What Are Stem Cells?
Stem cells are undifferentiated cells that can change into specialized cells and divide to produce more stem cells. They are found in most organisms. In humans, there are two kinds of stem cells: embryonic stem cells and adult stem cells.
Embryonic stem cells are found in embryos and formed during the blastocyst phase of embryological development. They can change into all three primary germ layers: mesoderm, endoderm, and ectoderm.
Adult stem cells are found in the body after a baby is born. They are undifferentiated cells that divide to replace dying cells and regenerate damaged cells.
Stem cells are categorized by their potential to differentiate into other types of cells. Embryonic stem cells are the most potent because they can become every type of cell in the whole body. All stem cells are calcified into five5 different groups:
- Totipotent: The ability to change into all possible cell types. Examples are cells formed just after egg fertilization.
- Pluripotent: The ability to change into almost all cell types. Examples are embryonic stem cells.
- Multipotent: The ability to differentiate into closely related organs. Examples include hematopoietic (adult) stem cells and mesenchymal stem cells.
- Oligopotent: The ability to differentiate into a few different tissues. Examples include myeloid stem cells.
- Unipotent: The ability to only produce cells of their own type. Examples include skin stem cells.
Identification of Stem Cells
Identifying stem cells is a daunting task, and there is no complete agreement among scientists. Most tests are based on ensuring that stem cells are undifferentiated and capable of self-renewal.
Researchers and doctors are interested in stem cells for several reasons. When stem cells are instructed to specialize, they become very useful for regenerating damaged tissues. Researchers and doctors are seeking accessible sources of adult stem cells in humans. The most used and most accessible stem cells are:
- Bone marrow, which requires drilling into bone to harvest stem cells
- Adipose tissue, which requires liposuction to harvest stem cells
- Umbilical cord, which is easily and painlessly harvested. Two kinds of stem cells are found in the umbilical cord. Mesenchymal stem cells are found in Wharton’s jelly, and the cord blood is rich in hematopoietic stem cells. Both mesenchymal stem cells and hematopoietic stem cells are generally characterized by their potency to differentiate into different cell types like bone, muscle, skin, etc.