What are the periosteum and endosteum, and what are their main functions in bone structure?
The periosteum is a dense irregular connective tissue covering the outer surface of bone, containing blood vessels, nerves, and serving as an attachment point for tendons and ligaments. It is anchored to bone by perforating fibers. The endosteum lines the inner surfaces of bones, such as the medullary cavity and spongy bone, and consists mainly of osteoprogenitor cells important for bone remodeling and repair.