Stem Cells (cont.)

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Fetal stem cells

The embryo is referred to as a fetus after the eighth week of development. The fetus contains stem cells that are pluripotent and eventually develop into the different body tissues in the fetus.

Adult stem cells

Adult stem cells present in all humans in small numbers. The adult stem cell is one of the class of cells that we have been able to manipulate quite effectively in the bone marrow transplant arena over the past 30 years. These are stem cells that are largely tissue-specific in their location. Rather than typically giving rise to all of the cells of the body, these cells are capable of giving rise only to a few types of cells that develop into a specific tissue or organ. They are therefore known as multipotent stem cells. Adult stem cells are sometimes referred to as somatic stem cells.

The best characterized example of an adult stem cell is the blood stem cell (the hematopoietic stem cell). When we refer to a bone marrow transplant, a stem cell transplant, or a blood transplant, the cell being transplanted is the hematopoietic stem cell, or blood stem cell. This cell is a very rare cell that is found primarily within the bone marrow of the adult.

One of the exciting discoveries of the last years has been the overturning of a long-held scientific belief that an adult stem cell was a completely committed stem cell. It was previously believed that a hematopoietic, or blood-forming stem cell, could only create other blood cells and could never become another type of stem cell. There is now evidence that some of these apparently committed adult stem cells are able to change direction to become a stem cell in a different organ. For example, there are some models of bone marrow transplantation in rats with damaged livers in which the liver partially re-grows with cells that are derived from transplanted bone marrow. Similar studies can be done showing that many different cell types can be derived from each other. It appears that heart cells can be grown from bone marrow stem cells, that bone marrow cells can be grown from stem cells derived from muscle, and that brain stem cells can turn into many types of cells.

Medically Reviewed by a Doctor on 1/23/2014

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