What is the shaft of a long bone called?

• A. Epiphysis
• B. Medulla
• C. Metaphysis
• D. Diaphysis

Answer: (D)

Understanding long-bone anatomy helps connect function with structure. The shaft of a long bone is called the diaphysis. It runs between the two ends (the epiphyses) and is mainly composed of dense cortical bone with a hollow center known as the medullary cavity, which houses bone marrow. This arrangement gives the diaphysis the strength needed for weight-bearing and lever action. The ends are the epiphyses, and the region between the shaft and ends is the metaphysis, where growth occurs in developing bones. The medullary cavity inside the diaphysis is not the shaft itself but the hollow interior within it. So, the shaft of a long bone is the diaphysis.