Stem cells have the potential to become many different cell types in our bodies. Serving as basically repair system for the body, they can theoretically divide an unlimited number of times unless the organism dies. When the stem cell divides, each new daughter cell has the potential to either remain a stem cell or become a cell with a more specialized function i.e. Muscle, Red Blood Cell, Brain Cell, etc.
There are two basic types of Stem Cells, Embryonic and Adult, the major difference is that the embryonic stem cells can become literally any type of cell in our bodies, while Adult stem cells can only become cells from their tissue of origin. Although this may or may not be entirely true as new evidence suggests that plasticity may exist within these Stem Cells which greatly increase the number of cell types possible to an Adult Stem Cell. Anther major difference is that large numbers of Embryonic stem cells can be grown in cultures whereas scientist are yet to figure out how to do the same with the adult stem cells. While it doesn't sound as if the Adult stem cells would be as useful as the embryonic ones the Adult ones hold one major advantage over the embryonic ones. When we do figure out how to differentiate the undifferentiated Stem Cells in to the needed cells we can easily reintroduce these cells back into the body without them suffering from immune rejection.
This Research into Stem Cells is revolutionary and in future will lead to new exciting forms of Medicine and the possibility of cell-based therapies to treat disease, which is often referred to as Regenerative or Reparative medicine.
Unfortunately there are still many obstacles remaining that we have to overcome before we can truly unlock the potential of these Stem Cells. Key among these is determining how Undifferentiated Stem Cells become differentiated.
More Info. http://stemcells.nih.gov/info/basics/
