TedEd: How bones make blood

A TedEd by Melody Smith

Your body has trillions of blood cells circulating inside you. All of these originate in your bones. Bones may seem hard, but they're actually porous inside, allowing blood vessels to enter. Most of the bone is filled with soft bone marrow. The most important part of this is blood stem cells. These multiply many times, turning into red and white blood cells, and platelets. They go out into the blood stream through capillaries. This is why many blood cancers occur in bone marrow. If the stem cells have a mutation, they could produce malignant blood cells, which are bad for the body. For patients with diseases like leukemia and lymphoma, their best bet at survival is a bone marrow transplant. To do this, stem cells are taken from a donor in one of two days. The first is by extracting blood and then separating stem cells, the second by direct extraction from bone. Chemotherapy or radiation are used to kill existing bone marrow, then the donor's is transplanted in the patient. This can also cause graft-vs-tumor activity. This is when the transplanted immune cells from the donor wipe out cancer cells that the patient's immune system couldn't. However, there could also be adverse effects. Graft-vs-host disease occurs when the donor's immune cells begin attacking the patient's organs, causing life-threatening conditions. This occurs in about 30-50% of people whose donor isn't an identical twin. To prevent this, patients can take immunosuppressants, or immune cells can be removed from the donor's cells. But if they overcome this obstacle, they face the possibility of their own immune system denying entry for the new stem cells. In order to find the best donor, genetic samples are taken and key strands that control the immune system are matched. For this reason, siblings and close relatives are often the best donors, as these genes are passed down. If you want to donate, go to join.bethematch.org to enter yourself in the registry. The donating process is just giving some blood.