Progenitor cells are similar to stem cells in that they have a capacity for self-renewal and differentiation. While standard distinctions between stem cells and progenitors are still evolving, it is understood that such abilities in the progenitor cells are only very limited. Progenitors are unipotent, and in some cases oligopotent, differentiating into only one or a few cell types. Their main function is believed to be in tissue repair, becoming activated to replenish damaged or dead cells upon injury. Like stem cells, they are valued for their potential applications in regenerative medicine. Some of the more well studied progenitors include satellite muscle cells, neural progenitor cells, endothelial progenitor cells, pancreatic progenitors and hematopoietic progenitor cells.