Stem cells can be defined as unspecialized cells that have the ability to self regenerate and the ability to differentiate into other cells. Commonly these cells originate from two main sources that are mentioned below:
- Embryos formed during the blastocyst phase of embryological development (embryonic stem cells)
- Adult tissue (adult stem cells)
Both the types of cells are characterized by their potential or potency to differentiate into different type of cells. (like muscle, skin, bone, etc)
Stem cells can be categorized by their potential difference into other types of cells. Embryonic stem cells are the most potent cells as these can become every type of cells present in our body. The classification is as follows:
- Totipotent: It’s the ability of the cells to differentiate into different types of cells. For example; the zygote formed at egg fertilization and the first few cells that are formed from the division of zygote.
- Multipotent: It is the ability of the cells to differentiate into a closely related family of cells. For example- hematopoietic (adult) stem cells which becomes red and white blood cells or platelets.
- Pluripotent: The cells can differentiate into different cell types. For example- embryonic cells and stem cells that are derived from the endoderm, mesoderm and ectoderm germ layers, which are formed at the beginning of embryonic stem cell differentiation formation.
- Obligopotent- The ability of the cells to differentiate into few cells. Example -lymphoid or myeloid stem cells.
- Unipotent – It is the ability of the cells to produce cells of their own type but also have the property of self renewal that is required to be labeled as stem cells. Examples- (adult) muscle stem cells.
Among all the stem cells, embryonic cells are considered as pluripotent instead of totipotent. This is so because they can not become a part of the extra-embryonic membranes or the placenta.