Stem+Cells



**"Hi! I'm Sammy! Allow me to tell you a little about myself and my friends! Just like you, all my friends are different!"**

Stem cells, like Sammy and his friends, are undifferentiated cells - they're purpose is not yet determined. However, they have the potential to become a range of different cells in the body, but are waiting for a signal from the body to begin differentiating into respective destined cell types. Until this time, they must sit patiently and divide slowly into more stem cells, identical to the stem cell they originated from. You may have notice that Sammy and his friends look exactly alike, __so what does Sammy mean when he says that all his friends are different?!__

> [|three germ layers]; endoderm (respiratory and digestive tract, etc.), mesoderm (skeletal, urogenital, and cardiovascular systems, blood & lymph cells, etc.), and ectoderm (epidermis, central nervous system, mammary glands, etc.). > [The placenta will form out of the blastocyst's outer layer of cells (trophoblast cells), so trophoblast cells will differentiate into extra-embryonic cells.] > >  Furthermore, there are specifically two characteristics that Sammy and his friends possess that define them as stem cells:
 * To solve this conundrum, we arrive at the five different types of stem cells that exist:**
 * 1)  **Early Embryonic Stem Cells:** when an ovum and sperm fuse together, they form a zygote (a newly fertilised egg). When the zygote begins to divide it forms a collection of cells called an embryo. The embryo consists of identical early embryonic stem cells.
 * 2) ** Blastocyst Embryonic Stem Cells: ** several days after the formation of the zygote, the embryo forms a hollow, spherical structure called a blastocyst. You may have already guessed that the blastocyst embryonic stem cells are contained within the blastocyst structure forming the inner cell mass. These stem cells will ultimately be a part of the foetus (unborn child) so they will differentiate into embryonic cell types (specialised cells) of the
 * 1) ** Fetal Stem Cells: ** There are two types of Fetal Stem Cells: (a) Pluripotent stem cells, which are the most basic stem cells because they are undifferentiated. As they are found in the fetus itself, they pose a few moral issues; (b) Hematopoietic stem cells are embryonic multipotent stem cell which are found in cord blood. They are already in the process of becoming blood stem cells and are therefore a form specialised/specific cell for stem cell research and use. Current treatments utilise hematopoietic stem cells in diseases of the blood, however research shows the potential for these specific cells to change into building blocks of organ tissue.
 * 2)  **Adult Stem Cells:** stem cells which are undifferentiated located in already differentiated cells in a tissue or organ after embryonic development ie. not only in full grown adults! They differentiate into the major specialized cell types of the tissue or organ in which they are found, therefore its primary use is to maintain and repair the tissue in which it is located.
 * 3) ** Oocyte Stem Cells: ** unfertilized eggs are chemically stimulated to produce a group of cells which make up a non-viable egg. This new line of stem cells exhibit the same characteristics as embryonic stem cells but are simpler cells as they only have one parent. See Stem Cell Cases for more information on this new type of cell and its uses.

>  > > > > >  > > > > > > > > ** IMPORTANT **: **PROGENITOR CELLS** are not to be confused with stem cells, though they are sometimes equated. They are in transition stage between an undifferentiated stage and a specialised stage, thus far more specific as a result of being lineage restricted. While they may exhibit potency, bring descibed as unipotent or multipotent, they do not possess the characteristic of self-renewal, distinguishing them from stem cells. Their primary role is to replace damaged tissue ie. for repair and growth. > For more information pay a visit to http://en.wikipedia.org/wiki/Progenitor_cell. >  > Content from: http://en.wikipedia.org/wiki/Stem_cells
 * 1) Self-Renewal: hold the ability to pass through numerous cycles of cell division (Mitosis) while maintaining the undifferentiated state.
 * 1) <span style="font-family: 'Comic Sans MS',cursive;">**Potency:** hold potential to differentiate into a specialised cell type from the undifferentiated state
 * <span style="font-family: 'Comic Sans MS',cursive;">This second characteristic is also what Sammy is referring to as being different. This is because there are four different types of potency a Stem Cell can possess:
 * <span style="font-family: 'Comic Sans MS',cursive;">**Totipotent/Omnipotent:** composition of the embryo in the early stages of fertilisation (zygote stage) with the potential to differentiate into embryonic and extra-embryonic cell types. They construct a complete viable organism if allowed to progress to until the end of the mother's pregnancy
 * <span style="font-family: 'Comic Sans MS',cursive;">**Pluripotent:** derived from the internal cell mass of a blastocyst (embryo; 4-5 days after fertilisation) with the potential to differentiate into nearly all specialised cells of the [|three germ layers] eg. <span style="font-family: 'Comic Sans MS',cursive;">Blastocyst Embryonic Stem Cells
 * <span style="font-family: 'Comic Sans MS',cursive;"> <span style="font-family: 'Comic Sans MS',cursive;">**Multipotent:** potential to differentiate into a member of a closely related family of cells ie. lineage restricted e.g. haematopoetic stem cells differentiate into lymphocytes, erythrocytes etc.
 * <span style="font-family: 'Comic Sans MS',cursive;">**Oligopotent:** potential to develop into a few specialised cells i.e. lymphoid or myeloid stem cells.
 * <span style="font-family: 'Comic Sans MS',cursive;">**Unipotent**: limitation of the potential to differentiate ie. can only differentiate one type of cell eg. skin cells