Stem Cells

Research on stem cells is advancing knowledge about how an organism develops from a single cell and how healthy cells replace damaged cells in adult organisms. Stem cells are also researched because scientists want to investigate the possibility of cell-based therapies to treat diseases like Parkinson's disease. Stem cells have two important characteristics that distinguish them from other types of cells. First, they are unspecialized cells that renew themselves for long periods through cell division. The second characteristic is that under certain physiologic or experimental conditions, they can become cells with special functions such as the beating cells of the heart muscle or the insulin-producing cells of the pancreas. Scientists work with two kinds of stem cells, embryonic stem cells and adult stem cells. They both have different functions and characteristics. Embryonic stem cells are undifferentiated cells from the embryo that have the potential to become a wide variety of specialized cell types. Adult stem cell is an undifferentiated cell found in a differentiated tissue that can renew itself and (with certain limitations) differentiate to yield all the specialized cell types of the tissue from which it originated. Many years of detailed study of the biology of mouse stem cells led to the discovery, in 1998, of how to isolate stem cells from human embryos and grow the cells in the laboratory. These are human embryonic stem cells. Embryonic stem cells (ES cells) are stem cells derived from the inner cell mass of a blastocyst. A blastocyst is an early stage embryo- approximately 4 to 5 days old in humans and consisting of 50-150 cells. ES cells are pluripotent (meaning to have more than one potential outcome), and give rise during development of all derivatives of the three primary germ layers: ectoderm, endoderm and mesoderm. In other words, they can develop into each of the more than 200 cell types of the adult body when given sufficient and necessary stimulation for a specific cell type. They do not contribute to the extra-embryonic membranes or the placenta. The use of adult stem cells in research and therapy is not as controversial as embryonic stem cells, because the production of adult stem cells does not require the destruction of an embryo. The government will not provide funding for embryonic stem cell research but are willing to provide funding for research on adult stem cells. There exists a widespread controversy over stem cell research that emanates from the techniques used in the creation