Calcium in Mineralized Tissues and Pathological Calcification

Crystal deposition is a widespread phenomenon in biology. It occurs in living organisms ranging from protozoa through to higher plants and animals. Various types of salts are involved, the commonest of which are insoluble calcium salts, particularly phosphates but also calcium salts of carbonate, oxalate and pyrophosphates. In vertebrates, mineralization usually takes place as part of physioloiclal processes, such as the calcification which occurs in teeth and in cartilage and bone. These processes are complex but orderly. Biological calicification is under the stimulatory control of matrix components (such as membrane bound vesicles) and macromolecules (such as collagen) as well as being subject to a system of inhibitory control mechanisms, involving small ions (e.g. pyrophosphate) and macromolecules (e.g. proteoglycans). In man there are several clinical disorders in which calcification may be defective. There are also many clinical conditions in which pathological deposits of calcium salts occur. This can occur as true ectopic bone, or as calcium deposits in visceral tissues or joints, or in the urinary tract as renal stones. The machanisms underlying most of these conditions are poorly understood and methods for treating them unsatisfactory.