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 cells. 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.
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 tissue culture. In culture, they can be transformed into specialised cells, such as those of muscles or nerves. Highly plastic adult stem cells can be taken from a variety of sources, including umbilical cord blood and bone marrow. They are now used in medical therapies, and researchers expect that stem cells will be used in many future therapies.
Embryonic stem cells[change | change source]
Embryonic stem cells (ES cells) are stem cells taken from the inner cell mass of the early stage embryo called 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.
Adult stem cells[change | change source]
Adult stem cells exist throughout body after embryonic development has completed. They are found inside different types of tissue and remain in a non-dividing state until disease or tissue injury. They have changed permanently into specialised cells and have lost the ability to divide and specialise further.
Plant stem cells[change | change source]
Plant stem cells are unspecialised, and can develop into any type of plant cell. They become specialised into cells of roots, leaves or flowers. The stem cells are found in meristem, at root and stem apices. They make it possible for growth to continue.
Cloning plants[change | change source]
These are plants which have been grown from cuttings (therefore the same plant). They are dipped in hormone rooting powder to develop bigger root systems. They turn into tissues (eg. xylem and phloem) and organs (eg. roots, leaves and flowers), therefore becoming a completely new plant.
Cloning plants is a cheap way of producing a new plant.
Stem cells in medicine[change | change source]
Some cancers may be treated by stem cells. Leukemia, a cancer of white blood cells (WBC) is an example.
There are two stages to this process:
- Chemotherapy and radiotherapy to kill cancerous white blood cells and stop the production of more. However, this may leave the patient with a severely compromised immune system with a risk of infection.
- A transplant of bone marrow containing healthy stem cells (to produce normal WBC).
Other websites[change | change source]
References[change | change source]
- King R.C. Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics, 7th ed. Oxford. p425.
- Becker AJ, McCulloch EA, Till JE (1963). "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). "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). "Stem cells—a clinical update". Australian Family Physician 35 (9): 719–21. PMID 16969445.