Tags: Anatomical Structure.
Bone marrow is the flexible tissue in the interior of bones. In humans red blood cells are produced by cores of bone marrow in the heads of long bones in a process known as hematopoiesis. On average bone marrow constitutes 4% of the total body mass of humans; in an adult weighing 65 kilograms (143 lb) bone marrow typically accounts for approximately 2.6 kilograms (5.7 lb).
