portal system n a system of veins that begins and ends in capillaries see HEPATIC PORTAL SYSTEM, PITUITARY PORTAL SYSTEM
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a vein or group of veins that terminates at both ends in a capillary bed. The best known is the hepatic portal system, which consists of the portal vein and its tributaries. Blood is drained from the spleen, stomach, pancreas, and small and large intestines into veins that merge to form the portal vein leading to the liver. Here the portal vein branches, ending in many small capillaries called sinusoid. These permit the passage into the liver cells of nutrients absorbed by blood from the intestines.
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an arrangement of vessels whereby blood collected from one set of capillaries passes through a large vessel or vessels and then through a second set of capillaries before it returns to the systemic circulation, such as in the hepatic portal circulation and the hypothalamo-hypophysial portal system.Medical dictionary. 2011.