Embryonic Stem Cell - the basics

(Diagram from: wikipedia)

As the word embryonic implies, Embryonic Stem cells (ESC) are derived from live embryo's. You all know how embryo's are formed: a sperm cell fertilizes an egg and tadaa you get the zygote.

Zygote would start dividing into more cells in less than 30hours after fertilization, and in about 3-4 days it would have formed something referred to as the MORULA (compact mass of approximately 12 cells). And by the 5th or the 6th day, the cells would have divided into a bigger mass of cells called the BLASTOCYST (made up of an outer layer called the trophoblast made up of 70 or so cells and an inner cell mass made up of 30 or so cells).

The inner cell mass contains cells with the ability to divide and specialize into any cell except for the "extra-embryonic" cells such as the placental cells (these are made by the cells in the trophoblast), thus these cells referred as PLURIPOTENT.

The 30 or so pluripotent inner mass cells can be isolated, and grown in a petri-dish containing nutrient broth, and sub-cultured to form millions of Embryonic stem cells that can be frozen and stored for research, treatments etc.

As mentioned before, these cells posses the ability to convert into any type of cell in the body, and this conversion can be induced by simply changing the composition of the nutrient medium upon which the cells are grown, or by changing the surface of culture dish or by insertion of a specific gene.

I suppose you are wondering why go through all this trouble: well, ESC has the potential to cure and treat Parkinson's disease, diabetes, traumatic spinal cord injury, Purkinje cell degeneration, Duchenne's muscular dystrophy, heart disease, and vision and hearing loss.