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  • Articles  (43)
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  • Springer  (43)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 35 (1983), S. 773-777 
    ISSN: 1432-0827
    Keywords: 1,25-(OH)2-D3 ; Hypophysectomy ; Growth hormone ; Phosphorus ; 31P NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary In order to evaluate a possible role for tissue phosphate or phosphorylated compounds in mediating the increase in plasma 1,25-(OH)2-D3 levels during dietary phosphate deprivation, measurements of total and acid-soluble renal cortical phosphate content have been made in both intact and hypophysectomized (hypox) rats eating a normal diet and also after four days of dietary phosphate deprivation. Similar measurements were also made in phosphate-deprived hypophysectomized rats replaced with growth hormone (GH). Total and acid-soluble renal cortical phosphate content averaged 81±8 µmol/g and 4.1±0.6 µmol/g, respectively, in intact rats eating the normal diet and were not significantly altered after phosphate deprivation despite a fall in plasma phosphate of about 40% and a fourfold increase in plasma 1,25-(OH)2-D3 levels. Total and acid-soluble renal cortical phosphate content levels were higher in hypox rats, averaging 92±8 µmol/g and 4.9±0.7 µmol/g, respectively, but also did not change after phosphate deprivation. Replacement of phosphate-deprived hypox rats with GH resulted in a further fall in plasma phosphate and a significant increase in plasma 1,25-(OH)2-D3 levels, but there was no change in either total or acid-soluble renal cortical phosphate content. The distribution of organophosphorus compounds in the acid-soluble phosphate fraction in these experiments was also evaluated using31P NMR spectroscopy. Although there appeared to be an increase in the total concentration of organophosphorus compounds after phosphate deprivation, this effect was not altered by hypophysectomy or by replacement of phosphate-deprived hypox rats with GH. These data suggest that unless phosphate deprivation affects only a small or specific cellular phosphate pool, some factor other than renal cell inorganic phosphate content must initiate the increase in renal 1,25-(OH)2-D3 synthesis that occurs during phosphate deprivation.
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  • 2
    ISSN: 1432-0827
    Keywords: Bone ; Epiphyses ; Calcification ; Physiologic ; Phospholipids ; Phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Neuf polets, âgés de huit semaines, ont reçu 1 mCi de32P orthophosphate par voi intrapéritonéale. Ils ont été sacrifiés 2, 14, 38, 86 et 169 heures asprès injection. Les épiphyses des os longs ont été prélevées et séparés en cartilage au repos, cartilage en voie de prolifération, cartilage en voie de calcification et os spongieux primitif. Les lipides sont extraits: chaque tissu est déminéralisé et les lipides sont extraits à nouveau. On détermine ainsi le contenu en lipides totaux et en phospholipides, ainsi que leurs divers types et l'activité spécifique relative: Le contenu lipidique total de tous les tissus épiphysaires est de 1,35 à 4,52% en poids sec de matrice déminéralisée. La fraction phospholipipidique constitue environ la moitié des lipides. Dans les régions à contenu élevé en calcium, plus de phospholipides sont extraits après déminéralisation qu'avant. Des phospholipides neutres constituten 80–90% des phospholipides totaux dans les extraits réalisés avant déminéralisation, et seulement 48–65% dans les extraits après déminéralisation. La quantité des phospholipides, éthanolamine et sérine, est variable dans les diverses zone épiphysaires. La quantité et les types de phospholipides et leur rapport avec le degré de calcification concordent avec les résultats publiés pour les tissus de veaux. Les courbes d'activité spécifique démontrent une activité réduite au niveau de cartilage au repos et des échange très actifs en phospholipides dans les trois autres zones épiphysaires. Les divers types de phospholipides ont des activités métaboliques nettement différentes les uns par rapport aux autres. Les modes d'échanges particuliers de la phosphatidyle ethanolamine, de la phosphatidyle sérine et de la phosphatidyle inositol, au niveau du cartilage en voie de prolifération et de calcification, suggérent un rôle spécial de ces lipides dans le mécanisme de las croissance et de la calcification.
    Abstract: Zusammenfassung Neun achtwöchige Hühner erhielten intraperitoneal 1 mCi32P-Orthophosphat und wurden 2, 14, 38, 86 und 169 Std nach der Injektion getötet. Die Epiphysen der Röhrenknochen wurden seziert und ruhende, proliferierende und verkalkende Knorpel, sowie primäre Spongiosa voneinander getrennt. Die Lipide jeder Zone wurden extrahiert, jedes Gewebe wurde demineralisiert und die Lipide erneut extrahiert. Der Gehalt der Extrakte an Gesamtlipden und Phospholipiden sowie die Art der Phospholipide wurden bestimmt und die relative spezifische Aktivität: gemessen. Der Gehalt an Gesamtlipiden aller epiphysischen Gewebe betrug 1,35–4,52% des Trockengewichtes der demineralisierten Matrix. Phospholipide machten ungefähr die Hälfte der Gesamtlipide aus. In den Zonen mit hohem Calciumgehalt konnten mehr Phospholipide nach der Demineralisation als vorher extrahiert werden. Die neutralen Phospholipide entsprachen in vor der Demineralisation erhaltenen Extrakten 80–90% und in jenen nach der Demineralisation nur 48–65% der gesamten Phospholipide. Die Aethanolamin- und Serinphospholipidmengen variierten bedeutend in den verschiedenen Zonen der Epiphyse. Die Menge und die Art der Phospholipide und ihr Verhältnis in bezug auf Verkalkungsgrad waren in Einklang mit den Werten, die für das Kalb angegeben werden. Die Kurven der relativen spezifischen Aktivität zeigten ein träges metabolisches Muster im ruhenden Knorpel und einen sehr aktiven Phospholipidumsatz in den drei anderen Zonen der Epiphyse. Die verschieden gearteten Phospholipide zeigten untereinander merklich verschiedene metabolische Muster. Die speziellen Eigenschaften der Umsatzsmuster von Phosphatidyläthanolamin, Phosphatidylserin und Phosphatidylinositol in proliferierendem und verkalkendem Knorpel lassen vermuten, daß diese Lipide spezielle Funktionen im Wachstums- oder Verkalkungsprozeß ausüben.
