What Are Stem Cells

"A stem cell may be defined as an undifferentiated cell capable of self-renewal and of giving rise to one or more differentiated cell types."

Stem cells 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 is alive.

The human body is made up of about 200 different kinds of specialized cells such as muscle cells, nerve cells, fat cells and skin cells. All specialized cells originate from stem cells. A stem cell is a cell that is not yet specialized. The process of specialization is called differentiation and once the differentiation pathway of a stem cell has been decided, it can no longer become another type of cell.

The defining characteristic of human stem cells is their ability to self-renew while maintaining the potential to develop into other types of cells. Although stem cells from different sources all share these general characteristics, there are also significant differences among them. Different types of stem cells have different levels of potential. A stem cell that can become every type of cell in the body is called pluripotent and a stem cell that can become only some types of cells is called multipotent.