20 Liver Stem Cells

Abstract

HEPATIC STEM CELLS The adult mammalian liver contains many different cell types of various embryological origins. Nevertheless, the term liver or hepatic stem cells is used for precursors of the two epithelial liver cell types, the hepatocytes and the bile duct epithelial cells. This terminology also applies to this chapter where only hepatocyte and the bile duct stem cells are discussed. ORGANIZATION AND FUNCTION OF ADULT MAMMALIAN LIVER Anatomy The liver is a large parenchymal organ consisting of several separate lobes and representing about 2% of the body weight in the human and 5% in the mouse (Desmet 1994). It is the only organ with two separate afferent blood supplies. The hepatic artery provides oxygenated blood, and the portal vein brings in venous blood rich in nutrients and hormones from the splanchnic bed (intestines and pancreas). Venous drainage is into the vena cava. The bile secreted by hepatocytes is collected in an arborized collecting system, the biliary tree, which drains into the duodenum. The gall bladder is part of the distal biliary tree and acts to store bile. The hepatic artery, portal vein, and common bile duct enter the liver in the same location, the porta hepatis. The main cell types resident in the liver are hepatocytes, bile duct epithelium, stellate cells (formerly called Ito cells), Kupffer cells, vascular endothelium, fibroblasts, and leukocytes (Desmet 1994). Although hepatocytes are responsible for most organismal liver function and represent about 90% of the weight of the liver, they are large cells and only...