The facultative stem cell: A new star in liver pathology.

Although the unlimited capacity of hepatocytes to divide has been recently proven, more and more evidences support the existence of a primitive stem cell compartment in the liver. These cells probably do not participate in the usual maintenance of the liver mass, but they are activated in case of extensive hepatocyte injury. In vivo the oval cells show deep similarly to the primitive cells of the embryonic liver and seem to be the amplification compartment of the hepatic stem cells. A primitive epithelial cell population can be isolated from the normal liver and maintained in vitro. Studies of these two experimental systems provide most of the data about liver stem cells, which may become important for the clinical practice if we understand how their growth is regulated.