Stem Cells 101 👉🏼There are four classes of stem cells: totipotent, multipotent, pluripotent, and unipotent
- Totipotent stem cells that develop into cells that make up all the cells in an embryo and fetus. (Ex: The zygote/fertilized egg and the cells at the very early stages following fertilization are considered totipotent.)
- Multipotent stem cells can give rise to multiple types of cells, but all within a particular tissue, organ or physiological system. (Ex: blood-forming stem cells/bone marrow cells, most often referred to as adult stem cells)
- Pluripotent stem cells (ex: embryonic stem cells) can give rise to any type of cell in the body. These cells are like blank slates, and they have the potential to turn into any type of cell. - Unipotent stem cells can self-renew as well as give rise to a single mature cell type. (Ex: sperm producing cells)
Embryonic stem cells are harvested from four to six-day-old embryos. These embryos are either leftover embryos in fertility clinics or embryos created specifically for harvesting stem cells by therapeutic cloning. Only South Korean scientists claim to have successfully created human embryos via therapeutic cloning and have harvested stem cells from them
Adult stem cells are already designated for a certain organ or tissue. Some adult stem cells can be coaxed into or be reprogrammed into turning into a different type of specialized cell within the tissue type - for example, a heart stem cell can give rise to a functional heart muscle cell, but it is still unclear whether they can give rise to all different cell types of the body
The primary role of adult stem cells is to maintain and repair the tissue in which they are found.