Just like a seed that grows in a tree, stem cells are the starting point of a waterfall of division that produce millions of special cells in the skin, muscles, blood, brain, eyes, heart and other organs that make up our body. The youngest stem cells that are obtained from embryos only days old have the greatest potential. These cells called embryonic stem cells are the seed; they can do anything – they grow to be the tree. The specialized stem cells are obtained from the seed so as to create the branches and even more specialized cells create the leaves and fruits and even more seeds. This same potential exists in the human body, making it possible to grow stem cells to replace all types of diseased organs and tissues.
Embryonic stem cells are “pluripotent”, which means that they are capable of growing into any type of cell. Older embryonic stem cells or adult stem cells are “multipotent” which means that they still are capable of growing into various types of cells but are wired to make specialized tissues such as the nervous system, vascular circulation or muscles. In other words, multipotent cells (also called adult stem cells) somehow have been already told or have already decided what their identity is going to be, and they continue along this defined path for making some type of tissue or organ – say, the blood system, for example. As the pregnancy advances, the stem cells become more and more specialized.
Some interesting links:
The official National Institutes of Health resource for stem cell research
The Harvard Stem Cell Institute
Translation by Eugenia Gutierrez Ortiz Mena – Genesis Translations