Bone marrow

Bone marrow is a soft gelatin like tissue found in the central cavities of long bones and some short bones. It contains Stem cells and it produces most of the new red blood cells in the human body. There are two types of bone marrow. Red bone marrow (which is also known as myeloid tissue) and yellow bone marrow (fatty tissue).

What is bone marrow?

Bone marrow is the gelatinous, spongy substance in found in the cavities of long bones. It contains two types of stem cells. A stem cell is an immature cell which can change into a new specialised cell as required. The two types of stem cell found in bone marrow are:

  1. Hematopoietic cells which can be used to make all the blood cell types in the body with over 200 billion new red blood cells produced everey day in healthy tissue.
  2. Stromal cells which can produce fat, cartilage and bone.

Red blood cells, platelets and most white blood cells arise in the red bone marrow whilst some white blood cells develop in the yellow marrow. Yellow marrow is yellow because it has a much higher number of fat cells. Red blood cells are important in sports performance as they carry oxygen around the body. Red marrow is not found in all the bones of the human body. It is found mainly in the flat bones, for example the hip bone, vertebrae and shoulder blades. Two types of osseous tissue form bones, compact bone and cancellous (spongy) bone. Red bone marrow is also found in the cancellous material found at the ends of the long bones (the femur and humerus).

How does bone marrow produce red blood cells?

A decrease in oxygen in the blood is detected by the kidneys which then secrete the hormone called erythropoietin (commonly known as EPO). This hormone is found naturally in the body and stimulates erythropoiesis, the process by which red blood cells (erythrocytes) are produced in the red bone marrow. The body regulates the process of erythropoiesis so that red blood cells are produced at a rate that is equal to the destruction of red blood cells. This enables the body to sustain adequate tissue oxygen levels.

Blood doping

A good example of how this works is when an athlete has to aclimatise if they travel to a higher altitude when undergoing altitude training. The body naturally makes more red blood cells to increase the oxygen levels in the blood. However, if additional amounts of the hormone EPO are taken artificially then red blood cells can increase artificially. This process is known as blood doping and is banned in most sports. It was popular among elite level cyclists and middle distance / endurance runners as a way of enhancing performance.

Bone Marrow Transplants

Bone marrow transplants are given to people with diseases of the blood, bone marrow and certain types of cancer. The procedure can have many complications so is only used on people with life threatening diseases. The process involves harvesting the healthy stem cells to replenish the bone marrow of the patient. These new stem cells then take over the production of healthy new blood cells.

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