Stem cells

Stem cells are special cells able to renew themselves and replace dead cells.

There are four different types of stem cells:
 * Totipotent
 * Can create all cell types
 * Pluripotent
 * Can create many cell types, but not all
 * Multipotent
 * Can only develop into a few cell types
 * Unipotent
 * Can only develop into one cell type - muscle stem cells