Stem Cells

Stem cells appear in many organs of the body. They are quite different to the other “differentiated” cells – they can make copies of themselves (and the copies can make more copies, a process called "replication"), and they can also make the “differentiated” cells of the organ in which they are found. (Strictly speaking, they generate ‘progenitor cells’, which produce differentiated cells). So, for example, a stem cell in the bone marrow generates both more stem cells and also bone marrow progenitors.

Because a stem cell can make copies of itself, a single stem cell can be used, in a laboratory, to grow many more stem cells.

When a baby is born, it has developed from a single fertilized egg cell. This splits into two, then four, then eight (and so on) other cells, until there is a small clump of cells (the morula). These cells will eventually reproduce themselves and become the cells for every part of the body – they are stem cells. As the embryo develops, cells become more “differentiated” and organs appear. As a child develops, the proportion of stem cells, compared to the total number of cells, decreases. About one in ten thousand cells of an adult are stem cells.