Stem cells are self-renewing, unspecialized cells that can give rise to all of the 210 specialized cells in the body. Differentiation is the process by which stem cells divide and form specialized cells that can perform special functions, such as blood stem cell formation or nerve cell transmission.
Stem cells may be totipotent, pluripotent, or multipotent. The fertilized egg or zygote and the first division into the two-cell blastomeres are totipotent, meaning that its potential is total, each capable of developing into a human being. In fact, identical twins develop when the zygote or blastomere separate and develop into two individual, genetically identical human beings.
A few days after fertilization, a hollow sphere called a blastocyst is formed, the outer cells of which are called the trophoblast and form the placenta, and the inner cluster of cells are called the inner cell mass. The inner cell mass are known as the pluripotent stem cells, and these form the embryo. While they can form all 210 types of cells of the human body, they are unable to form a human being, because they lack the trophoblast which attaches to the uterus and forms the placenta.
The pluripotent stem cells undergo further specialization into stem cells that are committed to give rise to cells that have a particular function, such as nerve stem cells, or blood stem cells which produce red blood cells, white blood cells, and platelets. These more specialized stem cells are called multipotent. Adult stem cells have been identified in many organs and tissues, including bone marrow, peripheral blood, blood vessels, skeletal muscle, skin and teeth, brain and heart. Bone marrow contains at least two kinds of stem cells: hematopoietic stem cells, which form all types of blood cells in the body, and mesenchymal stem cells, which form supporting tissue for bone marrow, such as bone, fat, and cartilage.
An allogeneic stem cell transplant, where a donor who is genetically similar to the patient such as a brother or sister, is now employed to treat refractory cancers such as chronic lymphocytic leukemia unresponsive to standard chemotherapy. Adult Hematopoietic stem cells and Mesenchymal stem cells from umbilical cord blood are promising new areas of stem cell research.
The ethical concern in Stem Cell Research is the source of stem-cells. The use of stem-cells from newborn placental or umbilical cord blood or adult bone-marrows without loss of natural life is ethical.
The moral viewpoint is opposed to the creation of embryos by in-vitro fertilization or somatic cell nuclear transfer and then harvesting stem cells and destroying the lives of the most vulnerable human beings for the benefit of those already living. To command the death of others so that one's own life may be enhanced or prolonged is completely opposed to human rights. In effect, it is a form of cannibalism - killing a human being for the survival of another.
In the New Testament, Jesus Christ himself said: "If you wish to enter into life, keep the commandments." When asked which ones, he referred to the Law of Moses (Exodus 20), "Thou shalt not kill" (Gospel of Matthew 19:17-18).
As Pope John Paul II expressed in The Splendor of Truth, "it is never lawful, even for the gravest reasons, to do evil that good may come of it (Romans 3:8) — in other words, to intend directly something which of its very nature contradicts the moral order, and which must therefore be judged unworthy of man."
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