1. Stem cells
Chapter 7
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2. What are stem cells?
They are undifferentiated cells that have the potential to replicate and to develop into many different types of body cells.

3. Potency of stem cells
Different kinds of stem cells can be distinguished in terms of their potency to produce different cell types. Descriptions of stem cell potencies include:
Totipotent (meaning total potential)
This has the potential to create any type of cell
Fertilised egg
Pluripotent
These come from the inner cell mass of the blastocyst.
These are able to give rise to all cell types in a foetus i.e. adult cells
Multipotent
These have the ability to differentiate into a closely related family member e.g. a multipotent blood cell can give rise to red blood cells, white blood cells and platelets. Likewise a multipotent skin cell can give rise to all types of skin cells.
These exist in both adult cells and embryos. The best understood is the blood stem cell.

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5. Types of stem cells There are two main types of stem cells
Embryonic stem cells
Adult stem cells (more accurately called somatic stem cells)

6. Embryonic Stem Cells
Embryonic stem cells are obtained from the inner cell mass of a blastocyst (3-5 day old embryo)
A single cell is isolated from the inner cell mass and grown in culture, dividing by mitosis to produce a culture of stem cells.
The Embryonic Stem Cells are obtained from extra embryos created as part of the IVF procedures and are in excess of requirements.
Taking these cells from the inner mass of a blastocyst destroys an embryo and this procedure has raised ethical issues.
Embryonic stem cells are pluripotent, meaning they can give rise to any type of cell in the fully developed body. (Embryonic stem cells can’t create the placenta or umbilical cord tissues, but they appear to be able to generate any other type of cell.)
In other words – they have never been implanted into a womens uterus and will be discarded if not used for research

8. Adult somatic stem cells
So far, scientists have verified stem cell niches in several tissues, including bone marrow, the brain, fatty tissue (called adipose tissue), the liver and blood. Another source of stem cells is umbilical cord blood which can be harvested after birth.
Adult stem cells are generally multipotent, able to give rise to several kinds of cells in their home tissues.
In their normal environments, adult stem cells don’t seem to generate cell types outside their particular tissues. E.g. liver stem cells, for example, don’t generate heart cells, and brain stem cells don’t generate kidney cells.

11. Induced Pluripotent Stem Cells (iPS cells)
Discovered in 2006 by Shinya Yamamaka in Japan who went on to be the co-recipient of the Nobel Prize for Physiology and Medicine in 2012.
Stem cell researchers have developed a technique for reprogramming adult cells in the lab to get them to act more like embryonic stem cells.
These reprogrammed cells are called induced pluripotent stem cells (iPS cells), and they can be made from adult cells in the skin, fatty tissue, and other sources.
The ability to produce iPS cells means that unhealthy cells such as skin cells from a person suffering Parkinson’s Disease, can be studied in detail in cell cultures in the laboratory, allowing the effectiveness of new drugs to be explored.
Cell-based therapies using iPS cells are not practical just yet. The current procedure for reprogramming somatic cells involves genetic modification which can sometimes cause cells to produce tumours.

12. Stem Cell Research
Stem cells have three characteristics that distinguish them from other cells
They have not yet gone through differentiation
They are capable of repeated division by mitosis for long periods of time
Given the right conditions they can differentiate into specialised cells.
Because they are able to differentiate into cells of many different types, they are involved in intense scientific research. It is hoped that they will be able to use stem cells in stem cell based therapies to treat diseases.
If this is able to occur stem cells may be able to be differentiated into particular tissues for treating conditions such as stroke, spinal cord injury, burns, heart disease, diabetes, arthritis, Alzheimer’s disease and Parkinson’s disease.
May also help with greater research into toxins and their effect on the body and for understanding causes of birth defects