The topic of embryonic stem cell research has been the subject of much political, religious, ethical and scientific debate. Embryonic stem cells should not be confused with stem cells obtained from the blood of adults or umbilical cord blood, which are used in stem cell transplants for patients with cancer and other life-threatening diseases.

Embryonic stem cells come from human embryos about five days after sperm fertilizes an egg. At this stage, the embryo is called a blastocyst and consists of between 50 and 150 cells, and is smaller than the period at the end of this sentence.

These embryos are created during infertility treatments or by scientists intending to use the stem cells for research. They are conceived in a laboratory, not in a woman's uterus.

For example, couples who have been unable to conceive a child may opt for infertility treatment. One option is in vitro fertilization, in which sperm from the man is mixed with eggs from the woman. In many cases, more than one embryo is created. Depending on the wishes of the couple, extra embryos that are not implanted in the woman's uterus may be frozen indefinitely, destroyed, donated to another infertile couple or donated for research.

It is estimated that 400,000 human embryos are frozen and stored at infertility clinics across the United States.

Many researchers believe that embryonic stem cells have much greater potential to treat and cure disease than do adult stem cells. The undifferentiated stem cells of a blastocyst have the potential to become brain, blood, kidney, lung, liver, heart, bone, nerve and skin cells, as well as the cells of every other tissue or organ in the body.

Adult stem cells (and stem cells from the umbilical cord of newborns) can only change into cells of one specific type, such as blood cells.

Adult stem cells have been studied since the 1960s, and the use of adult stem cell transplants for certain illnesses is well established.

Embryonic stem cell research began in 1998 when the first embryonic stem cells were isolated. Since this is a new field for researchers, no proven medical treatments have been developed yet.

The diseases and conditions researchers believe can be treated or cured with stem cells include:

• Spinal cord injuries causing paralysis

• Insulin-dependent diabetes

• Parkinson's disease

• Lou Gehrig's disease (amyotrophic lateral sclerosis)

• Muscular dystrophy

• Multiple sclerosis

• Heart failure

• Kidney failure

• Blindness

• Baldness

Scientists hope to develop methods by which embryonic stem cells can be used to create very specific types of cells, tissues or organs to treat these and other medical conditions.

Today, privately funded research institutes carry out most embryonic stem cell research in the United States. Since 2001, federal funding of embryonic stem cell research has been limited to research on already-existing stem cell lines. Other countries - Singapore, South Korea, China, Israel, Australia and the U.K. - fund embryonic stem cell research without this restriction.

Nearly everyone agrees that finding treatments for serious diseases should be a top priority for medical researchers, and that embryonic stem cell research may lead to important breakthroughs.

Opponents of embryonic stem cell research believe that using human embryos - which have the potential to develop into a fetus and to be born - is wrong because the embryos are being deprived of their capacity for life.

Proponents argue that using these embryos for research is right because of the potential to alleviate human suffering if treatments for serious diseases are developed. They also emphasize that these embryos are usually destroyed or frozen indefinitely, and are unlikely to be given the chance to develop to maturity.

Kathryn B. Brown is a family nurse practitioner with a master's degree in nursing from OHSU. Is there a health topic you would like to read about? Send ideas to You can find more local health news and information in the Health section at