ABSTRACT
Hepatic lobules are, however, structural units that do not tell us much about the secretory function of the liver. Blood flows from the portal triad (supplied by branches of the hepatic artery and the portal vein), past columns of hepatocytes, before draining into the central veins. Liver secretions such as bile, however, are produced by hepatocytes and flow in the opposite direction to the blood, into biliary ducts. Thus one can consider the functional unit of the liver in a secretory sense to consist of all of the cells contained within a prism with a biliary duct at its center (Fig. 1c). This is known as the portal lobule or hepatic acinus, conceptually similar to the acinus of other exocrine glands such as salivary glands (see Topic J2). Within a hepatic acinus, blood flows in one direction and bile flows in
Fig. 1. Liver structure. (a) The structural unit of the liver is the liver lobule; (b) blood supply to the liver and biliary drainage takes place through vessels in the region where three liver lobules abut one another, in the portal triad; (c) the secretory unit of the liver is a hepatic acinus, drained by the biliary duct within the portal triad.
