Our bodies are made up of trillions of small units, known as cells. However, at the very early phase of development, we were embryos consisting of only a tiny clump of cells. Cells in an embryo are in a primitive state, and we call them embryonic stem cells. Embryonic stem cells can develop into three types of cells, called ectodermal stem cells, endodermal stem cells, and mesodermal stem cells. These three types of stem cells then go on to form 200 different types of cells. For example, stem cells form the cells of your skin, the red blood cells in your blood, and the cells that produce the color of your eyes. Altogether, stem cells form all the organs and tissues in the body, such as the bones, kidneys, liver, blood, and brain. After birth, embryonic stem cells are no longer present in the body.
However, even in the bodies of children, adults, and elderly people, we find several types of stem cells. These stem cells can form some, but not all, of the 200 different cell types.

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