A bone marrow stem cell is an immature undifferentiated cell found inside the bone marrow of most flat bones. It is said to be the mother of all blood cells as it can give rise to the red blood cells (RBC), the different types of white blood cells (WBC), and the platelets. Some studies suggest that the bone marrow stem cell is also capable of giving rise to other cells, like the endothelial cells, which line the walls of the blood vessels, or to become hepatocytes or liver cells. The bone marrow stem cell is also capable of self-renewal, a characteristic not present in most mature cells. This is important in replenishing the body with new blood cells as mature cells die after their given lifespan.
Before birth, the liver is the source of nearly all blood cells. A short time before a child is born, the bone marrow takes over this task. As a person matures, the source of bone marrow stem cells are limited to the flat bones, such as the hip bones, skull bones, ribs, vertebrae, sternum or breastbone, and shoulder blades.
There are two types of bone marrow: red marrow and yellow marrow. It is in the red marrow that most bone marrow stem cells reside. The yellow marrow is inactive, containing mostly fat cells, but is capable of converting to an active red marrow when the need arises, such as in some cases of blood disorders like anemia.
Some bone marrow stem cells are also found circulating in the peripheral blood, but these are capable of returning to the bone marrow in order to multiply and differentiate into specific cell types like RBC, WBC, or platelets. This allows bone marrow transplants to be performed by infusing donor stem cells into the recipient's blood, just like in a blood transfusion procedure. Stem cells can be harvested from the right donor through bone marrow aspiration or by filtering the peripheral blood for stem cells in a process known as apheresis.
Any diseases affecting the bone marrow can result in abnormalities in the production of blood cells in the body. Cancer patients undergoing procedures like chemotherapy and radiation therapy frequently have compromised blood cell production due to the effects of the treatments. Bone marrow stem cell transplantation is often needed in these cases to restore the bone marrow's supply of stem cells in order to continue production of blood cells as needed by the body.