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Quantitative investigation on osteocyte canaliculi in human compact and spongy bone.
No full textBy means of the two techniques (reflected polarized light and SEM) used in previous investigations (Remaggi et al., Calcif. Tissue Int., suppl. 3b, 26, 1983), the number of canaliculi departing from osteocyte lacunae was counted in compact and spongy bone of human tibiae from normal subjects of different ages.The statistical analysis of the results indicates that in both compacta and spongiosa the extension of the canalicular network is significantly greater in woven than in lamellar bone. In the latter, moreover, the number of canaliculi per unit lacunar surface appears to be proportional to the size of the lacunae and greater in lacunar walls facing the vascular source than in the opposite walls facing the cement line. This occurs in secondary osteons and in fragments of spongy trabeculae outlined by reversal lines.These results strongly suggest the hypothesis that the metabolic activity of the osteocytes differs according to the type of bone tissue and in different skeletal regions
Histomorphometric study on the osteocyte lacuno-canalicular network in animals of different species. I. Woven-fibered and parallel-fibered bones.
No full textA comparative histomorphometric study was carried out on the extension of lacuna-canalicular network in two types of bone tissue, i.e. woven-fibered and parallel-fibered, in shaft bones of various animals (frog, chicken, rabbit, dog, bovine, horse and man), with the aim to understand whether the distribution of osteocyte network is mainly related to the organization of the collagen fibres or to the animal species
Quantitative evaluation on osteocyte canalicular density in human secondary osteons.
No full textOsteocyte canalicular density (OCD) was evaluated at different levels of the wall of human secondary osteons, in subjects of different ages, to find out whether any correlation exists between the extension of the canalicular network and the exponential decrement of the appositional growth rate (AGR), which has been shown to occur during osteon formation. Scanning electron microscopy (SEM) was used to count the number of canalicular openings per unit surface on large Haversian canals of forming osteons as well as on small canals of completed osteons. Reflected polarized light microscopy (RPL) enabled the number per unit length of canaliculi to be counted at different concentric levels of the osteons. The results of both techniques agree in showing that, in the subjects examined, OCD does not change significantly throughout the osteon wall. Since no correlation exists between OCD and AGR, it follows that osteoblast flattening, which was shown to occur in parallel to the decrement of the rate of concentric bone deposition, does not seem to depend primarily on the number of osteoblast-osteocyte contacts, but on other factors
Morphometric investigation on osteocytes in human auditory ossicles
No full textAn osteocyte lacunae differential count (1-lacunae with live osteocytes, 2-lacunae with degenerating osteocytes, 3-empty lacunae) was carried out on ear ossicles and clavicles from cadavers as well as on stapes removed by stapedotomy. The distance of the three types of lacunae from the vascular source was also determined by a computer-assisted light microscope. Results showed that the delayed fixation of bone from cadavers does not significantly interfere with osteocyte preservation, at least with the scope of this investigation. The results of osteocyte differential count show that the number of empty lacunae and lacunae with degenerating osteocytes: (a) is significantly higher in ear ossicles than in clavicles, (b) increases with age, (c) is higher in stapes than in incuses and mallei, (d) increases with the distance from the vascular sources in both ear ossicles and clavicles. Additionally it appeared that the process of osteocyte degeneration in ear ossicles is very rapid and widespread, over 40% of the cells being dead within the 2nd year of age. In the light of the recent literature and personal findings, which ascribe to osteocytes the function of mechanical detectors, and considering that bone remodeling occasionally occurs in ear ossicles, it is postulated that osteocyte death in these bones could be a programmed phenomenon (apoptosis?), due to which they lose the ability to react to strains and stresses and achieve the structural stability they need to perform their peculiar stereotyped function
Histomorphological and chemico-physical analyses of the mineral matrix of micropetrotic human bone
No full textMicropetrotic areas of human bone were analyzed with reference to their distance from blood vessels and to the age of the subjects. Undecalcified bone sections were treated with various solvent, soaking and etching substances to establish the nature of the material occluding the osteocytic canalicular cavities, and were examined by means of microradiographic and microdurimetric methods and X-ray microanalysis to evaluate the degree of mineralization in the bone matrix. Since it was only after strong etching with HCl that the canalicular network became visible under light and scanning electron microscopy, it is clear that the debris filling the-canalicular network consists almost entirely of mineral substance. The degree of mineralization of micropetrotic bone is high because it is always a more mature type Of bone, but the mineral content of the matrix and the Ca/P ratio do not differ significantly from those of neighbouring bone where the canalicular network is fully pervious
