Red marrow is more active in which bones of children?

• A. Long bones of limbs
• B. Flat bones
• C. Irregular bones
• D. All bones equally

Answer: (A)

Red marrow, where blood cells are produced, is especially active in the long bones of the limbs during childhood. These bones are sites of rapid growth, and their marrow cavities house a large amount of hematopoietic tissue to meet the body's increasing needs for red cells, white cells, and platelets. While flat and other bones contain red marrow as well, the level of activity is greatest in the long bones in children. As people age, red marrow activity shifts and becomes more limited, with yellow marrow becoming more prevalent in the limbs and red marrow persisting mainly in the axial skeleton and some proximal ends of long bones.