[Hierarchically organized model of interconnected cellular and tissue mechanisms of calcium exchange between bone and blood].

The objective of this study was to propose, on the basis of the results of authors' own research and literature data, the hierarchically organized model of the interrelation of morphological mechanisms with the participation of biochemical bases of Ca2+ exchange between bone and blood. It is shown that osteocytes control the activity of main known mechanism of skeleton architecture remodeling (osteoclast-osteoblast remodeling, modeling, osteocyte remodeling etc.), that is the destruction and formation of mineral matrix component, thus influencing calcium turnover between bone and blood. The hierarchical organization of the mechanisms of this exchange is established. The first level of Ca2+ metabolism corresponds to the borderline between bone and takes place without bone matrix disintegration by paracellular energy-free Ca2+ diffusion from blood to bone and transcellular energy-dependent Ca2+ transfer from bone to blood. At the second level, calcium exchanger takes place at the borderline between between bone matrix and extracellular fluid by osteocyte remodeling during resorption or formation of the matrix of lacunar-canalicular system walls. The third level includes the mechanisms of osteoclast-osteoblast remodeling acting at the borderline between bone and blood. The mass of rapidly exchanging calcium pool was calculated to reach 58,5 g, thus being 11 times higher than previously suggected.