Where Do Stem Cells Come From?

Stem cells refer to cells that can re-grow through mitotic cell division and differentiation through specialized cell types. They are found in the vast majority of multi-cellular organisms. Stem cells that occur naturally are broken into two categories for mammals: embryonic stem cells, and adult stem cells. While “stem cell research,” is a continual topic of discussion in the news, how much do you know about stem cells?

Adult stem cells, as their name suggests, are located within the stem cells of an adult organism, specifically within the tissues. The majority of adult stem cells are tissue specific. This means that they only produce the cells from the tissue that the adult stem cell is located within.

Since adult stem cells are located within adult tissues, there is considerably less controversy about researching from adult stem cells. This is because scientists can derive the stem cells from adult cell tissue samples so the answer to where do stem cells come from isn't controversial. This is remarkably different from destroying human embryos to access the embryonic stem cells, which is what some believe occurs when stem cells are harvested from aborted fetuses or from embryos.

Adult stem cells are able to renew indefinitely—thus, there is no cap on the amount of times they might self reproduce. They multiply through the process of cell division, and replace dying cells and regenerate to replace and fix damaged tissue.

What Is a Stem Cell?

There are three qualifications required for a stem cell to be considered a “stem cell.”

• First, the cell must be able to divide several times and yet still maintain its undifferentiated state (and thus sustain long term self renewal).
• Second, the cell must originally be an unspecialized cell.
• Third, the cell must be able to transform into a specialized cell.

The two categories of stem cells mentioned above—embryonic and adult stem cells—have all these qualities. These qualities are what allow the cells to develop into other tissues of the body, and are the reason why scientists and doctors are so interested in stem cell research. If other differentiated cells were able to behave as if they were stem cells, a scientist could create new muscle or tissue to replace failing cells.

Stem Cell Process

There are two different types of cell division that adult stem cells go through to complete the process of self renewal.

First, symmetric division results in two identical daughter cells. These daughter cells have the properties that make stem cells unique.

Asymmetric division then results in one cell with the properties of a stem cell, and one cell that is a progenitor cell. A progenitor cell is limited in its ability to self renew. The progenitors then go through a number of cell divisions until they differentiate into a mature cell. This is the process in which an adult stem cell can transforms into a tissue cell.

Embryonic Stem Cells

Embryonic stem cells come from different locations than adult stem cells. Embryonic stem cells are pluripotent stem cells which are derived from the inner cell mass of the blastocyst. Pluripotency means that there is one more potential outcome—any number of different cells can arise from the current cell.

The cells could differentiate into the ectoderm, endoderm, or mesoderm—which are the three significant skin layers. These categories consist of over two hundred different, more specific cell types, of a human being. A blastocyst is one of the earlier stages for an embryo. About four or five days after fertilization, a human embryo enters into the “blastocyst” stage and is about one hundred cells large.

Thus, stem cell research requires the embryo to be stunted in this stage, and not continue to develop. The diseases that might be able to be cured using these embryonic stem cells include, but are not limited to, the following: blindness, spinal cord injuries, juvenile diabetes, cancer, certain genetic diseases, and Parkinson’s disease.