Stem Cells
Understandings: The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.
Stem cells are cells that are not fully differentiated but have the ability to divide and differentiate into different types of cells (e.g. one stem cell can differentiate into a blood cell, a liver cell or a kidney cell). Stem cells are necessary in embryonic development as all the cells in the adult organism stem from the embryonic stem cells (hence the name).
When an egg cell and a sperm cell fuse they form a zygote. This zygote then starts to divide to form a two celled embryo, then a 4 celled embryo, then an 8 celled embryo... and so on. Early in the early stages of the embryo the cells are stem cells because they are able to become any type of cell within the organism (therefore they are said to be totipotent stem cells --> arises from the word total) and can divide multiple times. Gradually as the embryo cells divide they start to become committed to a specific path so for example some cells become committed to being kidney cells. So even though they retain their ability to differentiate, they can only differentiate into kidney cells (and no longer liver or blood cells for example), therefore they are no longer stem cells and are said to be unipotent (uni = one). However a small amount of stem cells are still found in the adult organism, e.g. stem cells can still be found in the skin, bone marrow and liver. Even though these stem cells are not able to differentiate into all the different types of cells in the organism (unlike the embryo stem cells that are totipotent these are only pluripotent --> arises from the word plural --> many but not total) they are still able to differentiate into a range of different cells so in the case of stem cells within the bone marrow, these are not able to differentiate into liver cells for example but are able to differentiate into a multitude of white blood cells and into red blood cells. So even though these remaining stem cells are not as effective as embryonic stem cells they still greatly benefit the adult organism in terms of regeneration and repair of damaged tissue.
Since stem cells are able to differentiate multiple times and into different cell types, they are ideal for therapeutic use in degenerative diseases or tissue repair. See below.
Figure 1.1.8 - Stem Cells
Summary:
- Stem cells can divide many times and into many types of cells
- Early stage embryo is made up of stem cells --> all future cells stem from these
- As the embryonic cells divide they gradually become committed and therefore are no longer stem cells
- Some stem cells remain in the adult organism (e.g. bone marrow, skin and liver)
- These adult stem cells are pluripotent but not totipotent (i.e. can differentiate into many different cells but not all types of cells)
- Adult stem cells are vital for repair and regeneration of damaged tissue
- Stem cells are ideal for therapeutic use in tissue repair and degenerative diseases
Figure 1.1.8 - "Stem cells diagram" by Mike Jones - From English Wikipedia. Original description page is/was here.Comment: The source of pluripotent stems cells from developing embryos. Original work by Mike Jones for Wikipedia.. Licensed under Creative Commons Attribution-Share Alike 2.5 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Stem_cells_diagram.png#mediaviewer/File:Stem_cells_diagram.png
