Portal circulation refers to the circulation of blood from the small intestine to the liver, via the portal vein. Blood flow to the liver is unique in that it receives both oxygenated and deoxygenated blood. As a result, portal blood has lower pO2 and perfusion pressure than the other organs of the body. Blood passes from branches of the portal vein through cavities between "plates" of hepatocytes called sinusoids. Blood also flows from branches of the hepatic artery and mixes into the sinusoids to supply the hepatocytes with oxygen. This mixture percolates through the sinusoids and collects in a central vein which drains into the hepatic vein. The hepatic vein subsequently drains into the inferior vena cava.