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* DISCLAIMER - The following is not medical advice, only the *
* personal opinion of the writer. Any contemplated change in *
* treatment or medication must be referred to your treating  *
* medical practitioner. Dr. J. F. Slattery PhD Soc           * 
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I think it might be helpful when discussing stem cell research, if all 
concerned were
aware of the meaning of the various terms used. For example, many on one 
side confuse
the term "embryo" with the term "foetus". The following may help.
Dr James F Slattery, PhD Soc Sci
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STEM CELL RESEARCH
OVUM - a human female sex cell, an egg.
SPERMATOZOON - a human male sex cell.
ZYGOTE - cell formed by the fusion of a sperm and an ovum during 
fertilization,usually occurring in the ampulla of the fallopian tube, until 
the first division. When the zygote starts to divide and multiply, it is 
called an embryo.
BLASTOCYST - an early stage embryo consisting of no more than 100 or so 
cells.
FIBROBLAST - A fibroblast is a type of cell that synthesizes and maintains 
the extracellular matrix of many animal tissues. Fibroblasts provide a 
structural framework (stroma) for many tissues, and play a critical role in 
wound healing. They are the most common cells of connective tissue in 
animals.
EMBRYO - in humans, the developing organism from about two weeks after 
fertilization to the end of the seventh or eighth week.
POTENCY DEFINITIONS
·       Totipotent (a.k.a omnipotent) 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. Cells produced by the first few divisions of the 
fertilized egg are also totipotent.
·       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.
·       Multipotent stem cells can differentiate into a number of cells, but 
only those of a closely related family of cells.
·       Oligopotent stem cells can differentiate into only a few cells, such 
as lymphoid or myeloid stem cells.
·       Unipotent cells can produce only one cell type, their own, but have 
the property of self-renewal, which distinguishes them from non-stem cells 
(e.g. muscle stem cells).
EMBRYONIC STEM CELLS
Cells derived from the inner cell mass of an early stage embryo known as a 
blastocyst. Human embryos reach the blastocyst stage 4-5 days post 
fertilization, at which time they consist of 50-150 cells. In a developing 
embryo, stem cells can differentiate into all of the specialized embryonic 
tissues.
Embryonic stem cells are pluripotent. This means they are able to 
differentiate into all derivatives of the three primary germ layers: 
ectoderm, endoderm, and mesoderm. These include each of the more than 220 
cell types in the adult body. Pluripotency distinguishes embryonic stem 
cells from multipotent progenitor cells found in the adult; that only form a 
limited number of cell types. When given no stimuli for differentiation 
(i.e. when grown in vitro - in glass), embryonic stem cells maintain 
pluripotency through multiple cell divisions.
ADULT STEM CELLS
Undifferentiated cells, found throughout the body after embryonic 
development, which multiply by cell division to replenish dying cells and 
regenerate damaged tissues. Also known as somatic stem cells (meaning 'of 
the body'), they can be found in juvenile as well as adult animals and 
humans. The term refers to any cell that is found in a developed 
organism,which has two properties: the ability to divide and create another 
cell like itself and also divide and create a cell more differentiated than 
itself. Also known as somatic stem cells and germline (giving rise to 
gametes) stem cells, they can be found in children, as well as adults.
The presence of pluripotent adult stem cells remains a subject of scientific 
debate; however, research has demonstrated that pluripotent stem cells can 
be directly generated from adult fibroblast cultures Because of their 
plasticity and potentially unlimited capacity for self-renewal, embryonic 
stem cells therapies have been proposed for regenerative medicine and tissue 
replacement after injury or disease. However, to date, no approved medical 
treatments have been derived from embryonic stem cells research. Adult stem 
cells and cord blood stems cells have thus far been the only stem cells used 
to successfully treat any diseases.
Besides the ethical concerns of stem cell therapy, there is a technical 
problem of graft-versus-host disease associated with allogeneic 
(incompatible) stem cell transplantation. However, these problems may be 
solved using the recipient's own adult stem cells or via therapeutic 
cloning.
CLONING
To create a clone, a scientist removes the nucleus from a donor cell, then 
places it into an ovum (egg)  from which the nucleus has been removed. The 
scientist then "tricks" the egg into thinking it's been fertilized. The egg 
develops into a blastocyst. The scientist can then remove the stem cells 
from this blastocyst or place it into a uterus where it has the potential to 
develop into a foetus.
Here's where things get complicated. The original donated nucleus may have 
come from, say, a skin cell. For a viable foetus to develop, the egg needs 
to reprogram the genome of the skin cell, shutting off genes specific for 
skin tissue and turning on genes needed for embryonic development, genes 
that are normally dormant in tissue-specific cells. In other words, the egg 
needs to erase all tissue-specific memories from the skin cell and revert it 
into a genomic blank slate.
But this entire process is almost never perfect, and nearly all cells in a 
cloned blastocyst retain some memory of their original source. As a result, 
the developing foetus inevitably has some degree of genetic abnormality. 
Most clones, in fact, die in utero or at birth. The few clones that make it 
into adulthood are often plagued by bizarre health complications. This is 
one reason why scientists generally believe that attempting to clone a human 
being is morally reprehensible.
Scientific interest in adult stem cells has centred on their ability to 
divide or self-renew indefinitely, and generate all the cell types of the 
organ from which they originate, potentially regenerating the entire organ 
from a few cells. Unlike embryonic stem cells, the use of adult stem cells 
in research and therapy is not considered to be controversial as they are 
derived from adult tissue samples rather than destroyed human embryos. They 
have mainly been studied in humans and model organisms such as mice and 
rats.
Pluripotent adult stem cells are rare and generally small in number but can 
be found in a number of tissues including umbilical cord blood. A great deal 
of adult stem cell research has focused on clarifying their capacity to 
divide or self-renew indefinitely and their differentiation potential. In 
mice, pluripotent stem cells are directly generated from adult fibroblast 
cultures. Unfortunately, many mice don't live long with stem cell organs. 
Most adult stem cells are lineage-restricted (multipotent) and are generally 
referred to by their tissue origin (mesenchymal stem cell, adipose-derived 
stem cell, endothelial stem cell, etc.)
Adult stem cell treatments have been successfully used for many years to 
treat leukaemia and related bone/blood cancers through bone marrow 
transplants. Adult stem cells are also used in veterinary medicine to treat 
tendon and ligament injuries in horses. The use of adult stem cells in 
research and therapy is not as controversial as embryonic stem cells, 
because the production of adult stem cells does not require the destruction 
of an embryo. Additionally, because in some instances adult stem cells can 
be obtained from the intended recipient, (an autograft) the risk of 
rejection is essentially non-existent in these situations. 

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