How It Works, From Embryo to Stem Cell: First an egg is feritilized or cloned to form an embryo. The embryo begins to divide.
1 to 5 Days: The Embryo divides again and again and takes shape as a sphere called a blastocyst. 
5 to 7 Days: By this time embryonic stem cells are visible and are capable of developing into any tissue in the body. 
Stem Line: The cells are removed and grown in a Petri dish. As they divide, they create a line of stem cells. 
Tissue Production: Using various recipes of nutrients and other factors, 
scientists hope to turn stem cells into any of the body's more than 200 tissues, 
such as: Pancreatic Islet Cells, could provide a cure for diabetes. Muscle Cells, could repair or replace a damaged heart. 
Nerve cells, could be used to treat Alzheimer's and Parkinson's diseases and repair spinal cord injuries.