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According to medical science, all animals including humans start from one cell, which results when the sperm fuses with
the egg. That one cell contains the animal’s entire DNA and is capable of developing into a complete organism. With progressive
cell divisions, the daughter cells will still contain the entire DNA, but they become more specialized, and more restricted in
their capacity to develop into all types of organs and tissues. Some daughter cells, however, do retain the capacity to
regenerate tissue if it is injured or depleted.
When a person gives or loses blood, for example, stem cells will replenish the supply. If the skin is damaged, it
generates new skin cells as it heals. The liver, too, contains stem cells that allow it to regenerate injured areas,
and it has been recently found that bone marrow contains stem cells capable of forming liver cells.
The procedure often called a "bone-marrow transplant" is in fact stem-cell therapy. While controversial in the
treatment of breast cancer, it is accepted as therapy in a variety of blood diseases such as leukemias and aplastic
anemia. Stem cells also play a great role in human organ transplantation, helping the new organs take hold. Fetal
neuronal cells injected into the brains of patients with Parkinson's disease have produced sometimes dramatic, if
somewhat uneven, results. There are many proven evidences for such cases.
Stem cells are currently obtained in one of three ways. They can be obtained from tissues within an aborted fetus,
from embryos donated through in vitro fertilization programs, and from adult tissues.
Generally stem cells are obtained from tissue, which has been removed during terminated pregnancies,
or from embryos produced by in-vitro fertilization clinics. Once isolated properly, the cells can be grown
up in the laboratory and stored for future use. Each reservoir of cells, derived from a single embryo, is
known as a cell line. A more reliable supply would be obtained by copying or cloning embryos specifically for
their stem cells.
However, each method and source seems to have its own pros and cons. If it became possible to take
the cells of an adult with a particular disease and grow them in culture to regenerate organs
or tissues, the problems of rejection would be solved. If, of course, the organ damage was the result
of a genetic disease, the regenerated organs or tissues would have the same disease—that is the problem.
On the negative side, no one has yet succeeded in growing stem cells obtained from adult tissues for
very long. And so far they don't seem to have the same capacity to differentiate into the variety of different
cell types that embryos can.
Fortunately, stem cells obtained from embryos and fetuses, on the other hand, have been grown for
many generations—perhaps they can be grown indefinitely—and they are capable of differentiating into a
large number of cell types. One disadvantage is that during culture in the laboratory they try to spontaneously
differentiate into specialized tissues when such differentiation is not wanted. But at this issue there is growing
concern over research and funding, because there have been few instances where embryos were created for the purpose
of research. As far as law goes, it differs from country to country—US the strictest to UK the most liberal.
Almost everyone is against the misuse of this great invention. So for the sake of humanity and human ethics,
we all must take pledge to use the right approach.
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