| Popis: |
Until recently calcification was thought to be caused by the precipitation of bone mineral from a tissue fluid, which was temporarily super-saturated in respect to calcium and phosphate ions. In contrast to the precipitation reaction, the modern view assumes that calcification starts with the formation of a crystal seed in the organic matrix, upon which calcium and phosphate ions crystallize out from the metastable tissue fluid to form hydroxy-apatite. The problem of greatest interest is the nature of the seed, and how it is produced. There seem to be three main ideas regarding seed formation: collagen itself acts as the nucleating factor, chondroitin-sulphate is involved, phosphorylation of the matrix precedes calcification. While there is little doubt that crystal-seeding is the mechanism responsible for the initiation of calcification, the nature and control of the seed-forming reaction are still not sufficiently known. |
