What are stem cells?
Stem cells are the master cells of the human body. They can divide to produce copies of themselves and many other types of cell. They are found in various parts of the human body at every stage of development from embryo to adult. Stem cells taken from embryos that are just a few days old, can turn into any of the 300 different types of cell that make up the adult body.
What types of stem cell exist?
Stem cells can be classified into three broad categories, based on their ability to differentiate. Totipotent stem cells are found only in early embryos. Each cell can form a complete organism (e.g.) identical twins. Pluripotent stem cells exist in the undifferentiated inner cell mass of the blastocyst and can form any of the 200 different cell types found in the body. Multipotent stem cells are derived from foetal tissue, cord blood and adult stem cells. Although their ability to differentiate is more limited than pluripotent stem cells, they already have a track record of success in cell-based therapies. Here is a current list of the sources of stem cells:
Embryonic stem cell. Are harvested from the inner cell mass of the blastocyst seven to ten days after fertilisation.
Foetal stem cells are taken from the germline tissues that will make up the gonads of aborted foetuses.
Umbilical cord stem cells- umbilical cord blood contains stem cells similar to those found in bone marrow which are use to treat haematopoietic disorders.
Placenta derived stem cells. Up to ten times as many stem cells can be harvested from a placenta as from cord blood
Adult stem cells. Many adult tissues contain stem cells that can be isolated mainly from bone marrow.

Why stem cells are important?
Stem cells have two important characteristics that distinguish them from other types of cells. First, they are unspecialised cells that renew themselves for long periods through cell division. The second is that under certain physiological or experimental conditions, they can be induced to become cells with special functions such as the beating cells of the heart muscle or the insulin-producing cells of the pancreas.

Ethics
This article tries to shed some light on how stem cells may be able to cure diabetes in the future and why their use is controversial. It aims merely to inform and elucidate some of the controversies surrounding this area of research.
Stem cells are the basis for every type of cell in the body; they possess the ability to develop into any of the body's tissues. The National Bioethics Advisory Commission, Ethical Issues in Human Stem Cell Research, 1999 states:
"Many kinds of stem cells are found in the body, with some more differentiated, or committed to a particular function than others. In other words when stem cells divide, some of the progeny mature into cells of a specific type (eg. Heart, muscle, blood or brain cells), while others remain stem cells, ready to repair some of the everyday wear and tear undergone by our bodies. These stem cells are capable of continually reproducing themselves and serve to renew tissues throughout an individual's life. .... Although the term stem cell commonly is used to refer to the cells within the adult organism that renew tissue, the most fundamental and extraordinary type of stem cell are found in the early stage embryo. These embryonic stem (ES) cells, unlike the more differentiated adult stem cells or other cell types, retain their totipotency."
Scientists are hoping to discover how to turn these stem cells into specific cells to replace ones that are damaged .i.e. to turn stem cells into insulin-producing cells. As well as potentially curing diabetes, it is hoped that this technique could also treat sufferers of Parkinson’s disease, Alzheimer's and spinal chord injury.
The ethical challenges arise in acquiring the cells for research. The only way to harvest the cells is by destroying the embryo. This raises important moral issues in relation to the