portal vein, a vein from the small intestine that ramifies in the liver and ends in capillary-like sinusoids that convey the blood to the inferior vena cava through the hepatic veins. The portal vein passes behind the duodenum and ascends through the lesser omentum to the porta hepatis, where it divides into the right and left branches. The vein is surrounded by the hepatic plexus of nerves and is accompanied by numerous lymphatic vessels, some lymph nodes, and corresponding branches of the hepatic artery. The right branch of the portal vein enters the right lobe of the liver, and the left branch enters the left lobe.
