The liver is not only the largest organ, other than skin, in the body (approximately 1.5 kilograms), but might also be said to have the most diverse roles of any organ in the body. Over 500 different functions are ascribed to the liver. Of its many critical roles, some are related to digestion and some are unrelated. For instance, the liver serves as an exocrine gland, secreting bile into the small intestine to help solubilize fats for digestion and absorption, but the liver also serves as an important storage organ and endocrine gland, secreting many important substances into the blood.

The liver blood supply is unusual in the sense that it derives from two sources, the hepatic artery (20%) and the portal vein (80%). The portal vein carries oxygen-poor, nutrient-rich blood from the intestine, pancreas, and spleen. It branches to send portal venules to the portal triads, which branch again sending smaller venules around the periphery of the lobule. From these arise smaller venules that empty into the sinusoids. Oxygen is supplied to liver cells by the hepatic artery, which carries oxygen-rich blood from the aorta. It branches to form the interlobular arteries, which branch to empty directly into the sinusoids, thus mixing oxygen-rich arterial and nutrient-rich portal venous blood around the hepatocytes. The sinusoids conduct the blood centrally, converging into the central vein. Central veins leave the lobules at their base as the sublobular veins, which converge to form the hepatic veins and empty into the inferior vena cava.