Adult stem cells
Adult stem cells are cells distributed through various kinds of tissue which can differentiate into cells specific to the tissue in which they are located. Their main role is to replace damaged cells.
Origin of adult stem cells
The origin of adult stem cells is not certain in all cases. They are found in most tissue, brain, muscle, cardiovascular, etc.
Plasticity of adult stem cells
It was long thought that the ability for adult stem cells to differentiate into multiple types of cells was limited by the tissue in which they were located. For example, muscle stem cells would only differentiate into muscle cells and those in the brain would only differentiate into neurons. There is, however, evidence that if a stem cell from one tissue is transplanted to another tissue, it can differentiate into cells endemic to the new tissue.
Embryonic stem cells
Embryonic stem cells come from the inner part of the blastocyst. They can transform into any cell except for those that make up the what is derived from the outer layer of the blastocyst, or the trophoblast. This has made them important in medical research involving using stem cells to regenerate and repair organs and tissue.
Origin of embryonic stem cells
Embryonic stem cells are derived from the earliest stages of the embryo. During sexual reproduction, a sperm will fertilize an ovum and the two will become one cell called a zygote. The zygote will begin to divide and, over several days, a cluster of cells will form called a blastocyst. The blastocyst consists of two layers: the embryoblast and the trophoblast. The trophoblast is the outer part of the blastocyst which will become part of the placenta. The embryoblast will eventually become the body and organs of the adult organism. It is from this inner part of the blastocyst that embryonic stem cells are found.
Stem cells have varying abilities to differentiate into different kinds of cells. Some cells can transform into any possible cell within the body of the organism while others will only be able to become specific types of cells. Biologists have classified stem cells according to how potent they are or the diversity of cells into which they can transform.
- Totipotent – cells that are totipotent can transform into any possible cell within the body of a given organism. Examples of totipotent cells include the zygote and the first generation of cells after the zygote divides.
- Pluripotent – cells of this type can divide into most types of cells but not all. Embryonic stem cells are in this category since, although they can transform into all body cells, they cannot become cells that are a part of the placenta or other parts derived from the trophoblast.
- Multipotent – cells of this type can transform into a group of closely related cells. Examples of these include stem cells associated with the blood stream that can transform into any type of blood cell but not muscle cells or other nonblood cells.
- Oligopotent – cells of this type are even more limited in their ability to divide into different kinds of cells. they will form into a few specific cell types within a particular tissue though not all. Examples of these cells include hematopoietic stem cells.
- Unipotent – cells that are unipotent only differentiate into cells of one type. This would include muscle cells.
Among stem cells, the most potent stem cell is the embryonic stem cell since it can differentiate into any kind of cell at any location in the body.
Similarities between adult and embryonic stem cells
Embryonic and adult stem cells are both capable of differentiating into a variety of cells to repair or develop an organism. They are also somewhat limited in what types of cells their division can produce.
Although embryonic stem cells can still divide into any cell from tissue that originates from the inner part of the blastocyst, they cannot become cells that make up the trophoblast or outer part of the blastocyst. Thus, they do have limited potency like adult stem cells.
Differences between adult and embryonic cells
Despite the similarities, there are also significant differences
- Embryonic cells can become any cell independent of the part of the organism in which they reside. Adult stem cells usually only form into the cells specific to the tissue in which they are located, although adults stem cells will transform into different types of cells if they are transplanted into different tissues. As a result, embryonic stem cells are classified as pluripotent whereas adult stem cells are multipotent, oligopotent, or unipotent.
- The origin of embryonic stem cells is well known whereas the origin of adult stem cells is not as well understood in all tissues.
- Embryonic stem cells are found only in the embryonic stage whereas adult stem cells are found in the organism after its tissues have differentiated
- There is only one type of embryonic stem cell whereas there are many types of adult stem cells which have different characteristics and varying degrees of potency
Adult vs. embryonic stem cells
Adult stem cells are cells found in various tissues that can differentiate into cells specific to a particular tissue. Their main role is to replace damaged or missing cells. They can also transform into different types of cells other than those associated with the tissue in which they reside if they are transplanted from the original tissue to a different tissue, but what cells they transform into is dependent on the tissue in which they are located. Embryonic stem cells are stem cells found in the inner part of the blastocyst. They can differentiate into any cell that will make up the later organs and body of the adult organism. They are, however, still limited in that they will not become cells that are derived from the outer part of the blastocyst. They are also only found in the embryo and there is only one type, whereas there are many types of adult stem cells and they are found in many tissues of the adult organism
Author: Caleb Strom
Caleb Strom has a B.SC. in earth science from the University of California San Diego and is currently a graduate student in geological sciences at California State Polytechnic University Pomona. He has done scientific research in planetary science at the Scripps Institution of Oceanography and astrophysics at the Center for Astrophysics and Space Science at UC San Diego.