Definition: What are Stem Cells? Stem cells are undifferentiated or ‘blank’ cells found in the human body that have the potential to develop into many different cell types that carry out different functions. Most cells in the human body are differentiated. That means they are built to function in a particular organ system and carry out a specific function. A red blood cell, for example, is designed to carry oxygen, while a white blood cell is designed to fight off disease. These differentiated cells result from the process of cell division, a process that begins with undifferentiated stem cells. Pluripotent stem cells, found in embryos, can give rise to all the cells found in the human body – cells as diverse as those found in the brain, bone, heart and skin. Multipotent stem cells, found in adults or in babies' umbilical cords, have a more limited capacity. Their development is limited to the cells that make up the organ system that they originated from. For example, a multipotent stem cell in the bone marrow can develop into a red blood cell, a blood platelet or a white blood cell, but not into a skin cell or brain cell. Researchers believe that stem cells, especially pluripotent stem cells, hold much potential for medical therapies and medical research such as:
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Growing replacement cells or whole replacement organs. Human stem cells can be used to generate specialized cells in a laboratory and then be transplanted to replace damaged cells in the body. These could be used to treat a range of conditions from Parkinson disease to heart failure to spinal injuries. For example, in the case of a spinal injury, neural stem cells could be generated to replace damaged tissue. "Patching" organs that don't work properly - like helping a diabetic person's pancreas produce insulin. The newest therapies in research on stem cells and diabetes involve generating islet cells that produce insulin to replace those that a diabetic person’s immune system destroys. In the study of human development, stem cells could help researchers determine why, in the early stages of development, some cells become cancerous or how genetic diseases develop. This could lead to answers as to how they might be prevented. For research purposes, stem cells may be useful as a testing ground for new drugs before they are used on humans. Stem cells may be more accurate for research results than using animal subjects, as well as solve the ethical dilemma of using animals for medical testing.

Stem cell research has the potential to bring new treatment options to patients with Alzheimer's, Parkinson's disease, heart disease, burns, diabetes, and spinal cord injuries.

Ethical Issues Research that uses multipotent stem cells (which are found in adults and in umbilical cords) is not generally considered controversial. However, because their ability to differentiate is limited, so is their usefulness in research.

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However, research with pluripotent stem cells is controversial because it requires destroying an artificially-fertilized embryo at the 5-14 day stage. Because pluripotent stem cells can differentiate into all the cell types in the human body, they have the greatest application in research for new medical treatments. Recently, researchers at the biotech company, Advanced Cell Technology, claim to have succeeded in harvesting stem cells from mouse embryos without killing them. If this technique is valid and its reliability improved, it could alleviate many of the ethical problems related to stem cell research. Whether or not to use stem cells in research or medical therapy raises a number of ethical issues:
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When does a human embryo attain personhood? Should we use research methods that destroy human embryos to search for new therapies that could help people in the future? Where should the embryos for stem cell research come from? Will stem cell research lead to future genetic