Stem cells regenerate lost or damaged cells. For example, when a person gives or loses blood, stem cells will replenish the supply. If the skin is damaged, it generates new skin cells as it heals. Since stem cells have the ability to generate new tissue specific cells, this area of medicine is often called “regenerative medicine”.
All animals, including humans, start from one cell, which results from fertilization of an egg by a sperm. The resulting one cell contains all of the animal's genetic material or DNA and is capable of developing into a complete organism. As the cell divides, the resulting cells or daughter cells, will still contain all of the DNA, while at the same time becoming specialized, and more restricted in their ability to become all types of organs and tissues.