The tubular shaft forming the long axis of a typical long bone is called the

• A. Diaphysis
• B. Epiphysis
• C. Metaphysis
• D. Epiphyseal line

Answer: (A)

The tubular shaft forming the long axis of a typical long bone is the diaphysis. This central, cylindrical portion runs along the length of the bone and is built mainly from compact bone, which gives strength while keeping the bone lightweight. Inside the diaphysis is the medullary (marrow) cavity, lined by endosteum, which in adults often contains yellow marrow.

The ends of the bone are the epiphyses, which contain spongy bone and are involved in joint formation and cartilage articulation. The region between the diaphysis and each epiphysis is the metaphysis, where growth in length occurs during development. When growth stops, the epiphyseal growth plate ossifies and leaves an epiphyseal line.