Chapter 1 - General Outlines of Bone Tissue Metabolism

Abstract

This chapter focuses on bone tissue metabolism. Bones are organized on two levels: (1) as organs and (2) as a tissue. As organs, they are particular elements of the skeleton adapted to withstand stresses; as a tissue, they form a highly specialized connective tissue composed of cells embedded in an interstitial substance, which includes the organic framework or matrix and the mineral. The chapter discusses the molecular structure and metabolism of the major parts of bone, namely, cells, organic matrix, and inorganic salts. Bone cells are organized in three compartments: (1) proliferating, (2) functional, and (3) a final-stage compartment. The interstitial organic substance or matrix consists of two major components: (1) collagen and (2) ground substance. The degradation of bone collagen to peptides and amino acids is mediated by proteolytic enzymes. The ground substance in which the cells and collagen are embedded consists of proteoglycans and glycoproteins. The time-dependent changes in the content of proteoglycans are because of their half-lives. The catabolism of sulphated glycosaminoglycans depends on the desulphation processes, followed by the degradation of the desulphated polymer. The inorganic portion of bone contains two major mineral phases: (1) amorphous or noncrystalline calcium phosphate and (2) crystalline bone apatite. Both the amorphous calcium phosphate and crystalline apatite are strongly hydrated; the volume of hydration shell is several times greater than that of mineral.