Which type serves as the primary production centers for red blood cells in adults?

• A. Long bones
• B. Short bones
• C. Flat bones
• D. Sesamoid bones

Answer: (C)

Red blood cells are produced in red bone marrow through hematopoiesis. In adults, this production centers mainly in flat bones of the axial skeleton. Flat bones such as the sternum, ribs, iliac crests of the pelvis, skull bones, and vertebrae contain abundant red marrow that continuously generates RBCs. As people age, red marrow in long bones is largely replaced by yellow marrow (fat), so long bones are no longer the primary sites for RBC production. Briefly, some hematopoietic activity can remain at the ends of long bones, but the major production centers in adults are the flat bones.