What are stem cells?
Stem
cells are cells that have the remarkable potential to
develop into many different cell types in the body during early life and
growth. In addition, in many tissues they serve as a sort of internal repair
system, dividing essentially without limit to replenish other cells as long as
the person or animal is still alive. When a stem cell divides, each new cell
has the potential either to remain a stem cell or become another type of cell
with a more specialized function, such as a muscle cell, a red blood cell, or a
brain cell.
Stem
cells are distinguished from other cell types by two important characteristics.
First, they are unspecialized cells capable of renewing themselves through cell division, sometimes after long
periods of inactivity. Second, under certain physiologic or experimental
conditions, they can be induced to become tissue- or organ-specific cells with
special functions. In some organs, such as the gut and bone marrow, stem cells
regularly divide to repair and replace worn out or damaged tissues. In other
organs, however, such as the pancreas and the heart, stem cells only divide
under special conditions.