What is Bone Marrow?

Bone marrow consists of both red marrow and yellow marrow. It is spongy tissue located in the center of some large bones in the body and functions to produce new blood cells. It also plays a vital role in fighting infections and cancers. Bone marrow is also known as myeloid tissue and is red, soft, semi-solid, gelatinous and mostly found in the axial skeleton, such as hip and thigh bones. It is very vascular as it contains many blood vessels and capillaries. It makes more than 200 billion new blood cells daily.

Deep inside the bone marrow contains a type of cell known as the mesenchymal stem cells (MSCs) that has the capability to differentiate into cells that produce bone, cartilage, fat, muscle, and more. A wide range of cell progenitors were also found by researchers in the bone marrow. This has led to the understanding and identification of different blood and autoimmune diseases. This is also why access to normal bone marrow is important in the advancements of research and studies on treatment of disease.


Why is bone marrow important?


Healthy bone marrow is essential to health. When there is disease that affects the bone marrow to the point where it can no longer function effectively, a marrow or cord blood transplant can be the only hope for a cure. The normal bone marrow architecture can be disrupted by malignancies or infections that may cause a decrease in blood cell production. For example, there are many individuals with blood disorders such as leukemia, lymphoma, sickle cell anemia, and other life-threatening disease that rely on bone marrow or cord blood transplants to stay alive. A bone marrow transplant can:

  • Replace diseased bone marrow

  • Regenerate a normal immune system that fights existing or residual cancers or infection

  • Restore normal function of bone marrow after treatment of malignancy (chemotherapy / radiation)

  • Replace bone marrow with healthy functioning bone marrow to prevent further damage from genetic disease process

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Types of bone marrow

At birth, all bone marrow is red. With increasing age, more red bone marrow is converted to the yellow type. On average, adults have about 2.6kg of bone marrow with half of it being red and the other half yellow. There are two types of bone marrow:


Red bone marrow, also known as "hemopoietic" –

  • functions to produce blood cells, white blood cells, and platelets.

  • produces 60-70% of lymphocytes.

  • functions to eliminate old red blood cells, sharing the responsibility with both the liver and spleen.

  • The red color is obtained from the hemoglobin found in the erythroid cells.

  • Once the hematopoietic cells mature, it migrates into the sinusoids to enter the circulation.

  • is highly vascular

  • For adults, it is typically found in flat bones such as hip bone, breast bone, skull, ribs, vertebrae, shoulder blades, while in children, it is mostly found in the cancellous material at ends of long bones (femur and humerus).

  • Once an individual reaches old age, almost all the bone marrow is yellow by then.


Yellow bone marrow, also known as "stromal" -

  • functions to produce fat, cartilage, and bone as it stores adipocytes that has triglycerides, serving as a source for energy

  • The fat in the marrow is different compared to the fat in the rest of the body and is the last fat lost due to starvation.

  • It obtains its yellow color from the carotenoids found in the fat droplets in the fat cells.

  • is less vascular compared to red bone marrow

  • can be converted back into red bone marrow in the event of severe blood loss to increase blood cell production

  • can be found in the hollow interior of long bones.



There are two types of bone marrow: red marrow and yellow marrow. Both types of bone marrow play important albeit distinct roles in the body. The most important function of the red bone marrow is the production of blood cells and with age, more red bone marrow is gradually converted to yellow bone marrow that functions to store energy. It also has other functions such as fighting infection and cancer cells. Hence, a normal bone marrow is essential for health.



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