An embryo develops from a fertilised egg. Cells at the early stages in the development of the embryo are stem cells.
If cells are removed from the embryo - called embryonic stem cells - they will differentiate into any cell type.
Some stem cells remain in the bodies of adults - adult stem cells. Adult stem cells are found in limited numbers at certain locations in the body.
Adult stem cells can be found in several regions of the body, including the: