The present paper is a comprehensive survey of the literature datu, particularly as far as those obtained by the authors are concerned, on the following aspects of osteocyte cytophysiology: the osteocyte life-span and ontogeny, the process of osteoblast-to-osteocyte transformation and the mechanism by which the osteoblast 'enters' the bone matrix to become an osteocyte, the shape, size and density of osteocyte lacunae and the extension of their canalicular network in relation with animal species and collagen fiber texture in the three different types of bone tissue (woven, parallel-fibred, lamellar), the osteocyte structure and ultrastructure with respect to cell age and metabolic activity of the skeletal region.
As regards the function performed by the osteocyte, this review points out that it has yet to be defined. In particular, the process of osteocytic osteolysis, put forward by Belanger and coworkers in 1963 and considered up to the early 1980s by most researchers to have been the main osteocyte function, can no longer be accepted as a proven phenomenon, since convincing evidence, accumulated over the last ten years, indicates that all the data reported by the 'osteolysers' in favour of their theory were either misinterpreted or misleading because they were recorded with wrong technical procedures.
The authors of this review do not absolutely exclude the possibility that osteocytes may, under certain circumstances, reabsorb the surrounding bone matrix, but they emphasize that this phenomenon has yet to be proved. They rather believe, on the basis of their recent findings and those reported in literature, that osteocytes might perform two different functions, according to their age. Preosteocytes and young osteocytes, close to osteoblastic laminae, are likely to be involved in the osteogenic processes: the former in the spatial organization of collagen fibers and the latter in recruiting osteoblasts committed to transforming into osteocytes. Adult and old osteocytes probably produce small molecules that may locally influence or even trigger the osteoclast-osteoblast system in the processes of internal and external bone remodeling.