One of the goals of this blog is to increase scientific literacy. After writing the post above, I thought this might be a good opportunity to talk a bit more about stem cells. What are stem cells, anyway? Without stem cells, wounds would never heal, your skin and blood could not continually renew themselves, fertilized eggs would not grow into babies, and babies would not grow into adults. Stem cells are quite unlike the specialized, or differentiated, cells in your body — such as the nerve cells, muscle cells and blood cells that enable you to function. In contrast, stem cells are the body's silent reserves. They spring into action when you need replace cells in your body. For example, due to the acid used to digest food, stem cells are needed to constantly replace the lining of your stomach.
A fertilized egg is the ultimate stem cell, as it is the source of every type of cell in the body (also known as "totipotent"). Within three to six days after a human egg is fertilized, it has grown into a ball of a few hundred cells called a blastocyst (which is smaller than the period at the end of this sentence). Within this ball lie a small number of cells that will go on to develop into the embryo (the rest form the placenta and other supportive tissues). These are known as embryonic stem cells, and they have the potential to produce all the cell types in the human body (what we call "pluripotent"; these cells can form every cell type, but not placenta). This is what makes them so valuable.
Scientists hope to use stem cells to replace or rejuvenate damaged tissue (which is what was done in the post above).
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