Stem cells may be found in all animals from early stages of development as an embryo until the end of life. There are several types of stem cells depending on their source and potency.
1. Based on source of stem cells-
Adult Stem Cells-
The primary role of adult stem cells in humans is to maintain and repair the tissue in which they are found. While we call them adult stem cells, they are more accurately called somatic (from the Greek word soma = body) because they come virtually any body tissue, not only in adults but children and babies as well.
Adult type stem cells come from:
Umbilical Cords, Placentas and Amniotic Fluid—Adult type stem cells can be derived from various pregnancy-related tissues.
Body Tissues—In adults and children, from the moment we're born, stem cells are present within virtually all tissues and organ systems.
Cadavers—Neural stem cells have been removed from specific areas in post-mortem human brains as late as 20 hours following death.
Adult stem cells are a “natural” solution. They naturally exist in our bodies, and they provide a natural repair mechanism for many tissues of our bodies. They belong in the microenvironment of an adult body, while embryonic stem cells belong in the microenvironment of the early embryo, not in an adult body, where they tend to cause tumors and immune system reactions.
Most importantly, adult stem cells have already been successfully used in human therapies for many years. New therapies using adult type stem cells are being developed all the time.
Embryonic stem cells-
Embryonic stem cells are derived from a four- or five-day-old human embryo that is in the blastocyst phase of development. The embryos are usually extras that have been created in IVF (in vitro fertilization) clinics where several eggs are fertilized in a test tube, but only one is implanted into a woman.
Sexual reproduction begins when a male's sperm fertilizes a female's ovum (egg) to form a single cell called a zygote. The single zygote cell then begins a series of divisions, forming 2, 4, 8, 16 cells, etc. After four to six days - before implantation in the uterus - this mass of cells is called a blastocyst. The blastocyst consists of an inner cell mass (embryoblast) and an outer cell mass (trophoblast). The outer cell mass becomes part of the placenta, and the inner cell mass is the group of cells that will differentiate to become all the structures of an adult organism. This latter mass is the source of embryonic stem cells - totipotent cells (cells with total potential to develop into any cell in the body).
In a normal pregnancy, the blastocyst stage continues until implantation of the embryo in the uterus, at which point the embryo is referred to as a fetus. This usually occurs by the end of the 10th week of gestation after all major organs of the body have been created.
However, when extracting embryonic stem cells, the blastocyst stage signals when to isolate stem cells by placing the "inner cell mass" of the blastocyst into a culture dish containing a nutrient-rich broth. Lacking the necessary stimulation to differentiate, they begin to divide and replicate while maintaining their ability to become any cell type in the human body. Eventually, these undifferentiated cells can be stimulated to create specialized cells.
Sexual reproduction begins when a male's sperm fertilizes a female's ovum (egg) to form a single cell called a zygote. The single zygote cell then begins a series of divisions, forming 2, 4, 8, 16 cells, etc. After four to six days - before implantation in the uterus - this mass of cells is called a blastocyst. The blastocyst consists of an inner cell mass (embryoblast) and an outer cell mass (trophoblast). The outer cell mass becomes part of the placenta, and the inner cell mass is the group of cells that will differentiate to become all the structures of an adult organism. This latter mass is the source of embryonic stem cells - totipotent cells (cells with total potential to develop into any cell in the body).
In a normal pregnancy, the blastocyst stage continues until implantation of the embryo in the uterus, at which point the embryo is referred to as a fetus. This usually occurs by the end of the 10th week of gestation after all major organs of the body have been created.
However, when extracting embryonic stem cells, the blastocyst stage signals when to isolate stem cells by placing the "inner cell mass" of the blastocyst into a culture dish containing a nutrient-rich broth. Lacking the necessary stimulation to differentiate, they begin to divide and replicate while maintaining their ability to become any cell type in the human body. Eventually, these undifferentiated cells can be stimulated to create specialized cells.
2. Based on ability to regenerate (potency)-
Totipotent-
the ability to differentiate into all possible cell types. Examples are the zygote formed at egg fertilization and the first few cells that result from the division of the zygote.
Pluripotent-
the ability to differentiate into almost all cell types. Examples include embryonic stem cells and cells that are derived from the mesoderm, endoderm, and ectoderm germ layers that are formed in the beginning stages of embryonic stem cell differentiation.
Multipotent-
the ability to differentiate into a closely related family of cells. Examples include hematopoietic (adult) stem cells that can become red and white blood cells or platelets.
Oligopotent-
the ability to differentiate into a few cells. Examples include (adult) lymphoid or myeloid stem cells.
Unipotent-
the ability to only produce cells of their own type, but have the property of self-renewal required to be labeled a stem cell. Examples include (adult) muscle stem cells.
3. Other type of stem cell-
Amniotic Stem Cells-
amniotic stem cell
These are stem cells found in the amniotic fluid. These stem cells are very active and can proliferate without feeders. In addition, unlike embryonic stem cells they do not cause tumors. These can be made into fat cells, bone cells, muscle cells, blood vessel walls, liver and nerve cells.
Induced Pluripotent Stem Cells-
Induced pluripotent stem cells are a type of pluripotent stem cell artificially derived from a non-pluripotent cell - typically an adultsomatic cell - by inducing a "forced" expression of specific genes.These are not adult stem cells but are created from adult skin cells after genetically programming them to become pluripotent stem cells.
Fetal-
fetal stem cells
The primitive stem cells located in the organs of fetuses are referred to as fetal stem cell.
Cord blood-derived multipotent stem cell-
Cord blood-derived multipotent stem cells (CB-SCs) are a type of multipotent stem cell from mammalian cord blood. They are identifiable by their ability to attach to the plastic surface of non-tissue cultured-treated Petri dishes. CB-SCs are the active agent in stem cell educator therapy, which has therapeutic potential against autoimmune diseases. Pre-clinical studies and clinical trials have demonstrated the therapeutic potential of CB-SCs in type 1 diabetes