The liver has a dual blood supply. The portal vein (which is rich in nutrients and relatively high in O₂) provides two thirds of blood flow to the liver. The hepatic artery (which is O₂-rich) supplies the rest. The hepatic veins drain the liver into the inferior vena cava. When portal vein blood flow increases, hepatic artery flow decreases and vice versa (the hepatic arterial buffer response). This dual, reciprocally compensatory blood supply provides some protection from hepatic ischemia in healthy people.

Despite its dual blood supply, the liver, a metabolically active organ, can be injured by

• Ischemia: Ischemia results from reduced blood flow, reduced O₂ delivery, increased metabolic activity, or all 3.
• Insufficient venous drainage: The cause may be focal or diffuse obstruction. Manifestations of focal venous obstruction depend on the location. Diffuse venous congestion causes congestive hepatopathy. Reduced venous outflow from the liver (originating in the hepatic veins or within the liver itself, usually from cirrhosis) results in portal hypertension.
• Specific vascular lesions: The hepatic artery, hepatic vein, or portal vein may be involved. In peliosis hepatis, the vascular lesion occurs in the sinusoids (microvascular anastomoses between the portal and hepatic veins).

Last full review/revision December 2007 by Eldon A. Shaffer, MD