Hepatic Portal Vein
The hepatic portal vein is one of the most important vein that receives blood from the body and transports it into the liver for filtration and processing. This vein is part of the hepatic portal system that receives all of the blood draining from the abdominal digestive tract, as well as from the pancreas, gallbladder, and spleen. ‘Hepatic’ means of or relating to the liver, therefore the hepatic portal vein is a blood vessel that sends nutrient-rich blood from the gastrointestinal tract and spleen to the liver.
Generally, the hepatic portal vein is about 8 centimeters (3 inches) long in adults, and is located in the upper right quadrant of the abdomen, which originates behind the neck of the pancreas and is part of the hepatic portal system.
While there may be some variations between individuals, the hepatic portal vein is usually formed by the convergence of the superior mesenteric vein and the splenic vein, referred to as the splenic-mesenteric confluence.
In some individuals, the hepatic portal vein also directly joins with the inferior mesenteric vein. Even less common, but also possible anastomoses are the cystic and gastric veins.
The liver receives blood from two sources: the hepatic portal vein (70%), and the hepatic arteries (30%). The hepatic portal vein receives blood specifically from the stomach, intestines, pancreas, and spleen, and carries it into the liver through the porta hepatis. The porta hepatis serves as the point of entry for the hepatic portal vein and the proper hepatic artery, and is the point of exit for the bile passages.
However, before reaching the liver, the portal vein bisects into the left and right, with each side further dividing from venous branches into portal venules. These portal venule branches run alongside hepatic arterioles in the spaces between the liver lobules, and these two vessels, along with a common bile duct, form the hepatic portal triad. These vessels all empty eventually into the hepatic sinusoids to supply blood to the liver, which also means that there is an unusual mixing of venous and arterial blood in the sinusoids.
Following processing of the blood by the hepatocytes (chief functional cells of the liver), the blood collects in the central vein at the core of the lobule. Blood from these central veins will ultimately converge in the right and left hepatic veins, which exit the superior surface of the liver and empty into the inferior vena cava to be distributed to the rest of the body.
The hepatic portal system is so named since it connects capillaries of the intestines and other digestive organs to modified capillaries (hepatic sinusoids) of the liver. As intestinal blood is nutrient-rich for a few hours post-prandial (after a meal), the hepatic portal system will be able to claim available nutrients before blood is distributed to the rest of the body.
Additionally, the hepatic portal system plays a key role in cleansing the blood of the bacteria and toxins that are picked up by the blood while it is being perfused through the intestines.
Other than the previously mentioned hepatic and related veins, the principal associated intestinal veins are the inferior mesenteric vein, superior mesenteric vein, and the splenic vein (which converges with the pancreatic veins before it meets the inferior mesenteric vein, and ultimately meets the superior mesenteric vein). The left and right gastric veins, which form an arc along the lesser curvature of the stomach, also empty into the hepatic portal vein. Broadly, the hepatocytes that process the blood play a large role in protein synthesis, carbohydrate metabolism, lipid metabolism, and detoxification.
Portal hypertension is defined as an increase in blood pressure in the portal vein, and is a major complication of liver disease (most commonly cirrhosis, often from excessive alcohol consumption). Notable characteristics of chronic liver disease can include:
- esophageal varices
- spider nevi
- caput medusae
- palmar erythema