Stem cells have the ability to change into several different cell types in the body during early life and development. Additionally, in several tissues they serve as a kind of repair system for the human body, dividing limitlessly to replenish other cells so long as the human or animal remains alive. When a stem cell splits, new cells have the potential to remain either a stem cell or become a different kind of cell with a more distinctive role, such as a muscle cell, a red blood cell or a brain cell.
Scientific studies of stem cells allow scientists to discover the cells’ essential properties and what differentiates them from specialized cell types. Scientists have begun to use stem cells in the laboratory to screen new drugs and to develop systems to study normal growth and observe the causes of birth defects.