Adult stem cells
Adult stem cells are cells which can be found among differentiated cells in a certain tissue. They can renew themselves and they can differentiate into specific cell types of their original tissue. The basic role of adult stem cells is to repair damaged tissue where they are located. The origin of adult (or somatic) stem cells is unknown.
Somatic stem cells have been discovered in the 1960s. Scientists have found that bone marrow is made out of two types of cells: hematopoietic stem cells and bone marrow stromal cells.
These cells can be found in many places in a human organism. Of course, it is important to mention that there is a very small number of stem cells in each organ or tissue. Tissues and organs which contain stem cells are brain, bone marrow, skeletal muscle, skin, liver.
Adult stem cells, apart from being able to differentiate into cell types of their original tissue, can sometimes differentiate into cell types of other tissues. This is called plasticity.