What Are Stem Cells?Stem cells are unique cells of the body in that they are unspecialized and have the ability to develop into several different types of cells. They are different from specialized cells, such as heart or blood cells, in that they can replicate many times, for long periods of time. This ability is what is known as proliferation. Unlike other cells, stem cells also have the ability to differentiate or develop into specialized cells for specific organs or develop into tissues. In some tissues, such as muscle or brain tissue, stem cells can even regenerate to aid in the replacement of damaged cells.
Where Are Stem Cells Found?Stem cells come from several sources in the body. The names of the cells below indicate the sources from which they are derived.
- Embryonic Stem Cells
These stem cells come from embryos in the early stages of development. They have the ability to differentiate into any type of cell in the initial stages of development and become slightly more specialized as they mature.
- Fetal Stem Cells
These stem cells come from a fetus. At about nine weeks, a maturing embryo enters into the fetal stage of development. Fetal stem cells are found in fetal tissues, blood and bone marrow. They have the potential to develop into almost any type of cell.
- Umbilical Cord Blood Stem Cells
These stem cells are derived from umbilical cord blood. Umbilical cord stem cells are similar to those found in mature or adult stem cells. They are specialized cells that develop into specific types of cells.
- Placental Stem Cells
These stem cells are contained within the placenta. Like cord blood stem cells, these cells are specialized cells that develop into specific types of cells. Placentas however, contain several times more stem cells than do umbilical cords.
- Adult Stem Cells
These stem cells are present in mature body tissues in infants, children and adults. They may also be found in fetal and umbilical cord blood cells. Adult stem cells are specific to a particular tissue or organ and produce the cells within that particular tissue or organ. These stem cells help to maintain and repair organs and tissues throughout a person's life.
Stem Cell Information : National Institutes of Health
Image: Nissim Benvenisty / Russo E (2005) Follow the Money—The Politics of Embryonic Stem Cell Research. PLoS Biol 3(7): e234. doi:10.1371/journal.pbio.0030234