Stem cells review

Stem cells are unspecialised cells capable of developing into many different types of cells.

Stem cells found in embryos are called embryonic stem cells and develop into all the different types of cell in the body.

Adults also contain stem cells. These are found in small numbers in many organs, including bone marrow, brain, skin and muscle.

Up until the eight cell stage, all of the cells in a human embryo are identical. At this stage, these stem cells are unspecialised and can therefore differentiate into many different types of cell.

After the eight cell stage, most of the embryonic cells become specialised and can no longer differentiate. Some will become nerve cells, others will become blood cells, muscle cells,bone cells, etc...

Adult stem cells are found in small numbers in many organs and tissues, such as bone marrow.

Adult sem cells normally maintain and repair damaged tissue, and, unlike embryonic stem cells, can usually only make a small number of cell types. For example, adult stem cells in the skin only normally form skin cells.

Research has shown that some adult stem cells can be manipulated to produce many different cell types (e.g. brain stem cells can make muscle cells). This is called plasticity.

Plants also have stem cells. Plant cells can differentiate to form specific cells throughout the plant's life. Animal cells lose this ability early in their life cycle.

Unspecialised plant cells are found in tissues called meristems. Plant stem cells can become specialised to form tissues such as:

• xylem: these cells transport water and minerals up the stem from the roots to the shoots and leaves
• phloem: these cells transport sugars, produced in the leaves, up and down the stem.

These new types of tissue can be found in the flowers, leaves, stems and roots of the plant.

Most stem cell research has used cells obtained from embryos left over from fertility treatment.

These are called embryonic stem cells and are the most powerful type because they can turn into any type of cell.

Their use in research is strongly critized by people who believe it is unethical to kill embryos for their cells.

Work involving embryonic stem cells is subject to government regulation.

Adult stem cells are not as powerful as embryonic stem cells, but they do have other advantages.

• They come from volunteers so they are more ethically acceptable
• A patients own stem cells could be used to treat their own disease, avoiding the problem of immune rejection
• It might be easier to guide their development into specific cell types
• hey are less likely to become cancerous

There is a great deal of research into using adult stem cells to treat diseases. They could reduce the need for organ transplants, which have long waiting lists.

Studying adult stem cells and how they differentiate into different cell types could also provide useful information on how cancers arise and develop, and could therefore lead to improved cancer treatments.

bone marrow – The spongy tissue in the centre of bones that is a rich source of adult stem cells

differentiation – The process by which a cell specializes into a specific type

embryo – The early stage of animal development, when it is just a cluster of cells

embryonic stem cells – Stem cells that are found in embryos and can develop into all the different types of cell in the body

meristem – An undifferentiated region of a plant in which cells divide

phloem – Plant tissue that transports food

stem cell – An unspecialized cell that can potentially become any type of cell

xylem – Plant tissue that transports water and minerals

totipotent - capable of becoming any type of cell