blood cell production occurs in what section of the bone
Bone marrow Bone marrow is a semi-solid tissue which may be found within the spongy or cancellous portions of bones.[2] In birds and mammals, bone marrow is the primary site of new blood cell production or hematopoiesis.[3] It is composed of hematopoietic cells, marrow adipose tissue, and supportive stromal cells. In adult humans, bone marrow is primarily located in the ribs, vertebrae, sternum, and bones of the pelvis.[4] On average, bone marrow constitutes 4% of the total body mass of humans; in an adult having 65 kilograms of mass (143 lb), bone marrow typically accounts for approximately 2.6 kilograms (5.7Â lb).[5]