inferior vena cava system.

Inflows of the portal vein

1. The superior mesenteric vein (v. Mesentenca superior) goes in the root of the mesentery of the small intestine to the right of the same artery. Its inflows are the veins of the jejunales and ileales, pancreatic veins ( v. Pancreaticael, pancreatic-duodenal veins (vv.rascreaticoduodenales), ilio-vascular vein (v. Ileocolica), right gastro-omental vein (v . Gastroomenialis dextra), right and middle colonic veins (vv. Colicae media et dextra) , Vienna appendix (v. Appendicuiaris). The superior mesenteric vein listed veins bring blood from the walls of the jejunum and ileum and appendix, ascending colon and transverse colon, from the stomach, duodenum oh intestine and pancreas, a large omentum.
2. Splenic vein (v. Splenica) is located along the upper edge of the pancreas below the splenic artery. This vein passes from left to right, crossing the front of the aorta. Behind the head of the pancreas, it merges with the superior mesenteric vein. Inflows of the splenic vein are pancreatic veins (v. Pancieaticae), short gastric veins (v. Gastricae breves) and left gastro-omental vein (v. Gastroomentalis sinistra). The latter anastomoses according to the large curvature of the stomach with the right vein of the same name. The splenic vein collects blood from the spleen, part of the stomach, pancreas and large omentum.
3. The inferior mesenteric vein (v. Mesenterica inferior) is formed by the fusion of the superior rectal vein (v. Rectalis superior), the left colonic vein (v. Colica sinistra) and sigmoid-intestinal veins (vv. Sigmoideae). Located next to the left colonic artery, the inferior mesenteric vein goes up, passes behind the pancreas and flows into the splenic vein (sometimes into the superior mesenteric vein). The inferior mesenteric vein collects blood from the walls of the upper part of the rectum, the sigmoid colon and the descending colon.

In men, the blood flow through the portal vein is about 1000-1200 ml / min.

Oxygen content in portal blood

The maintenance of oxygen in arterial and portal blood on an empty stomach differs only on 0,4-3,3 об.% (On the average, 1,9% vol.); Through the portal vein, 40 ml of oxygen enters the liver every minute, which is 72% of the total oxygen entering the liver.

After eating, the absorption of oxygen by the intestine increases and the difference between arterial and portal blood increases with oxygen content.

Blood flow in the portal vein

The distribution of portal blood flow in the liver is not constant: blood flow to the left or right side of the liver can predominate. A person has a possibility of blood flow from the system of one shared branch to the system of another. The portal blood flow, apparently, is more laminar than turbulent.

The pressure in the portal vein in humans is normally about 7 mm Hg.

[1], [2], [3], [4], [5], [6]

Collateral circulation

If there is an outflow in the portal vein, regardless of whether it is caused by intra- or extrahepatic obstruction, the portal blood flows into the central veins through the venous collaterals, which at the same time expand considerably.

[7], [8], [9], [10], [11],

Intrahepatic obstruction (cirrhosis)

Normally, all portal blood can flow out through the hepatic veins; with cirrhosis of the liver only 13%. The rest of the blood passes through the collaterals, which can be combined into 4 main groups.

• Group I : collaterals passing in the area of transition of protective epithelium into absorbent
  • A. In the cardiac part of the stomach, there are anastomoses between the left, posterior and short veins of the stomach, which are related to the portal vein system, and intercostal, diaphragm-esophageal and semi-unpaired veins that belong to the inferior vena cava system. Redistribution of flowing blood into these veins leads to varicose veins of the submucosal layer of the lower esophagus and stomach bottom.
  • B. In the anal area there are anastomoses between the upper hemorrhoidal vein related to the portal vein system and the middle and lower hemorrhoid veins related to the inferior vena cava system. Redistribution of venous blood in these veins leads to varicose veins of the rectum.
• II group: veins passing in the crescent ligament and connected with the perianopic veins, which are a vestigial of the umbilical cord blood circulation system.
• III group: collaterals passing in the ligaments or folds of the peritoneum that form when it passes from the abdominal cavity to the abdominal wall or retroperitoneal tissue. These collaterals pass from the liver to the diaphragm, in the spleen-kidney ligament and in the omentum. These include the lumbar veins, veins that developed in the scars that formed after previous operations, as well as collaterals formed around the entero or colostomy.
• IV group: veins that redistribute portal venous blood into the left renal vein. Blood flow through these collaterals is carried out either directly from the spleen vein into the renal, and through the diaphragmatic, pancreatic, gastric veins or vein of the left adrenal gland.

As a result, the blood from the gastroesophageal and other collaterals through the unpaired or semi-unpaired vein enters the upper vena cava. A small amount of blood enters the inferior vena cava, it can drain blood from the right lobar branch of the portal vein after forming an intrahepatic shunt. The development of collaterals to pulmonary veins is described.

Extrahepatic obstruction

When extrahepatic obstruction of the portal vein, additional collaterals are formed, along which the blood bypasses the obstruction site in order to get into the liver. They flow into the portal vein in the portal of the liver distal to the site of obstruction. These collaterals include the veins of the liver gates; The veins accompanying the portal vein and the hepatic arteries; veins passing in ligaments supporting the liver; diaphragmatic and glandal veins. Collaterals associated with lumbar veins can reach very large sizes.

[12], [13], [14], [15], [16], [17], [18], [19],