Abstract

The liver is unique to the adult body in its regenerative capacity following injury, with the ability to regrow large masses of tissue following surgical resection, an ability that declines only at late ages. More surprisingly, this appears to occur with only minimal contribution from resident stem cell populations. Rather, differentiated parenchymal cell types including hepatocytes and cholangiocytes appear capable of massive proliferation to replace lost tissue. The role of precursor cell types in the liver is confusing, due to the plasticity of cell types, with trans-differentiation between cell types and between mature and progenitor cells, the potential existence of a sub-population of hepatocytes dedicated to proliferation, and the highly levels of polyploidy in hepatocytes that may act as an unusual form of reductive mitosis through the "ploidy conveyor belt." In this chapter, we discuss the composition of the liver in terms of its cell types, the existence of progenitors for each of these, mechanisms for declining regenerative capacity with age, and the impacts of this on human physiology.