Liver Organization

Portal triads convey blood into the liver and bile out of the liver. Hepatic venules surround portal triads and drain blood from the liver. In between the portal triads and hepatic venules lie hepatocytes that secrete bile and process nutrients, toxins and other material in the blood from the portal triad. The red arrows show the direction that blood flows from the portal triad to hepatic venule, whereas the yellow arrows show the flow of bile from hepatocytes to portal triad. Hepatocytes are functionally divided into three zones depending on their proximity to portal triads and arterial blood supply. Zone 1 is exposed to fresh arterial blood with a high concentration of oxygen, but as the blood percolates into zone 2 and zone 3, the concentration of oxygen falls. Consequently, the hepatocytes in the zones have different metabolic activities.