BONE

rigid body tissue consisting of cells embedded in an abundant, hard intercellular material. The two principal components of this material, collagen and calcium phosphate, distinguish bone from such other hard tissues as chitin, enamel, and shell. The functions of bone include (1) structural support for the mechanical action of soft tissues, such as contraction of muscles, expansion of lungs; (2) protection of soft parts, as by the brain case; (3) provision of a protective site for specialized tissues such as the blood-forming system (bone marrow); and (4) a mineral reservoir or sink, whereby endocrine systems regulate the level of calcium and phosphate in the circulating body fluids. rigid body tissue consisting of cells embedded in a hard intercellular matrix. Bone exists in vertebrates only. Bone has many functionsit serves as a structural frame to support the body; it enables movement by providing a point of attachment for the muscles and by serving as a system of levers; it protects the brain, spinal cord, and the soft internal organs; it houses the blood-forming system (red bone marrow); and it acts as a reservoir for the mineral calcium, which is vital to many body processes. Additional reading F.C. McLean and M.R. Urist, Bone: Fundamentals of the Physiology of Skeletal Tissue, 3rd ed. (1968), a comprehensive survey of bone structure and metabolic function; H.M. Frost (ed.), Bone Biodynamics (1964), a series of authoritative essays on topics of chemistry, structure, function, and disease; W.H. Harris and R.P. Heaney, Skeletal Renewal and Metabolic Bone Disease (1970), a review of skeletal remodelling processes, with emphasis on their control mechanisms and on methods of measuring remodelling in the living skeleton; K. Rodahl, J.T. Nicholson, and E.M. Brown (eds.), Bone as a Tissue (1960), a series of essays and reviews on topics of bone structure, physiology, and disease; and C.L. Comar and F. Bronner (eds.), Mineral Metabolism, vol. 1B, 2A, and 3 (196069), exhaustive and definitive reviews of the chemistry and metabolism of the principal mineral components of bone. See also Marshall R. Urist (ed.), Fundamental and Clinical Bone Physiology (1980), which covers bone diseases as well. Two works useful for understanding the functional aspects and structural adaptations of bone are G.H. Barnett, Joints and Movement in F. Goldby and R.J. Harrison (eds.), Recent Advances in Anatomy, 2nd ed., ch. 12, pp. 404422 (1962); and M.C. Hall and D.S. Kinoshita, Architecture of Bone (1966).