What is the purpose of the endosteum?

• A. To cover the outer surface of bone
• B. To line the medullary cavity
• C. To form the lacunae
• D. To facilitate blood supply to cartilage

Answer: (B)

The purpose of the endosteum is to line the medullary cavity. The endosteum is a thin membrane composed of connective tissue that covers the internal surfaces of bones, particularly the areas surrounding the medullary cavity, which is the central cavity within long bones where bone marrow is stored. This lining is significant for several reasons: it plays a crucial role in the growth, repair, and remodeling of bone, as it contains osteoblasts (cells responsible for bone formation) and osteoclasts (cells responsible for bone resorption). By lining the medullary cavity, the endosteum also helps in maintaining a suitable microenvironment for hematopoiesis (the formation of blood cellular components) that occurs in the bone marrow. It serves as a critical structure in the overall health and functionality of the skeletal system.