The diaphysis of a bone is which part?

• A. The end of a long bone
• B. The joint surface
• C. The cartilage layer between epiphysis and diaphysis
• D. The shaft of the bone

Answer: (D)

The diaphysis is the shaft of a long bone—the long, cylindrical middle section that provides strength and leverage. It is mainly compact bone surrounding the central medullary (marrow) cavity. The ends of the bone are the epiphyses, which form joints and contain spongy bone with articular cartilage on the joint surface. In growing bones, the cartilage layer between the epiphysis and diaphysis is the epiphyseal plate (growth plate), which allows lengthwise growth (epiphyseal line in adults). So the diaphysis is the shaft.