Stem cells are cells of the body (somatic cells) which can divide and become differentiated.p425
When an organism grows, stem cells specialize, and take specific functions. For instance, mature tissues like skin, muscle, blood, bone, liver, nerves, all have different types of cell. Because stem cells are not yet differentiated, they can change to become some kind of specialized cells. Organisms also use stem cells to replace damaged cells during lifetime.
Stem cells are found in most, if not all, plants and animals. They divide and differentiate into a range of cell types. Research in the stem cell field grew out of findings in the 1960s.
The two broad types of mammalian stem cells are: embryonic stem cells, and adult stem cells, which are found in adult tissues. In a developing embryo, stem cells can differentiate into all of the specialised embryonic tissues. In adult organisms, stem cells act as a repair system for the body, replenishing specialized cells, but also maintain the normal turnover of blood, skin, and intestinal tissues.
Stem cells can be grown in cell culture. In culture, they can be transformed into specialised cells, such as those of muscles or nerves. Highly plastic adult stem cells from a variety of sources, (umbilical cord, blood, bone marrow), are now routinely used in medical therapies. Researchers expect that stem cells will be used in many future therapies.
Embryonic stem cells
[[File:|250px|thumb|left|Human embryonic stem cell colony.]]
Embryonic stem cells (ES cells) are stem cells taken from the inner cell mass of the early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4-5 days after fertilization. At that time, they are made up of between 50 and 150 cells.
The stem cells' state, and what the daughter cells turn into, is influenced by signals from other cells in the embryo.
- ↑ King R.C. Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics, 7th ed. Oxford.
- ↑ Becker AJ, McCulloch EA, Till JE (1963). [Expression error: Unexpected < operator "Cytological demonstration of the clonal nature of spleen colonies derived from transplanted mouse marrow cells"]. Nature 197: 452–4. doi:10.1038/197452a0. PMID 13970094.
- ↑ Siminovitch L, McCulloch EA, Till JE (1963). [Expression error: Unexpected < operator "The distribution of colony-forming cells among spleen colonies"]. Journal of Cellular and Comparative Physiology 62: 327–36. doi:10.1002/jcp.1030620313. PMID 14086156.
- ↑ Tuch BE (2006). [Expression error: Unexpected < operator "Stem cells—a clinical update"]. Australian Family Physician 35 (9): 719–21. PMID 16969445.