Stem cells. That is the term that brings hope for a new revolution in medicine. One day, some think, doctors will be able to grow new organs in the lab, on demand, for patients instead of waiting for donors. The concept of an organ donor might fade out of public awareness because it will no longer be needed in developed countries. Virtually any tissue damage in the body will be easily healed. Nerve damage, especially that of the spinal cord, will be mended without worry of paralysis. Collapsed lungs could be replaced with new ones. Faulty hearts could be switched with ones that have been carefully grown in controlled laboratory environments. In fact, any organ could be replaceable if we can ever fully understand and utilize stem cells. Additionally, patients will not need immunosuppressive drugs to protect their new organs. Just what are stem cells, anyway?
In the earliest stage of gestation, a baby (an embryo at this time) is made up entirely of cells that serve no function except to multiply. These are embryonic stem cells. An embryo's cells are constantly dividing so the baby can grow. At some point, the cells start to differentiate, or decide what functions they will perform in the fully formed baby's body. Some stem cells will become heart cells, some nerve cells, and still others will become bone cells. Every tissue in the body needs cells that are specialized for specific functions. This is a remarkable feat: one type of cell changes into every other type needed for the body to work.
After birth, there are some remaining stem cells that will be present into adulthood. Stem cells found throughout an adult body are called adult or somatic stem cells. These cells are naturally used by the body for producing specialized cells, developing tissues during adolescence, and healing injuries.
So, what is stopping us from using stem cells to make new organs? Harvesting them is one problem. Obtaining stem cells from an embryo means destruction of it, considered by many to be the death/murder of a baby. Adult stem cells are ethically permissible, but they are more difficult to harvest (like extracting bone marrow) and less abundant. Stem cells are present in amniotic fluid and umbilical cord blood, but these are conventionally disposed of after birth. Another way to get stem cells could be reversing the differentiation process. Some scientists have been able to turn skin cells into stem cells.
Another problem is successfully utilizing stem cells. Embryonic stem cells are pluripotent, meaning they can differentiate into any type of cell. Many adult stem cells are merely multipotent, meaning they can only differentiate into a limited selection of cell types. Embryonic stem cells, if they come from someone other than the patient, can pose a similar risk as donor organs. A new heart is not so great if the immune system tries to destroy it. Ideally, a patient's replacement organs would be grown from his/her own stem cells. Another risk is that of tumor formation. After all, cancer is characterized by cells that stop performing their designated functions and rampantly multiply.
Once we gain mastery over stem cells, we should reap great benefits. And scientists are making significant progress. Blindness by macular degeneration is being experimentally treated with retinal cells that were grown from stem cells. Multiple gels have been developed that stimulate the body's stem cells into action for greater healing ability than is normally possible. Tracheas, or windpipes, have been grown from patients' adult stem cells and transplanted successfully in Europe. Dentistry might someday be changed, too. Mice have had new teeth grown from stem cells and transplanted. Imagine future senior citizens that, while they are chronologically quite elderly, have organs that are as biologically youthful as their grandchildren.
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