The portal vein is a major vein in the human body draining blood from the digestive system and its associated glands. It is formed by the union of the splenic and superior mesenteric veins. It divides into a right and left branches, before entering the liver.

Note that the portal vein drains blood into the liver not from the liver. The blood entering the liver from the portal vein will then leave to the inferior vena cava through the hepatic veins .

A second portal vein system connects hypothalamus and pituitary thus transferring releasing hormones with high concentration to the anterior pituitary lobe.

Tributaries

The portal vein drains:

• The posterior superior pancreaticoduodenal vein
• The right gastric vein
• The left gastric vein

Physiology

Almost all of the blood coming from the digestive system drains into a special venous circulation called the portal circulation . This is because it contains all the nutrients and toxins that have been absorbed along the digestive tract from ingested food. Before these absorbed substances can go into the systemic circulation (the main blood circulation in the body), it must be filtered first to remove or "detoxify" toxins first. This filtering and detoxification is one of the functions of the liver.

Role in disease

Increased blood pressure in the portal vein, portal hypertension, occurs in liver disease (mainly cirrhosis), and may lead to various complications (ascites, esophageal varices, spontaneous bacterial peritonitis). A disruption of the hypothalamo-pituitary portal veins is referred to as Pickardt syndrome (suprasellar failure).