ALS website concerning stem cell research [LINK]
From their site -
Overview
The discovery that human embryonic stem cells can be isolated and propagated in the lab with the potential of developing into all tissues of the body is a major medical breakthrough. But it has raised ethical concerns. Stem cells are also present in adults, scientists now find. If there were a way to stimulate resident stem cells to replace dying cells, the limitations of transplantation could be overcome, as well as the ethical issues.
What are the types of embryonic stem cells?
Human embryonic stem cells are derived from fertilized embryos less than a week old. When a sperm fertilizes an egg and creates a single cell, this cell has the potential to form a complete organism. In the first hours after fertilization, this cell divides into identical, so-called totipotent cells. After approximately four days, the cells start to specialize and form a hollow sphere of cells called a blastocyst.
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The discovery that human embryonic stem cells can be isolated and propagated in culture with the potential of developing into all tissues of the body is a major medical breakthrough. However it has raised a great deal of ethical questions.
Adult stem cells vs. embryonic stem cells
Stem cells are important in early human development, yet they persist into adulthood. The presence of bone marrow stem cells in adults has been known for a long time. These stem cells give rise to all cells of the blood system. More recently, stem cells have been discovered in the adult brain and spinal cord. There are several approaches now in human clinical trails that utilize adult stem cells (such as blood forming cells and cartilage forming cells).
However, because adult cells are already specialized, their potential to regenerate damaged tissue is more limited. Another limitation is their inability to proliferate in culture. Therefore, obtaining clinically significant amounts of adult stem cells may prove to be difficult.