Stem Cells

(HowStuffWorks, 1998)
Danielle Wark
Mrs.Toope
SBI 3U1
Friday, May 17, 2014

Stem Cells

Are you looking to change the medical World as we know it but something is holding you back? Then you are a lot like stem cells. Our bodies contain many specialized cells that carry out many specialized functions, these cells are called differentiated cells. In contrast to this, a stem cell is undifferentiated where it’s role in our body is not yet determined. Stem cells are undifferentiated or unspecialized cells found in human and nonhuman animals that have the ability to continue dividing indefinitely and to differentiate into many different cell types, including more stem cells. (Aldridge, 2012) Commonly, stem cells come from two main sources: embryos formed during the blastocyst phase of embryological development called embryonic cells, and adult tissues called adult stem cells. Stem cells play an important role in our body from embryonic development through adulthood.(Crosta, 2008) This essay will answer questions like what are embryonic stem cells? What are adult stem cells? How does the stem cell develop? What are the ethical issues holding the stem cell research back? And finally, what does the future of stem cells hold for us?

(Edinburgh, 2010)
Development of the Stem Cell
Development begins when the egg and sperm meet. This event produces a special kind of stem cell that has the potential to grow into a new human being, as well as the placenta, which will nourish the embryo as it grows. (Utah, 2014) For the first few divisions all the cells remain undifferentiated; each one has the same potential as the fertilized egg. As development continues, a series of signals or instructions gradually limit each cell’s potential. (Utah, 2014) Differentiating has begun. One week after fertilization, the embryo, now called the blastocyst, looks like a lopsided hollow ball. The blastocyst consists of an inner cell mass (embryoblast) and an outer cell mass (trophoblast). (Crosta, 2008) 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. (Crosta, 2008) About 2 weeks after fertilization, the cells of the embryo organize into three layers. Cell signals restrict the potential of these cells even further; each layer will give rise to a different set of cell types. A few weeks later, the cells of the outer layer have become skin, the nervous system and the parts of the face and neck. The middle layer has become muscle, blood, blood vessels, and the beginnings of bones and connective tissue.The inner layer has now begun to form the digestive and respiratory tracts and the glands that feed into them, including the pancreas and the liver. (Utah, 2014) As development continues, cells differentiate to form the 250 or so cell types of the body. But even after birth and into adulthood, pockets of stem cells remain. These somatic (adult) stem cells play an important role in growth as well as maintenance and repair. (Utah, 2014) Some stem cells sit quietly, waiting for a signal to tell them to divide; others are constantly at work, replacing cells that are lost through daily wear and tear. As we grow from fertilized eggs into fully formed human beings, stem cells give rise to all of our differentiated tissues and organs. Stem cells continue to play an important role throughout our lives as they help to heal and maintain our bodies. (Utah, 2014)

Three layers of blastocyst.
(Edinburgh, 2010)
Embryonic Stem Cells Perhaps the best known stem cell is the embryonic stem cell which are found in the early embryo of mammals. Embryonic stem cells are pluripotent, meaning that they can give rise to all cell types of the body. (Aldridge, 2012) As the name suggests, embryonic cells are generated by transferring cells from an embryo that is in the blastocyst phase of development, (which in humans generally forms