Cell Division in Endochondral Ossification

Abstract

1. The pattern of tritiated thymidine labelling in the cells of the epiphysial cartilage and metaphysis of the tibia in the rat is described for intervals of one hour to twenty-eight days after injection. 2. The region of dividing cells is defined and evidence given for a zone of reserve cells at the top of the cartilage columns. 3. The difficulties of quantitative grain count studies are discussed, and some approximate values are given for the generation time and mitotic cycle periods of the cartilage plate cells. 4. Some further evidence is given about the life cycles of the osteoblast and the osteoclast.

In vivo implantation of the mandibular condyle of the rat; an experimental investigation of the growth of the lower jaw

“…5.2. This observation is in agreement with Kember's (1960) findings for the direction of cell division in epiphyseal cartilage. The layer is thickest in the distal part of the condyle and tapers off towards the periosteum.…”

“…In epiphyseal cartilage on the other hand labelled chondrocytes were observed after 1 hr. (Kember 1960). These considerations seem to confirm Weinmann and Sicher' s (1964) view that in the condylar process the cartilaginous growth is of a depositional character, and that no proofs of an interstitial nature have as yet been forthcoming.…”

“…Quantitative assessment is based on counting the number of labelled cells or the number of grains per cell. (Young, 1962a, b;Kember, 1960;Blackwood, 1966;Tonna, 1960;Tonna & Cronkitc, 1961;Polke & Stallard, 1966). Injecting Зн-TdR during our experimental period enabled us to deter mine whether in the proliferating zone of the implants cell division per sists.…”

“…It is commonly assumed that in the zone of the cell columns there is interstitial growth of the cartilage as a result of frequent mitoses of chondrocytes and the formation of a cartilaginous matrix (Ham,1965;Weinmann and Sicher, 1955;Kember, 1960;and many others). On a basis of in vivo and in vitro experiments Holtrop (1964) holds that the zone of the small cartilaginous cells has a stimulating effect on this process.…”

“…Other authors think that undifferentiated connective-tissue cells, which invade such an area together with the blood vessels, are the predecessors of the osteoblasts lining the remains of the cartilaginous matrix. For these cells various names have been proposed, suchas spindle cells (Kember, 1960), reticular cells (Weinmann and Sicher, 1955) or osteoprogenitor cells (Young, 1962a). About the origin of the osteoclasts, too, different views are held (Tonna, 1960;Kember, 1960;Tonna and Cronkite, 1961;Maximow and Bloom, 1953;Weinmann and Sicher, 1955;Ham, 1965).…”