The hepatic portal vein is a vessel that moves blood from the spleen and gastrointestinal tract to the liver's capillary beds. It is about three to four inches and length and is usually formed by the convergence of the superior mesenteric and splenic veins behind the upper edge of the head of pancreas. In some individuals, the inferior mesenteric vein may enter this junction instead. The portal vein supplies approximately 75 percent of hepatic blood flow. The portal vein is not a true vein in that it does not drain into the heart. Instead, its functions are to supply metabolic substrates to the liver and to maintain that ingested substances are first processed by the liver before entering normal circulation. Abnormally high blood pressure in the portal vein is known as portal hypertension. The condition may cause the growth of collateral blood vessels that bypass the liver, which can result in the circulation of unprocessed substances throughout the body. Portal hypertension is a major complication of liver cirrhosis.
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In Depth: Portal vein