When an egg is fertilized by a sperm to make a human embryo, that single fertilized egg cell divides millions of times to form the approximately six billion cells that make up the human body. These types of cells (4 to 7 day old embryo) are called embryonic stem cells that are unspecialized and have the ability to renew themselves and give rise to specialized cell types (they have not yet developed into cells that perform a specific function). A stem cell is uncommitted and remains that way, until it receives a signal to develop into a specialized cell, unlike a heart or muscle cell for example. Their differentiate capacity (they can divide and produce cells that have the potential to become specialized cell types or tissues) combined with the ability to become specialized makes stem cells unique and powerful. Stem cells are also capable of self-renewing, which means they are able to divide and self-reproduce themselves, but once a stem cell becomes specialized (differentiated), it is only able to produce the same type of cell. Researchers have for years looked for ways to use stem cells to replace cells and tissues that are damaged or diseased which gave attention to stem cells.
Research yielded the first look at a class of stem cells that can develop into any cell type in the body. This class of stem cells is called pluripotent, meaning the cells have the potential to develop almost all of the more than 200 different known cell types. These kinds of stem cells come from embryos and fetal tissue.
In 1998, for the first time, investigators were able to isolate this class of pluripotent stem cell from early human embryos and grow them in culture. Later evidence shows that these stem cells really are capable of becoming almost all of the specialized cells of the body meaning that they may have the potential to generate replacement cells for many types of tissues and organs (like heart, pancreas, nervous system, liver, lungs, brain, etc ),... [continues]
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