Stem cells are cells that are able to produce a copy of themselves by dividing. However, divisiondoes not create two new stem cells, it is an asymmetric cell division that creates two different cells. One of the newly created cells is a duplicate of the mother cell and has the same characteristics, i.e. a new stem cell is created. The other cell, which was created by asymmetric cell division, develops into a specialized cell type, i.e. it differentiates. The stem cells are then able to mature by differentiation into further cell types and represent an essential basis for the development of complex tissues and organs, such as the heart and kidneys.
Through the mechanism of asymmetric cell division, it is possible both to maintain the pool of stem cells and to form new cells for differentiation.
When we talk about stem cells, we have to distinguish between different stem cell types. They differ in their potential to form different cell types by division.