Stem cells are cells that have the potential to develop into some or many different cell types in the body, depending on whether they are multipotent or pluripotent. Serving as a sort of repair system, they can theoretically divide without limit to replenish other cells for as long as the person or animal is still alive. When a stem cell divides, each "daughter" cell has the potential to either remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell.
Stem cells are classified into the following categories:
• Totipotent: Stem cells that can give rise to all cell types that are found in an embryo, fetus, or developed organism, including the embryonic components of the trophoblast and placenta required to support development and birth
• Pluripotent: Stem cells that can become all the cell types that are found in an implanted embryo, fetus, or developed organism, but not embryonic components of the trophoblast and placenta (these are usually called extra-embryonic).
• Multipotent: Stem cells whose progeny are of multiple differentiated cell types, but all within a particular tissue, organ, or physiological system.
• Unipotent: Stem cells that self-renew as well as give rise to a single mature cell type; e.g., spermatogenic stem cells.
Graphic Organizer
http://stemcells.nih.gov/StemCells/Templates/StemCellContentPage.aspx?NRMODE=Published&NRNODEGUID=%7bA604DCCE-2E5F-4395-8954-FCE1C05BECED%7d&NRORIGINALURL=%2finfo%2ffaqs%2easp&NRCACHEHINT=NoModifyGuest#whatare
http://www.stemcellresources.org/celltalk_lesson_2.html
http://isscr.org/Glossary_of_Stem_Cell_Related_Terms.htm#Multipotent
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