Adult stem cells are undifferentiated cells, found throughout the body after development, that multiply by cell division to replenish dying cells and regenerate damaged tissues. Also known as somatic stem cells (from Greek Σωματικóς, meaning ''of the body''), they can be found in juvenile as well as adult animals and human bodies.
Scientific interest in adult stem cells is centered on their ability to divide or ''self-renew'' indefinitely, and generate all the cell types of the organ from which they originate, potentially regenerating the entire organ from a few cells. Unlike embryonic stem cells, the use of human adult stem cells in research and therapy is not considered to be controversial, as they are derived from adult tissue samples rather than human 5 day old embryos generated by IVF (in vitro fertility) clinics designated for scientific research. They have mainly been studied in humans and model organisms such as mice and rats.
A stem cell possesses two properties:
* ''Self-renewal'', which is the ability to go through numerous cycles of cell division while still maintaining its undifferentiated state.
* ''multipotency'' or ''multidifferentiative potential'', which is the ability to generate progeny of several distinct cell types, (for example glial cells and neurons) as opposed to unipotency, which is the term for cells that are restricted to producing a single-cell type. However, some researchers do not consider multipotency to be essential, and believe that unipotent self-renewing stem cells can exist.〔
ISSN:(1549-3199 ). LCCN:(2004212209 ). OCLC:.〕 These properties can be illustrated with relative ease ''in vitro'', using methods such as clonogenic assays, where the progeny of a single cell is characterized. However, it is known that ''in vitro'' cell culture conditions can alter the behavior of cells, proving that a particular subpopulation of cells possesses stem cell properties ''in vivo'' is challenging, and so considerable debate exists as to whether some proposed stem cell populations in the adult are indeed stem cells.
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