WASHINGTON, March 9 (Xinhua) -- U.S. President Barack Obama on Monday issued an executive order that allows federal money to fund expanded embryonic stem cell research. The following are answers to some common questions about stem cells:
-- What are stem cells?
Stem cells are master cells that have the ability to transform themselves into other cell types, including those in the brain, heart, bones, muscles and skin.
-- What are embryonic stem cells?
Embryonic stem cells are cells contained in embryos that have the ability to transform themselves into virtually any other type of cell in the body. They are called pluripotent. It is this quality that enables the tiny embryo to develop into a fully formed body. About five days after fertilization, the human embryo becomes a blastocyst -- a hollow sphere of about 100 cells. Cells in its outer layer go on to form the placenta and other organs needed to support fetal development in the uterus. The inner cells go on to form nearly all of the tissues of the body. These are the embryonic stem cells used in research.
-- What are adult stem cells?
The name is a misnomer because they are harbored in mature tissue -- in the bodies of children as well as adults. Adult stem cells are more specialized than embryonic ones and give rise to specific cell types. They are called multipotent. The mature body uses these cells as "spare parts" to replace other worn out cells. For example, certain stem cells in the bone marrow spawn red blood cells, white blood cells and blood platelets. Recent research has suggested adult stem cells can turn into many more cell types than once believed possible.
-- What is the source of embryonic stem cells?
Scientists generally harvest embryonic stem cells from embryosleft over in fertility clinics after in vitrofertilization techniques. These "test-tube baby" techniques, used to help infertile couples have a baby, involve fertilizing a woman's egg cells with a man's sperm cells in a laboratory dish. Several embryos are created at a time, and not all are implanted into the mother's womb to create live births. Embryos left over by the couple are slated for destruction by the fertility clinic. These can serve as the source for deriving stem cells, a process that involves removing the blastocyst's inner cells and destroying the embryo.
-- What are the possible medical uses for stem cells?
Scientists hope to harness the transformational qualities of stem cells to provide treatments for a variety of diseases affecting millions of people worldwide. Because stem cells can turn into many other cell types with the right prompting, doctors may be able to replace tissues and organs damaged by disease or injury to restore healthy function. For example, in people with Parkinson's disease, injecting stem cells into the area of the brain that controls muscle movement, where the disease kills nerve cells, might regenerate the neurons and reverse the illnesses. This procedure would be called a stem cell transplantation. Therapeutic applications of stem cells potentially also could treat illnesses including: diabetes, Alzheimer's disease, stroke, heart attack, multiple sclerosis, blood, bone and bone marrow ailments, severe burns by providing skin grafts, spinal cord injuries, and cancer patients who have lost cells and tissue to radiation and chemotherapy.
-- What other medical uses are possible?
Using stem cells, researchers would be able to test a drug's therapeutic effects and toxic side effects in human tissue without using a laboratory animal as a proxy. Sometimes the reaction of laboratory animals to a given drug does not match the human reaction to the drug. In addition, stem cells could be harnessed and packaged to deliver gene therapies to specific targets in the body to treat genetic problems.
-- What's the controversy?
For some people, the destruction of any embryo is tantamount to murdering a human being. Some religious and political figures hold this view.