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Author(s): MarkAbraham, JeromeCrowley

  1. Liver structure
    1. The anatomic unit of the liver is lobule. The lobule is composed of hexagonal plates of hepatocytes and portal triads (terminal portal vein, hepatic artery, and bile duct branch) surrounding a central hepatic vein.
    2. Hepatocytes are classified by their position in relation to their portal triad. Those closest to the triad are labeled Zone 1 cells (periportal). These cells receive the most oxygen and nutrients and are responsible for most nitrogen metabolism, oxidation, and gluconeogenesis. Zone 2 is a transitional area. Zone 3 hepatocytes (pericentral) are the farthest from the triad and are at the greatest risk for ischemic injury.
  2. Hepatic blood supply. The liver comprises only 2% of the total body mass, but it receives 20% to 25% of the cardiac output.
    1. The hepatic artery supplies 25% of the total liver blood flow and 50% of the liver’s oxygen requirement.
    2. The portal vein drains the stomach, spleen, pancreas, and intestine. It supplies 75% of the hepatic blood flow and 50% of hepatic oxygen.
    3. Total hepatic blood flow depends greatly on venous return from the preportal organs. Flow in the hepatic artery is regulated by sympathetic tone and local adenosine concentration and is inversely related to portal vein flow (PVF). A reduction in PVF will lead to an increased adenosine concentration in the liver, which causes local arteriole dilation and an increase in hepatic artery flow. Total hepatic blood flow may be reduced in diseases causing increased hepatic vascular resistance (eg, cirrhosis, infiltrative disease as in metastatic liver disease, and Budd-Chiari syndrome).