<P> The portal vein or hepatic portal vein is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver . This blood contains nutrients and toxins extracted from digested contents . Approximately 75% of total liver blood flow is through the portal vein, with the remainder coming from the hepatic artery proper . The blood leaves the liver to the heart in the hepatic veins . </P> <P> The portal vein is not a true vein, because it conducts blood to capillary beds in the liver and not directly to the heart . It is a major component of the hepatic portal system, one of only two portal venous systems in the body--with the hypophyseal portal system being the other . </P> <P> The portal vein is usually formed by the confluence of the superior mesenteric and splenic veins and also receives blood from the inferior mesenteric, gastric, and cystic veins . </P> <P> Conditions involving the portal vein cause considerable illness and death . An important example of such a condition is elevated blood pressure in the portal vein . This condition, called portal hypertension, is a major complication of cirrhosis . </P>

Which three veins empty into the porta vein
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