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Stem Cells

A woman peering into a microscope
“A few short years ago, it was rare to meet someone who knew what I meant when I said I was a stem cell biologist. Now, virtually everybody's heard about stem cells and has an opinion about them.”
—Dr. Jack Kessler

A close-up of a cell, with numerous smaller branches radiating from a blurry, large center
Embryonic stem cell
Photo: Nissim Benvenisty/PLoS Biology

What Are Stem Cells?

Stem cells are basic, or undifferentiated, cells that have no specific function in the body. Their name is derived from the fact that every cell in the body stems from this type of cell. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell or a brain cell.

There are three characteristics of all stem cells. They can divide indefinitely and are the only type of cells, besides cancer cells, that have the capacity to divide forever. Stem cells are also capable of self-renewal, and can make identical copies of themselves indefinitely. In addition, stem cells have the potential to become any other kind of cell in the body.

Types of Stem Cells

Embryonic stem cells are derived from the inner cell mass of the blastocyst, an early-stage embryo that is approximately four to five days old in humans and consists of 50 to 100 cells. Embryonic stem cells can develop into each of the more than 200 cell types in the adult body when given sufficient and necessary stimulation for a specific cell type.

Adult stem cells are any cell in a developed organism that has two properties: the ability to divide and create another cell like itself and also divide and create a cell more differentiated than itself. Also known as somatic stem cells, they can be found in children and adults. Cord blood stem cells are found in the umbilical cord at birth and can produce all of the blood cells in the body. Cord blood is currently used to treat patients who have undergone chemotherapy to destroy their bone marrow due to cancer or other blood-related disorders.

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