Definition
A portal vein is a blood vessel that carries blood from one capillary bed to another, without first going through the heart. Unlike regular veins, it doesn't directly return blood to the heart. Its main job is to deliver blood to a specific organ for processing. The most important example is the hepatic portal vein, which transports blood from the digestive organs to the liver. This ensures the liver can process nutrients and detoxify the blood before it enters general circulation.