<P> Bone marrow is a semi-solid tissue which may be found within the spongy or cancellous portions of bones . In birds and mammals , bone marrow is the primary site of new blood cell production or hematopoiesis . 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 . 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 ( 5.7 lb ) . </P>
<P> Bone marrow is a semi-solid tissue which may be found within the spongy or cancellous portions of bones . In birds and mammals , bone marrow is the primary site of new blood cell production or hematopoiesis . 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 . 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 ( 5.7 lb ) . </P>
blood cell production occurs in what section of the bone
blood cell production occurs in what section of the bone
bone marrow
bone marrow