The in vitro fertilization (IVF) technique could potentially also be used to produce blastocysts specifically for research purposes. This would facilitate the isolation of stem cells with specific genetic traits necessary for the study of particular disease. For example, it may be possible to study the origins of an inherited disease like cytic fibrosis using stem cells made from egg and sperm donors who have this disease. The creation of stem cells specifically for research using IVF is, however, ethically problematic for some people because it involves intentionally creating a blastocyst that will never develop into a human being.
Sources of Embryonic Stem Cells
In Vitro Fertilization:
The largest potential source of blastocysts for stem cell research is from in vitro fertilization (IVF) clinics. The process of IVF requires the retrieval of a woman’s eggs via a surgical procedure after undergoing an intensive regimen of “fertility drugs,” which stimulate her ovaries to produce multiple mature eggs. When IVF is used for reproductive purposes, doctors typically fertilize all of the donated eggs in order to maximize their chance of producing a viable blastocyst that can be implanted in the womb. Because not all the fertilized eggs are implanted, this has resulted in a large bank of “excess” blastocysts that are currently stored in freezers around the country. The blastocysts stored in IVF clinics could prove to be a major source of embryonic stem cells for use in medical research. However, because most of these blastocysts were created before the advent of stem cell research, most donors were not asked for their permission to use these left-over blastocysts for research.
Some find embryonic stem cell research to be morally objectionable, because when scientists remove the inner cell mass, the blastocyst no longer has the potential to become a fully developed human being.
Scientists can induce embryonic stem cells to replicate themselves in an undifferentiated state for very long periods of time before stimulating them to create specialized cells. This means that just a few embryonic stem cells can build a large bank of stem cells to be used in experiments. However, such undifferentiated stem cells could not be used directly for tissue transplants because they can cause a type of tumor called a teratoma. To be used for therapies, embryonic stem cells would first need to be differentiated into specialized cell types.
When the blastocyst is used for stem cell research, scientists remove the inner cell mass and place these cells in a culture dish with a nutrient-rich liquid where they give rise to embryonic stem cells. Embryonic stem cells seem to be more flexible than stem cells found in adults, because they have the potential to produce every cell type in the human body. They are also generally easier to collect, purify and maintain in the laboratory than adult stem cells.
In normal development, the blastocyst would implant in the wall of the uterus to become embryo and continue developing into a mature organism. Its outer cells would begin to differentiate into the progressively more specialized cell types of the body.
Embryonic stem cells
A blastocyst (BLAST-oh-sist), is a pre-implantation embryo that develops 5 days after the fertilization of an egg by a sperm. It contains all the material necessary for the development of a complete human being. The blastocyst is a mostly hollow sphere of cells that is smaller that the period at the end of this sentence. In its interior is the inner cell mass, which is composed of 30-34 cells that are referred to by scientists as a pluripotent because they can differentiate into all of the cell types of the body. In common usage, “embryo” can refer to all stages of development from fertilization until a somewhat ill-defined stage when it is called a fetus. Scientists use terms such as “morula” and “blastocyst” to refer ti precise, specific stages of pre-implantation development. In order to be as precise as possible.