What Are Stem Cells?

Research on stem cells is advancing knowledge about how an organism develops from a single cell and how healthy cells can replace damaged cells in adult organisms.

Definition of Stem Cells

Stem cells have two important characteristics that distinguish them from other types of cells. Firstly they are unspecialized cells and secondly, under certain physiologic or experimental conditions, they can be induced to become cells with special functions.


All stem cells have three general properties


  • They are unspecialized;
  • They can give rise to specialized cell types;
  • They are capable of dividing and renewing themselves for long periods

Stem cells may replicate many times in a process called proliferation. If the resulting cells continue to be unspecialized, the cells are said to be capable of long-term self-renewal. Also, stem cells do not have any tissue-specific structures, therefore unspecialized stem cells can give rise to specialized cells, including heart muscle cells, blood cells, or nerve cells by a process called differentiation.

Blood stem cells are one of several types of stem cell. Healthy blood stem cells are vital because they replace our supply of red blood cells, white blood cells, and platelets. Red blood cells carry oxygen throughout the body, white blood cells fight infection, and platelets clot blood (control bleeding) when the skin or other tissue is cut.

When a person's blood stem cells become diseased or cancerous, it is a life-threatening situation. Often, the only hope for a cure is a blood stem cell transplant, which replaces the patient's diseased cells with healthy new cells. For the transplant to be a success these cells must match the patient's own cells as closely as possible.

The cells used in blood stem cell transplants come from three main sources: bone marrow, peripheral (or circulating) blood, and the umbilical cord of newborn babies (cord blood). In the case of bone marrow and peripheral blood stem cells, an adult donor donates the cells. Umbilical cord blood stem cells are collected when a baby is born and are stored for future use.


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