Biomedical Engineering Reference
In-Depth Information
been definitively proven in bone marrow, brain tissue, the gut, the
liver, skin, teeth, peripheral blood, blood tissues, skeletal muscle,
some ovarian tissues and the testes (NIH, 2010). Adult stem cells are
effectively pre-cursor cells that can give rise to a number of different
cell types. For example, one type of adult stem cell found in bone
marrow - haematopoietic stem cells - can produce all of the different
blood cells found in the body. This amounts to some nine different
cell types, all from one 'pre-cursor' cell. Adult stem cells are thought
to be stored in special 'stem cell niches' in the organs and tissues in
which they are found, ready to be called upon when needed for cell
repair or activated by disease or damage.
Experimental work remains to determine exactly how adult stem
cells develop, how they remain in their undifferentiated state when
the other tissues have differentiated, what it is about the 'stem cell
niches' that causes them to stay where they are until needed, what
tissues they can be found in and how differentiation might be
triggered and controlled (NIH, 2010). Various properties of adult
stem cells have also been observed that require further study, such as
their capacity to differentiate into cells that are not known to be of
the lineage they generally lead to, and the capacity for adult stem
cells to be genetically engineered so that they show the same
properties as human embryonic stem cells (NIH, 2010).
In contrast to the embryonic stem cells that need to be extracted
from a very early-stage embryo before it begins to differentiate into
the various structures that make up the human or animal body, adult
stem cells are sourced after differentiation has begun. In theory, adult
stem cells therefore avoid the ethical issues involved in using human
embryos. They are also thought to be easier to direct into specific cell
types because they are already at least partially differentiated, even
though there is still a lot that remains unknown about exactly how to
control differentiation. The other main advantage of adult stem cells
over embryonic stem cells is that because they come from an already
developed individual, they are supposed to be, in essence, already
tailor-made for the same individual.
The adult stem cell types that have been identified - haematopoietic,
neuronal, mesenchymal, epithelial and epidermal - have also been
