What are stem cells?
Stem cells have the remarkable potential to develop into many different cell
types in the body during early life and growth. In addition, in many tissues
they serve as a sort of internal repair system,
essentially without limit to replenish other cells as
long as the
person or animal is still alive. When a stem cell
new cell has the potential either to remain a stem cell
another type of cell with a more specialized
as a muscle cell, a red blood cell, or a brain cell.
Stem cells are distinguished from other cell types
important characteristics. First, they are
unspecialized cells capable of renewing
themselves through cell division,
sometimes after long periods of inactivity.
Second, under certain physiologic or
experimental conditions, they can be
induced to become tissue- or organ-specific cells with
special functions. In some organs, such as the gut and bone marrow, stem
cells regularly divide to repair and replace worn out or damaged tissues. In
other organs, however, such as the pancreas and the heart, stem cells only
divide under special conditions.
Types of stem cells
1. Adult Stem Cells
Many adult tissues contain stem cells that can replace cells that die or
restore tissue after injury. Skin, muscle, intestine and bone marrow, for
example, each contain their own stem cells. In the bone marrow, billions of
new blood cells are made every day from blood-forming stem cells. Adult
stem cells are tissue-specific, meaning they are found in a given tissue in our
bodies and generate the mature cell types within that particular tissue or
organ. It is not clear whether all organs, such as the heart, contain stem
2. Fetal Stem Cells
As their name suggests, fetal stem cells are taken from the fetus. The
developing baby is referred to as a fetus from approximately 10 weeks of
gestation. Most tissues in a fetus contain stem cells that drive the rapid
growth and development of the organs. Like adult stem cells, fetal stem cells
are generally tissue-specific, and generate the mature cell types within the
particular tissue or organ in which they are found.
3. Umbilical Cord Blood Stem Cells
At birth the blood in the umbilical cord is rich in blood-forming stem cells.
The applications of cord blood are similar to those of adult bone marrow and
are currently used to treat diseases and conditions of the blood or to restore
the blood system after treatment for specific cancers. Like the stem cells in
adult bone marrow, cord blood stem cells are tissue-specific.
4. Embryonic Stem Cells
Embryonic stem cells are derived from very early embryos and can in theory
give rise to all cell types in the body. However, coaxing these cells to become
a particular cell type in the laboratory is not trivial. Furthermore, embryonic
stem cells carry the risk of transforming into cancerous tissue after
transplantation. To be used in cell transplant treatments the cells will most
likely need to be directed into a more mature cell type, both to be
therapeutically effective and to minimize risk that cancers develop. While
these cells are already helping us better understand diseases and hold
enormous promise for future therapies, there are currently no treatments
using embryonic stem cells accepted by the medical community.
Potency of stem cells:
• Totipotent stem cells: can differentiate into embryonic and extra
embryonic cell types. Such cells can construct a complete, viable organism.
These cells are produced from the fusion of an egg and sperm cell. The only
totipotent cells are the fertilized egg and the cells produced by the first few
divisions of the fertilized egg are also totipotent. Totipotent stem cells give
rise to somatic stem/progenitor cells and primitive germ- line stem cells.
• Pluripotent stem cells: are the descendants of totipotent cells and
can differentiate into nearly all cells, i.e. cells derived from any of the three
germ layers. These pluripotent cells are characterized by self-renewal and a
differentiation potential for all cell types of the adult organism. These are
true stem cells, with the potential to make any differentiated cell in the
body. Embryonic Stem Cells come under this category. Human pluripotent
stem cells would be invaluable for in vitro studies of aspects of human
• Multipotent stem cells: can differentiate into a number of cells, but
only those of a closely related family of cells. These are true stem cells but
can only differentiate into a limited number of types. For example, the bone
marrow contains multipotent stem cells that give rise to all the cells of the
blood but not to other types of cells. Adult Hematopoietic Stem Cells are
multipotent. Adipose tissue is a source of multipotent stem cells.
Multipotent stem cells form multiple blood cell lineages.
• Oligopotent stem cells: can differentiate into only a few cells, such
as lymphoid or myeloid stem cells. The corneal epithelium is a squamous
epithelium that is constantly renewing and is Oligopotent.
• Unipotent stem cells: can produce only one cell type, their own, but
have the property of self-renewal, which distinguishes them from non-stem
cells. Such Unipotent cells include muscle stem cells. Most epithelial tissues
self-renew throughout adult life due to the presence of unipotent progenitor
USES OF STEM CELLS
Alternate to organ transplants, example rebuilding of
bones and cartilage
Increases understanding of many diseases
such as cardiovascular diseases
Test new drugs for effectiveness and safety
Regenerative medicine to repair damaged
tissues, for example people suffering from
Parkinson’s disease, burns and strokes etc.
It is wrong, or even dangerous, to claim that human dignity and a right to life attach only
to those human organisms who fulfill specific criteria, said by the opponents of embryonic
stem cell research
Embryos can be treated in the same way as we treat any other bit of tissue as it just a
‘clump of cells’ it have no sensations or emotions it cannot survive by itself, said by the
proponents of embryonic stem cell research
The standard position of both traditional and contemporary
embryology, which is that a human life begins at fertilization.
Fertilization is the clearest moment of discontinuity in life: it is when a
new organism, one with a unique genetic identity, exists for the first