Modificazioni della struttura dell'osso osteonico nella fluorosi industriale [Changes in the structure of osteonic bone in industrial fluorosis]
No full textE stata condotta un'indagine comparativa al microscopio ottico a luce ordinaria e a luce polarizzata su sezioni centrodiafisarie di ossa metacarpali di bovini affetti da fluorosi industriale.I reperti istologici osservati concordano con quelli riportati in letteratura per quanto concerne sia la disorganizzazione del collagene sia la presenza di lacune osteocitarie anomale negli osteoni secondari. I risultati delle nostre osservazioni, in accordo con i dati morfometrici, indicano però che entrambi i tipi di lacune patologiche già descritti in letteratura, le cosiddette «mottled» ed «enlarged» lacune, sono per forma, densità e dimensioni del tutto identiche alle lacune che si trovano nell'osso a fibre intrecciate normale e che inoltre sono sempre localizzate in porzioni di osteoni secondari dove il collagene non è organizzato come di norma a lamelle ma a fibre intrecciate.Se ne deduce, contrariamente a quanto sostenuto da altri autori, che ambedue i tipi di lacune patologiche sono da considerarsi il risultato di una stessa noxa, ossia di una interferenza del fluoro sul metabolismo degli osteoblasti, con conseguente anomala deposizione di osso a fibre intrecciate negli osteoni secondari.A comparative investigation under ordinary and polarized light was carried out on metacar-pal bones from normal and fluorotic bovines. The histologic findings agree with those reported in literature as regards the disorganisation of collagen and the presence of abnormal osteocyte lacunae in the secondary osteons (Fig 1). Three types of pathologic haversian systems were observed: osteons with large lacunae near the cement line, osteons with «mottled lacunae», and osteons with lacunae showing an intermediate aspect (Fig. 2). Microradiographic analysis showed patches of lower degree of radiopacity in «mottled» areas, but the former appears of lower extension than the latter (Fig. 2b). The results of our observations, in agreement with the morphometric data (Fig 6), show that both types of pathologic lacunae described in literature (i.e. the so-called «mottled» and «enlarged» lacunae) are identical in shape, size and density with the lacunae found in normal woven bone (Fig 7); moreover, that these lacunae are always located in portions of secondary osteons where the collagen is not organized in lamellae, as normally, but in woven fibres (Fig 3, 4).As against what has been maintained by other authors, we conclude that both types of abnormal lacunae must considered the result of an identical pathological phenomenon: that is to say, an interference by fluoride in the metabolism of the osteoblasts, with a consequently abnormal deposit of woven bone in the secondary osteons
Activity of osteoclasts and osteocytes in compact human bone at various ages, both with and without osteoporosis.
No full textAs part of a programme of research designed to assess the respective roles of osteoclasts and osteocytes in the processes of bone resorption, the metabolic activity of these cells was evaluated indirectly by a morphometric method in the compact bone of human tibias from subjects of various ages, both normal and those affected by osteoporosis. Statistical analysis of the quantitative data was in agreement with the microradiographic examination of the sections, and showed that whereas the intensity of osteoclastic resorption varied in the various subjects according to age, periosteocytic osteolysis--in the classical sense of a phenomenon involving widening of the lacunae detectable with the optical microscope--did not occur in compact bone whether it was normal or highly porotic
Size and density of osteocyte lacunae in different regions of long bones.
No full textSize and density of osteocyte lacunae were evaluated at different levels of long bones to investigate whether or not the proportion of bone tissue occupied by osteocytes changes in skeletal regions, characterized by clear-cut differences in bone turnover rates. Statistical analysis of the results shows that the mean cross-sectional area of osteocyte lacunae (C) is lowest in compact bone of diaphysis and metaphysis, highest in spongy bone of metaphysis and epiphysis. On the contrary, the mean surface of bone tissue surrounding each osteocyte (T = bidimensional osteocyte territory, indirectly calculated from the number of lacunae/mm2 of bone) is largest in compact bone of diaphysis, smallest in metaphyseal spongiosa, and shows intermediate values in the cortex of metaphysis and in epiphyseal spongiosa. The proportion of bone tissue occupied by osteocyte lacunae (% C/T) appears to follow at different levels of long bones, the same pattern recorded for the data of bone turnover rate, by the tetracycline labeling technique: it is lowest in mid-diaphyses, highest in metaphyses, and intermediate in epiphyses. On the basis of these findings, it is suggested that the action exerted by osteocytes on the surrounding calcified matrix, whatever the function of these cells, is not uniform throughout the skeleton and is to some extent correlated with the activity of the other bone cells-osteoblasts and osteoclasts.The signifìcance of some of the data reported is also discussed in relation to investigations of periosteocytic lacunar morphometry
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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