As their names suggest, adult and embryonic stem cells come from different places -- but that's not their only difference.

Embryonic stem cells are extracted from a human embryo a few days after fertilization in a process that destroys the embryo. Adult stem cells are isolated from human tissue after birth, such as bone marrow, adipose (fat) cells or even blood from newborn babies' umbilical cords.

Embryonic stem cells can divide for a year or more in a laboratory without becoming specialized cells -- a process called self-renewal. One stem cell can produce hundreds of genetically identical stem cells, which is then called a stem cell line. Most adult stem cells typically can't self-renew for more than a couple of weeks.

But the biggest difference in potential between adult and embryonic stem cells comes down to their developmental capacity -- their ability to give rise to other, more mature types of cells.

The most flexible type of stem cells are those that are totipotent, which are considered the "master" cells of the body because they contain the genetic information necessary to create all the cells in the body. The fertilized egg is an example of a totipotent cell.

Pluripotent stem cells, which come from embryos and fetal tissue, have the potential to develop into all of the more than 200 different known cell types in the adult body -- except the placenta.

Embryonic stem cells were at first thought to be pluripotent. But research has found that embryonic stem cells derived from mice are totipotent, and recent studies with human embryonic stem cells are likely also totipotent, according to Dr. Dan Kaufman, a researcher at the University of Minnesota's Stem Cell Institute.

Until recently, adult stem cells were thought to have a more limited developmental capacity. They were thought to be multipotent -- that is, they have the ability to become several types of cells within a specific type of tissue or organ. The developmental restriction means that an adult stem cell in the bone marrow can develop into a red blood cell, a blood platelet or a white blood cell, but generally not a skin cell or brain cell.

However, research has recently suggested that some adult stem cells -- such as those in the bone marrow -- may be more flexible than previously thought, with pluripotent properties.

Research involving adult stem cells has been conducted for decades, while embryonic stem cell research is in its infancy. Although adult stem cells have been used successfully in some human therapies, neither adult nor embryonic stem cells have been used to treat and cure diseases such as diabetes, Parkinson’s disease or heart disease.

Clinical successes of adult stem cell use in bone marrow transplantation has shown stem cell-based therapies can save lives. The main interest and goal of stem cell researchers is to expand this success to a greater number of diseases, Kaufman said. For some diseases, embryonic stem cells may be a better starting point, and for others adult stem cells may be more suitable.

A major goal is to compare and contrast adult and embryonic cell populations to find the most effective therapy, he said.

"It's not an 'either/or' situation; the greatest likelihood of success will come by pursuing all avenues," Kaufman said.