What is the source of embryonic stem cells?
Embryonic stem cells, as their name suggests, are derived from embryos. Specifically, embryonic stem cells are derived from embryos that develop from eggs that have been fertilized in a dish in an in vitro fertilization clinic — and then donated for research purposes with informed consent of the donors. They are not derived from eggs fertilized in a woman’s body. The embryos from which human embryonic stem cells are derived are typically four to five days old and are a hollow microscopic ball of cells called the blastocyst. Each blastocyst consists of 50 to 150 cells and includes three structures: an outer layer of cells that form the placenta, a fluid-filled cavity, and a group of about 30 pluripotent cells at one end of the cavity. This latter group of cells, called the inner cell mass, forms all the cells of the body [Source: National Institutes of Health].
