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Some cells (but not all) have the ability to multiply by division. Most of the diseases known to medical science are due to malfunction of cells, to premature cell death, or to cells' wrong multiplication rates.
Stem cells are a particular kind of cells, with two major characteristics:
'''1. ''' they are unspecialized cells that can divide over and over for very long periods of time; '''2. ''' under certain conditions, they can be induced to become cells with special functions (like muscle cells, liver cells, neurons etc.)
Stem cells are naturally occurring in the human body (and other living organisms) at all levels of development. As organisms develop, stem cells become specialized types of cells. They are harder to find, and lose much of their ability to differentiate. Stem cells are the way the organism generates all the specialized cells needed for development and functioning.
There are two kinds of stem cells used in biomedical research:
'''1. ''' embryonic stem cells - which occur only in early development; '''2. ''' adult stem cells - occurring in adult organisms;
In the fetus, stem cells in developing tissue give rise to the multiple specialized cells types that make the human body. In some adult tissues, such as bone marrow, muscle and brain, discrete populations of adult stem cells generate replacement cells. While both types of stem cells are very important for biomedical research, the use of embryonic stem cells raises most of the bioethical issues.
The embryos used in stem cell research come from three major sources:
'''A. ''' In Vitro Fertilization - some of the embryos used in human stem cells research were initially created for infertility purposes through in vitro fertilization procedures. When they were no longer needed for that purpose, they were donated for research with the informed consent of the donor. '''B. ''' Somatic Cell Nuclear Transfer - embryos can be created by transferring the nucleus of a donor cell into an enucleated oocyte. The embryo will be genetically identical to the donor. '''C. ''' Embryonic germ cells are obtained from aborted fetus tissue.
The stem cells extraction procedure ends the ability of the embryo to develop through implantation in the uterus. The removal of the stem cells brings the existence of the embryo to an end.
The scientific medicine of the future will be probably based on cell therapies, focused on repair and regeneration of tissues by cell transplants. In a rough way: instead of administering lots of chemical substances in an attempt to prevent cell malfunction or premature cell death, why not just replace the cells in question? Many scientists take the view that the benefits which might flow to humanity from this form of research are so great that it is important that it be allowed to proceed.
'''''The Moral Status Of The Embryo'''''
