Stem Cells: 11 Questions and Answers

Stem cells are tiny, but they draw big-time attention from scientists, patients, lawmakers, celebrities, and people of every other background.

Stem cell headlines are a hive of buzzwords -- "embryonic" this and "adult" that -- as well as controversy.

But you needn't be a PhD to understand the basics of stem cells.

If you think of your body as a car, so far doctors have had the ability only to repair a defective part or, at best, take a part out of another car and put it into you (organ transplantation). Stem cells can theoretically grow and develop into any spare part you need, so it is as if the doctor can just call the car manufacturer and get the original replacement part. As you can imagine, this could have the potential to cure a tremendous number of diseases.

The main reason there is a big debate over the use of stem cells is that these cells can come from an embryo. To many people, an embryo is a living human being and destroying an embryo for any reason is morally unacceptable. People on the other side of the debate say that embryonic stem cells have the potential to cure many diseases and the embryos used would have been discarded by fertility clinics anyway.

Leaving the ethical debate behind, here is what we know – and what we don't know -- about stem cells. Just the medical facts, ma'am.

Q: What are stem cells?

A: All of us start from a single cell formed at conception, when a sperm cell joins with an egg. This cell then starts dividing and forms a ball of cells. About four days after conception, this ball of stem cells starts changing its shape, and individual cells in that ball start changing and becoming different from their neighbors. At this time, the ball of cells is smaller than a pinpoint. This process, called differentiation, allows some cells to become liver cells and other cells to become nerve cells or skin cells and so on.

This process is similar to the way in which a plant grows. In the beginning, a stem grows out of the seed you planted, which then has branches, and eventually leaves, fruits, and flowers grow on those branches.

These earliest "stem" cells in the embryo give rise to all the different cells in the body.

Adult Stem Cells vs. Embryonic Stem Cells

Q: What's the difference between adult stem cells and stem cells taken from an embryo?

A: Embryonic stem cells are stem cells that you take from an embryo, and adult stem cells are stem cells you take from a person (adult or child) or from the umbilical cord.

Scientists have found that a few stem cells persist even after we are born. It seems that these adult cells are a kind of backup, so if a particular kind of cell needs replacing, the adult stem cells can differentiate and form those cells. Most adult stem cells can form a limited number of cell types.