A Three-dimensional ultrastructural study of osteoid-osteocytes in the tibia of chick embryos.

Osteoid-osteocyte are active cells engaged in organic matrix secretion and calcification. Like osteoblasts, their activity seems to be polarized towards the mineralization front, as shown by the presence of cytoplasmic processes on their mineral-facing side and by the position of the nucleus toward the vascular side of the cytoplasm. Cellular processes directed towards blood vessels appear only at a later stage, i.e. when the mineralization start to spread all around the cell.The asynchrony in formation together with the observed differences in morphology suggest the hypothesis that the cellular processes of the mineral-facing side are mainly involved in bone formation and those of the vascular side in cell nutrition