| What Are Stem Cells?
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. Seattle Pacific University
Associate Professor of Biology Cynthia Fitch provides this clarification
of what is meant by the term “stem cells”:
embryo has reached the “blastocyst” stage, when stem cells could
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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