A stem cell is a "generic" cell that can make exact copies of itself indefinitely. In addition, a stem cell has the ability to produce specialized cells for various tissues in the body -- such as heart muscle, brain tissue, and liver tissue. Scientists are able to maintain stem cells forever, developing them into specialized cells as needed.

There are two basic types:

• Embryonic stem cells - these are obtained from either aborted fetuses or fertilized eggs that are left over from in vitro fertilization (IVF). They are useful for medical and research purposes because they can produce cells for almost every tissue in the body.

• Adult stem cells - these are not as versatile for research purposes because they are specific to certain cell types, such as blood, intestines, skin, and muscle. The term "adult stem cell" may be misleading because both children and adults have them.

Potential uses for stem cells

There are many areas in medicine in whch stem cell research could have a significant impact. For example, there are a variety of diseases and injuries in which a patient's cells or tissues are destroyed and must be replaced by tissue or organ transplants. Stem cells may be able to generate brand new tissue in these cases, and even cure diseases for which there currently is no adequate therapy. Diseases that could see revolutionary advances include Alzheimer's and Parkinson's disease, diabetes, spinal cord injury, heart disease, stroke, arthritis, cancer, and burns.

Stem cells could also be used to gain a better understanding of how genetics work in the early stages of cell development. This can help scientists understand why some cells develop abnormally and lead to medical problems such as birth defects and cancer. By understanding the genetic basis for cell development, scientists may learn how to prevent some of these diseases.

Finally, stem cells may be useful in the testing and development of drugs. Because stem cells can be used to create unlimited amounts of specialized tissue, such as heart tissue, it may be possible to test how drugs react on these specialized tissues before trying the drugs on animals and human subjects. Drugs could be tested for effectiveness and side effects more rapidly.

Controversy about stem cell research

In August 2001, President George W. Bush approved limited federal funding for stem cell research. While stem cell research has the potential to provide major medical advances, including cures for many diseases, stem cell research is controversial.

The stem cell controversy is based on the belief by opponents that a fertilized egg is fundamentally a human being with rights and interests that need to be protected. Those who oppose stem cell research do not want fetuses and fertilized eggs used for research purposes. However, a team of scientists have developed a technique that was successful in generating mouse stem cells without destroying the mouse embryo. This technique has not yet been attempted on human embryonic tissue. Many other scientists are attempting to create more universally accepted forms of human embryonic stem cells, as well as other types of adult stem cells.

Supporters of stem cell research argue that the fertilized eggs are donated with consent from each couple and would be discarded anyway. Therefore, there is no potential for those fertilized eggs to become human beings. Fertilized eggs are not (at this time) being created specifically for stem cell research.

As with any moral and ethical issue, the controversy surrounding stem cell research will likely continue for quite some time.

The U.S. government released new stem cell guidelines in 2009. The new guidelines cover issues such as informed consent of donors and the wording of consent, as well as the issue of financial gain. The National Institutes of Health (NIH) maintains a register of stem cells, including human embryonic lines, that are eligible for government funding.

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