The membrane lining the inner portion and marrow cavity of a bone is called?

• A. Periosteum
• B. Endocardium
• C. Pericardium
• D. Endosteum

Answer: (D)

Endosteum lines the inner surface of bone, including the medullary (marrow) cavity and the walls of the spaces within spongy bone. It’s a thin, vascular membrane that houses osteoprogenitor cells capable of becoming osteoblasts, supporting bone growth, remodeling, and repair from within the bone. This differentiates it from the periosteum, which coats the outer surface of bone, and from the heart-associated membranes—endocardium lining the heart chambers and pericardium surrounding the heart. Therefore, the membrane described is endosteum.