What Is Bone Marrow

Marrow is a soft tissue of the medullary cavities (medullar = the centre of an organ) of the bone.

There are two types of marrow. Yellow marrow consists mostly of fat, and red marrow consists of blood-forming cells and is the only site of blood formation in adults.

Children’s bones have proportionately more red marrow than adults as they are in their growth and development stage. As a person ages, red marrow is mostly replaced with yellow marrow. In adults, red marrow is confined to the bones in the central axis of the body (e.g. pelvis and skull) and in the most proximal parts of the limbs.

Some types of leukaemia and genetic immune deficiency diseases can be treated with a bone marrow transplant containing blood stem cells - which are blank cells that can turn into specialised cells such as blood cells during hematopoiesis.