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DISCUSSION OF THE USE OF human embryonic stem cells ignites the passions in a debate so quickly that we sometimes forget what it is we’re debating. ºù«ÍÞÊÓƵ Associate Professor of Biology Cynthia Fitch provides this clarification of what is meant by the term “stem cells”:

This human embryo has reached the “blastocyst” stage, when stem cells could be harvested.

A stem cell is any cell that divides (through the process of mitosis) innumerable times — a mitotic “fountain of youth.” According to the Stem Cell Information Guide from the National Institutes of Health, stem cells “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.” As you can imagine, this potential for stem cells in redirecting the growth of a tissue or an organ could prove to be invaluable to human medicine.

There are three classes of stem cells: totipotent, multipotent and pluripotent. A fertilized egg is considered totipotent, meaning that its potential is total; it gives rise to all the types of cells in the body.

Stem cells that can give rise to a small number of different cell types are called multipotent. Multipotent stem cells, mostly found in adult beings, are much harder to isolate, and thus available volumes for research are extremely low. Their developmental “flexibility” seems limited; however, recent findings in animals suggest these cells may be more flexible than previously thought. Umbilical cord stem cells fall into this category.

Pluripotent stem cells, in most cases isolated from human embryos a few days old, have the capability of becoming any type of cell in the body except those needed to completely develop a fetus. Pluripotent stem cells can be used to create pluripotent stem cell “lines” — cell cultures that can be grown indefinitely in the laboratory.

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