Stem cells are precursor, unspecified, undifferentiated group of cells capable of self proliferation, migration and differentiation.Stem Cells are the cells that are able to give rise to more specialized cells, or differentiate into a specific cell type and appear to be one of the body's ablest tools for self-repair.
When a disease or injury strikes, these stem cells respond to specific signals and set about to facilitate healing by differentiating into specialized cells required for the body's repair. That is, provided they exist in sufficient numbers and receive the correct signals when disease or injury occurs. When they do not, the end result is an inadequate or compromised healing response.
There are two important characterstics of stem cells from other cells in the body:-
1. Stem cells can replenish their nature for long period through cell division.
2. Stem cells can differentiate or transform into specialized cells with specific functions after recognizing some chemical signal in the body.
Stem cells can be classified into four broad categories, based on their ability on differentiation:-
1.Totipotent stem cells: are found only in early embryos, each cell can form a complete organism.
2.Pluripotent stem cells: exist in the undifferentiated inner cell mass of the blastocyst and can form all of the over 200 different cell types in the body.
3.Multipotent stem cells: are derived from fetal tissue, cord blood, bone marrow etc. although their ability to differentiate is more limited than pluripotent stem cells.
4.Unipotent stem cells: are found in multipotent cells and adult tissues. They are also able to renew and give rise to only a single mature cell type.