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  • 1
    ISSN: 1432-0827
    Keywords: Parathyroid hormone ; Osteoclasts ; Electron microscopy ; Morphometry ; Metaphysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The effects of parathyroid hormone (PTH) on the size of the osteoclasts, nuclei, ruffled borders, and clear zones in long bones of thyroparathyroidectomized (TPTX) rats were quantitated as a function of time. These data were compared with the number of osteoclasts in the bone and with plasma calcium levels. A significant increase in the average size of the ruffled borders was demonstrated 30 min after injection of 50 U of purified bovine PTH, and of the clear zones 30–90 min after PTH. This was followed at 90 min by an increase in the average size of the cells. The sizes of ruffled borders and clear zones dropped sharply to control levels after 6 h, whereas the size of the cells remained elevated up to 12 h and returned to control values at 24 h. Plasma calcium levels were increased, but not significantly, between 30 min and 6 h. An increase in the number of osteoclasts was significant after 12 h. Removal of the parathyroid glands did not diminish the normal activity of osteoclasts. In animals with intact glands injection of 50 U of PTH did not cause a significant change in cell size or resorbing apparatus. It is concluded that PTH acts to rapidly stimulate the bone resorptive activity of osteoclasts and to cause a delayed increase in their number.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 9 (1972), S. 140-151 
    ISSN: 1432-0827
    Keywords: Cartilage ; Epiphysis ; Cell ; Differentiation ; Endoplasmic reticulum ; Mitochondria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Une étude ultrastructurale de chondrocytes hypertrophiques est rendue possible par suite d'une meilleure méthode de fixation. Contrairement à l'opinion qui veut que les cellules hypertrophiques meurent, nos résultats suggèrent nettement une activité cellulaire allant du début de la croissance de la cellule au stade où la lacune s'ouvre. La séquence des altérations cellulaires est décrite, en allant de l'augmentation de l'ergastoplasme à la présence de ribosomes libres et de granules denses aux électrons dans les mitochondries. Les diverses fonctions possibles de la cellule sont décrites. Il est possible que les chondrocytes hypertrophiques se transforment en cellules osseuses.
    Abstract: Zusammenfassung Eine verbesserte Fixationsmethode ermöglichte die Untersuchung der Feinstruktur des hypertrophischen Chondrocyten. Im Gegensatz zur allgemeinen Annahme, daß die hypertrophischen Zellen absterben, weisen unsere Resultate deutlich darauf hin, daß die Zellaktivität vom Moment der Zellvergrößerung bis zum Stadium, in welchem die Lacunen aufbrechen, vorhanden ist. Der Ablauf der Veränderungen innerhalb der Zelle wurde beschrieben, wobei die hervorstechendsten Charakteristika die Zunahme des endoplasmatischen Reticulums, das Auftreten von vielen freien Ribosomen und das Vorkommen von elektronenmikroskopisch dichten Granula in den Mitochondrien waren. Die möglichen Funktionen der Zelle wurde besprochen. Es ist äußerst interessant, daß dadurch die Hypothese, wonach die hypertrophischen Chondrocyten schließlich zu Knochenzellen werden, unterstützt wird.
    Notes: Abstract A study of the ultrastructure of the hypertrophic chondrocyte has been made possible by an improved method of fixation. In contrast to the general belief that the hypertrophic cells die, our results strongly suggest cell activity from the beginning of enlargement of the cell up to the stage where the lacuna breaks open. The sequence of alterations within the cell have been described, with the increase of endoplasmic reticulum contents, the appearance of many free ribosomes and the occurrence of electron-dense granules in the mitochondria as the most prominent characteristics. The possible functions of the cell have been discussed. Most interesting is the support for the hypothesis that hypertrophic chondrocytes may ultimately become bone cells.
    Type of Medium: Electronic Resource
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