A comparative study of osteoblasts: In situ versus isolated specimens

Abstract

Osteoblasts and osteoclasts are known to adhere tenaciously to bone surfaces even when the fibrous periosteal covering is removed. Brush-smear isolates and in situ, whole bone mounts of the osteogenic periosteum on the inner and outer calvarial tables of young adult rats were examined at the light microscopic level after exposing the cells by removing the fibrous periosteum. Based on staining, enzymatic activity, and overall morphology, most of the cells could be classified as osteogenic in nature. However, detailed analysis revealed that some cells exhibited certain unique morphologic appearances that suggested the existence of subpopulations or variant forms of the conventional or prototypic osteoblast. Three variant forms were the large nucleate, small nucleate, and multinucleate osteoblast-like cells, the latter with nuclear numbers ranging from 2-10. The finding of all such forms in smears, short-term cell cultures, and in situ specimens greatly lessened the probability that the unusual forms were artifactual. Phase contrast microscopic studies and sectioning of cellular isolates for study at both the light and electron microscopic levels provided additional support for the existence of the multinucleate osteoblast-like cell. The small size of these osteoblast-like subpopulations and the orientation of the cells to the commonly used plane of section of most histologic bone specimens, particularly with the multinucleate type, could explain why they had escaped earlier detection.

Establishment of a clinically relevant large animal model to assess the healing of metaphyseal bone

“…The unique morphology and size of osteoblasts revealed their level of activity. Shape, size and arrangement of osteoblasts reflect their activity level (Ries et al, 1985;Zallone, 1977). The plump cuboidal-shaped osteoblasts characterised by a larger surface area and enriched cytoplasmic components, particularly the abundant rough endoplasmic reticulum and mitochondria, indicated their active involvement in the secretion of new bone matrix, whereas the flattened osteoblasts, characterised by several elongated cytoplasmic extensions with a poorly developed cytoplasm, possibly suggested a reduction in activity.…”

Transmission electron microscopy of bone tissue: A review

“…While all osteoblasts are osteogenic in nature, their shape, size, and arrangement suggest subpopulations exhibiting different levels of activity (Zallone 1977, Ries et al 1985. Numerous osteoblasts are very active, have a cubic shape (plump osteoblasts), and are arranged perpendicularly to the bone surface.…”