The Skeletal System: Bone Tissue - Chapter questions - Problem 1F

The periosteum is is a connective tissue layer that covers the surfaces of bones, except where articular cartilage is present. Periosteal coverings are double-layered: the outer layer is made up largely of tough irregular connective tissue, while the inner layer that makes contact with bone tissue is more cellular and vascular-- and has more elastic fibers. The periosteum protects the bone in several ways: it is a physical and a chemical barrier, as well as a defence against penetration by microbes. The mitotic activity of cells of the inner osteogenic layer of the periosteum is responsible for bone growth in thickness--but not in length. The blood vessels of the periosteum constitute one of the three sources of blood in long bones.. Ordinarily, they nourish the superficial layers of the cortex of the bone matrix; however, they also constitute a back-up resource, if there is a blockage in vessels in either of the two blood sources that supply bones. Perioustem promotes healing of bone fractures and provides points of attachment for tendons and ligaments. In addition, it should be remembered that the not only blood vessels, but also nerves that serve bones, travel through periosteum .