| Friday, August 18, 2006
| MAKING SENSE OF STEM CELLS
The most versatile stem cells come from embryos, meaning they are also the most controversial.
WHAT THEY ARE
Stem Cells are nature's master cells, capable of generating every one of the many different cells that make up the body. They have the ability to self-renew, which means that they are theoretically immortal and can continue to divide forever if provided with wnough nutrients. Because they are so plastic, they hold enormous promise as the basis for new treatments and even cures for disorders ranging from Parkinson's and heart disease to diabetes and even spinal-cord injury.
WHERE THEY COME FROM
LEFTOVER OR DEAD-END IVF EMBRYOS
Why are they useful. More than 400,000 embryos created during in vitro fertilization lie frozen in clinic tanks in the U.S. Many of them will be discarded, so the embryonic stem cells that exists inside them could be salvaged.
Drawbacks. The freezing process may make it harder to extract stem cells. Some of the embryos were the weakest ones created by infertile couples and may not yield high quality stem cells.
ADULT STEM CELLS
Why they are useful They exist in many major tissues, including the blood, skin and brain. They can be coaxed to produce more cells of a specific lineage and donot have to be extracted from embryos.
Drawbacks. They can generate only a limited number of cell types, and they are difficult to grow in culture.
Why they are used. Although they are primarily made up of blood stem cells, they also contains stem cells that can turn into bone, cartillage, heart muscle and brain and liver tissue. Like adult stem cells, they are harvested without the need for embryos.
Drawbacks. An umbilical cord is not very long and doesnt' hold enough cells to treat an adult.
Why they are useful These embryos are created using the technique that created Dolly the cloned sheep. Stem cells can be custom made by inserting a patient's skin cell into a hollwed human egg. Any resuklting therapies would not run the risk of immune rejection.
Drawbacks. The process has not yet been successfully completed with human cells, and it requires an enormous amount of fresh human eggs, whcih are official to obtain.
****** THE PROCESS ******
1. EMBRYO. An egg is fertilized or cloned to form an embryo. The embryo begins to divide.
2. ONE TO FIVE DAYS. The embryo divides into more and more cells and forms a hollow ball of cells called a blastocyst.
3. FIVE TO SEVEN DAYS. Embryonic stem cells begin to form along the inside of the blstocyst, creating the innner cell mass.
4. STEM LINE. The cells are scraped away and grown on a layer of feeder cells and culture medium.
could repair or replace a damaged heart.
Pancreatic Islet Cells
Could provide a cure for disbetes.
Could be used to treat Parkinson's spinal-cord injuries and strokes.
5. TISSUE PRODUCTION. Groups of stem cells are nurtured under specialized conditions, with growth factors that direct the cells to become any of the body's more than 200 vaious tissues.
(Source:TIMEMAG/SCIENCE by Nancy Gibbs)
|posted by infraternam meam @ 2:20 PM