Stem Cell Basics
Scientists work with two different types of stem cells, embryonic stem cells and adult stem cells. Embryonic stem cells are derived from embryos, more specifically, embryos that developed from eggs that were fertilized through in vitro fertilization at an in vitro fertilization clinic and then donated for research purposes. These human embryonic stem cells are usually four to five days old and are a hollow microscopic ball of cells called the blastocyst. The blastocyst is made up of three structures, which include the trophoblast, blastocoel, and inner cell mass. The trophoblast is the layer of cells surrounding the blastocyst. The blastocoel is the hollow cavity found within the blastocyst. Finally, the inner cell mass is a group of roughly 30 cells found at one end of the blastocoel. Adult stem cells are unspecialized cells found among differentiated cells in a tissue or organ within the body. Adult stem calls can renew themselves, and can become specialized to meet the needs of the reduced number of cells within that specific tissue or organ at any time. Adult stem cells are used by the body to maintain and repair tissue in which they are found. Although they have been identified in many organs and tissues, adult stem cell numbers are very small within each specialized tissue. These cells reside in a specific area within the tissue and remain unspecialized for many years until activated by some stimulus such as disease or tissue damage. Adult stem cells have been found in the brain, bone marrow, blood vessels, skeletal muscle, skin, and liver in the human body.
Because of their unique, unspecialized characteristic, human stem cells have remarkable potential to develop into many different cell types in the body. Through cell division, stem cells can replenish other cells within the body as long as the person or animal is alive. When a stem cell divides, it has the potential of becoming another stem cell or some specialized cell with a specific function such as a red blood cell or insulin-producing cell within the pancreas.
Adult vs. Embryonic Stem Cells
Although both adult stem cells and embryonic stem cells are similar in the way they function and behave, they are very different in terms of versatility. Since adult stem cells are located within a specific tissue or organ, they can only become specialized cells relative to that specific tissue or organ. This limits the number of possible functions such adult stem cells have when used for medicinal applications. For example, adult stem cells found within the skin can only become specialized cells used for skin cell repair. They cannot become differentiated for use as, for instance, cardiac muscle cells within the heart, or any other organ or tissue besides the skin. Adult stem cells are found in small numbers and are very rare in mature tissues. In addition, culturing adult stem cells in the laboratory environment has not been fully accomplished.
Embryonic stem cells are the choice of scientists because they are easily cultivated, readily available, and, most importantly, they are universal in application, or pluripotent. Embryonic stem cells are unique, specialized cells that can be cultured to become any specific cell type in the human body. A scientist can culture a group of embryonic stem cells into any specific type of cell he chooses, whereas adult stem cells can only become cells of the specific tissue they originated from. This makes them extremely versatile compared to adult stem cells in scientific research.
The Future of Stem Cell Research
It has been seven years since the first human embryonic stem cells were isolated for in vitro fertilization. Once scientists were able to obtain donated samples, the door was opened for a plethora of advancements in the scientific and medical worlds. Stem cell research is advancing knowledge about how an organism develops from a single cell and how healthy cells replace damaged cells within the body. Research continues to create methods that can lead to the creation of regenerative medical practices such as cell-based therapies to treat disease and cancer. There are important, essential properties of stem cells that scientists will push to discover in the coming years including determining precisely how stem cells remain unspecialized and self renewing for such extended periods of time, and identifying the signals and stimuli that cause stem cells to become differentiated. As scientists continue to expand the knowledge about stem cells, it may become possible to use the cells not only for cell-based therapies, but for screening new drugs and toxins and understanding birth defects. One thing is certain, stem cell research will take medicine and scientist to a new level with the possibility of saving countless lives in the years to follow.
I used Endnote.
Sources:
Wisconsin-Madison, (2004). "Embryonic Stem Cells". http://www.news.wisc.edu/packages/stemcells/
Schwarz, Karyn, (2004). "Stem Cell Basics". http://www.pbs.org/newshour/science/stem-cells/cellbasics.html
NIH, (2005). "Stem Cell Information". http://stemcells.nih.gov/info/basics
NPR, (2005). "Stem Cell Research". http://www.npr.org/programs/specials/stemcells/science.html
White, Deborah, (2005). "Pros & Cons of Embryonic Stem Cell Research". http://usliberals.about.com/od/stemcellresearch/i/StemCell1.htm
Lemischka, R. Ihor, (2005). "Stem Cell Biology: A View toward the Future". http://www.annalsnyas.org/cgi/content/full/1044/1/132
Shaw, Jonathan, (2004). "Stem Cell Science". http://www.harvardmagazine.com/on-line/070483.html