[Hepatic stem cells]

The presence of hepatic stem cells had been postulated for a long time, until several papers on the pathogenesis of hepatic diseases have recently revealed their presence. Hepatocytes belonging to liver parenchyma show morphological, biochemical and functional differences, as well as different proliferation capacity and pattern of gene expression. Hepatocytes and ductal biliary cells have a common embryologic origin: the endodermal multipotential cells, that migrate and differentiate in response to signals received from the portal mesenchyma. Hepatic regeneration is normally produced through activation of mature cells. However, when the hepatic damage is very extensive, the activation of facultative stem cells localized in the Hering canal, produces the oval cells, with bipotential capacity. Specific antigenic markers for these cells and others shared with fetal cells have been developed, Cells with characteristics similar to those oval cells described in rodents were found in the human liver. A new insight on this subject has opened up with the obtention of hepatic cells from bone marrow stem cells. In this sense, several experiments were carried out using animal and human models. These and others performed with different cellular types obtained from bone marrow, indicate that hematopoietic stem cells could be itinerant cells subject to tissue specific differentiation. The activation of stem cells in order to generate new hepatocytes and ductal biliary cells, is relevant in terms of the study of the pathophysiology of several diseases, such as cancer or the regenerative activity of hepatic parenchyma after massive destruction.