| An adult human being is made up of
many different types of very specialised cells organised into tissues
and organs which carry out particular jobs within our bodies – muscle
cells contract, nerve cells carry electrical messages, liver cells
deal with toxic waste etc etc. so it seems a bit of a contradiction
to talk about adult stem cells, when we have seen that stem cells
are simple undifferentiated cells. However they do exist –
adult stem cells are undifferentiated cells which are found among
the normal differentiated cells in a tissue or organ of the body.
They can differentiate when needed to produce any one of the major
cell types found in that particular tissue or organ. Another term
for adult stem cells is somatic stem cells. No-one is quite
sure where they originate from, but they are definitely there!
We have known about the stem cells in bone marrow which are capable
of forming blood cells for about thirty years, and bone marrow transplants
are used regularly in the treatment of certain cancers and immune
system diseases. Gradually over the years scientists have discovered
stem cells in the bone marrow which can generate bone, fat, cartilage
and fibrous tissue and in the 1990s stem cells in the brain which
can form the three main types of brain cells. In fact adult stem
cells have been found in many different organs and tissues. The
problem with them is that there are only a very small number of
stem cells in each different tissue. They are very difficult to
extract and most of them form a very limited range of differentiated
cells – they are said to be multipotent.
What is more they are extremely difficult to grow in the laboratory.
Scientists are working hard to develop better ways of culturing
these adult stem cells because large numbers of cells are
needed for stem cell therapy. They also need to find the triggers
which persuade the stem cells to differentiate into specific
cells types. If these problems can be cracked, adult stem
cells could offer hope for people with diseases ranging from
Parkinson’s disease affecting the brain to the muscle
destruction seen after a heart attack. Because stem cells
could be harvested from the individual who needs them, a rejection-free
treatment could be available in the future. |
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