A stem cell is a single cell found in all living organisms. Stem cells have the ability to change into different types of specialized cells needed to build and repair living organisms. There are two types of stem cells: embryonic stem cells and adult stem cells. These two types can be divided into two groups: undifferentiated cells that are able to generate into any form of tissue and tissue specific cells that have already developed to form a specific tissue type. Human life actually begins with stem cells that divide and define the different cells of the human body. Life depends on these stem cells.
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1. Undifferentiated embryonic stem cells are found in living embryos. The undifferentiated cells are found in the early process of development of a fetus. The fertilized egg divides into two cells then four then eight and so on until there are about 150 cells. At this point of development the group of cells is called the blastocyst. The blastocyst contains two types of cells: the trophoblast and the inner cell mass. Undifferentiated embryonic stem cells are found in the inner cell mass.
2. Tissue specific embryonic stem cells are found in the umbilical blood of a newborn. A small number of stem cells can also be found in the fetal tissue. In order to obtain enough cells to be useful, these cells are extracted and cultured in the laboratory where they can multiply. Recent research has found stem cells in the amniotic fluid and teeth (which are still beneath the gums) of newborns at this point are not useful.
3. Adult stem cells are only tissue specific cells that are used by the body to reproduce certain tissues or components of the body. One specific adult stem cell is found in the bone marrow. These cells are used to form new blood cells, blood vessels, bone, cartilage and muscle.
4. All stem cells used for research and therapies are found in certain laboratories and research facilities throughout the world. In order to obtain the number of stem cells needed they must be allowed to reproduce and multiply in the laboratory without changing their composition. Small amounts of stem cells are extracted from the source and placed into a culture dish lined with mouse embryonic skin cells that supply nutrients to the stem cells. The cultures are kept in specialized incubators until enough cells are present to be used.
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