What are Stem Cells

What are stem cells? Stem cells are unspecialized cells in the body that constantly divide to form a pool of cells that can then specialize when they are needed. When we have the union of the sperm and the egg to produce one cell, this in turn divides into a form called morula. The morula contains identical cells all of which are totipotent. This means that any single cell in the morula can divide and become virtually any cell in the human body, including embryonic tissue and placenta. The big change comes when it divides.

In the blastocyst, the cells become more specialized, but they still retain some potential to differentiate into almost any of the cells of the body, except some specialized ones like the placenta.

What we’re interested in is in what happens from here on. With each division, cells can differentiate from its parents and specialize more and more. They loose a little bit of their power to become anything. They go from pluripotent to multipotent. Multipotent cells are specialized cells which nonetheless have the ability to become a variety of cells. The multipotent hematopoietic cell, for example, which is the cell that forms blood elements, can become very varied elements in the blood.

These multipotent cells have the ability of maintaining an undifferentiated state.

Look at the picture. If a stem cell undergoes mitosis, it divides and produces two daughter cells. One of the daughter cells is exactly like the original stem cell. This one maintains the pool of stem cells from which to get new cells all throughout our lives. The other cell goes on to differentiate, going different pathways to become anything except a placenta or other early embryonic tissues.

When a cell goes all the way through a pathway, it can’t go back. This means that it cannot divide again and become less differentiated.

The ultimate stem cells are embryonic stem cells. They are totipotent. They can become any cell in the organism. At about the tenth day stage after fertilization there are several dozens of these undifferentiated totipotent cells in a human embryo. These cells can be removed from the embryo, grown in a laboratory dish and reproduced. In 1998, James Thomson at the University of Wisconsin showed that this is possible to do. Put them in a laboratory dish and they would grow indefinitely as a laboratory culture.

In laboratory experiments on animals, these embryonic stem cells can be induced to form many different cell types. In animals, these cell types coming from embryonic stem cells have cured brain damage, heart damage, muscle damage, etc. This has generated great excitement for their potential in human medicine.

The proposal is to use laboratory grown stem cells as a supply. You don’t need a lot of embryos to do this. The problem is that if I get some stem cells from someone else, they’re not mine. Those cells going into my heart would do the work, but then my immune system would ultimately reject them.

This has led to the proposal of therapeutic cloning. This is the subject of another article.