    Notes: Abstract Nine eight-week old chicks were given32P orthophosphate, 1 mCi, intraperitoneally and killed 2, 14, 38, 86, and 169 hours after injection. Long bone epiphyses were dissected and separated into resting cartilage, proliferating cartilage, calcifying cartilages, and primary spongiosa. Lipids were extracted from each zone, each tissue was demineralized, and lipids were extracted again. The extracts were analyzed for total lipid and phospholipid content, types of phospholipids, and relative specific activity. Total lipid content of all epiphyseal tissues was 1.35 to 4.52% of the dry demineralized matrix weight. Phospholipid was about half the total. In the zones with higher calcium content more phospholipid was extracted after demineralization that before. Neutral phospholipids were 80 to 90% of the total phospholipids in predemineralization extracts and only 48 to 65% in extracts after demineralization. The amount of ethanolamine and serine phospholipids varied considerably in different epiphyseal zones. The amount and types of phospholipid and their relation to degree of calcification corroborated data reported for the calf. Relative specific activity curves revealed a sluggish metabolic pattern in resting cartilage and very active phospholipid turnover in the other three epiphyseal zones. The different types of phospholipids had markedly different metabolic patterns from each other. Special features of the turnover patterns of phosphatidyl ethanolamine, phosphatidyl serine, and phosphatidyl inositol in proliferating and calcifying cartilage suggest special roles of these lipids in the growth or calcification process.
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  • 3
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    Springer
    Calcified tissue international 35 (1983), S. 284-286 
    ISSN: 1432-0827
    Keywords: Phosphorus ; NMR ; Precipitation ; Nucleation ; Phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary High-resolution31P NMR spectroscopy is shown to be a potentially valuable new method for monitoring the spontaneous precipitation of calcium phosphates from metastable supersaturated solutions. An apparatus capable of pH-statting the sample in a spinning 20 mm NMR sample tube is briefly described. The spontaneous precipitation of dicalcium phosphate dihydrate, CaHPO4· 2H2O, pH-statted at pH 5, is characterized by a base-uptake curve which follows the decrease in the intensity of the solution31P resonance. The precipitation of amorphous calcium phosphate at neutral pH, which exhibited an induction period of ∼ 10 min, was also studied. No evidence of NMR peaks from transient clusters or the initial colloidal solid phase has been seen.
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  • 4
    ISSN: 1432-0827
    Keywords: 1,25(OH)2D ; Hypophysectomy ; GH ; T3 ; Phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Hypophysectomy abolishes the four- to fivefold increase in plasma 1,25(OH)2D levels that normally accompanies dietary phosphate deprivation in rats despite a smaller but significant decrease in plasma phosphate in these animals. This effect appears within 1 week of hypophysectomy and may be the result of a lack of GH, T3, or some other pituitary hormone. In hypothyroid rats (2 weeks after TPTX) not given replacement T3, plasma 1,25(OH)2D levels rose threefold from 148±57 pmol/l to 402±96 pmol/l (mean±SD) after 4 days of dietary phosphate deprivation. However, in hypophysectomized animals given replacement T3 alone, plasma 1,25(OH)2D levels rose fourfold from 82±13 to 333±230 pmol/l after 4 days of phosphate deprivation. In addition, in hypophysectomized animals replaced with GH alone, plasma 1,25(OH)2D levels rose from 243±86 to 525±85 pmol/l during phosphate deprivation. These results would suggest that both GH and T3 must be absent to prevent enhanced renal 1,25(OH)2D synthesis during phosphate deprivation. GH and T3 appear to play a permissive role since plasma levels of these hormones do not increase when intact rats are deprived of phosphate. Furthermore, bioassayable somatomedin levels are also not increased in intact rats during phosphate deprivation as well as plasma levels of prolactin. As observed previously, plasma 1,25(OH)2D levels were inversely correlated to plasma phosphate concentrations (r=0.46,P〈0.025), despite the inclusion of data points for unreplaced hypophysectomized animals who were hypophosphatemic but showed no increase in plasma 1,25(OH)2D. Thus the possibility remains that GH and T3 may exert their effect by permitting the renal 25OHD-1α-hydroxylase to respond to a change in phosphate concentrations during dietary phosphate deprivation, that, in turn, may ultimately increase renal 1,25(OH)2D synthesis and plasma levels of this hormone.
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  • 5
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    Cell & tissue research 111 (1970), S. 15-31 
    ISSN: 1432-0878
    Keywords: Subcommissural organ ; Toads ; Apical secretion ; Fine structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The ependymal cells of the toad subcommissural organ produce pale and dense secretory granules. Both types of granules are mainly concentrated in the apical cytoplasm and in the perinuclear region. Pale and dense granules are synthesized by and packed in the rough endoplasmic reticulum, bypassing the step of the Golgi apparatus. The apical cytoplasm of some subcommissural ependymal cells protrudes into the ventricle. All the cells project a few cilia and numerous slender, long microvilli into the ventricular lumen. Contacting the cilia and the microvilli there is a filamentous material identical to that observed in the fibre of Reissner at the aqueduct of Sylvius. In addition to filaments, the fibre of Reissner contains vacuolar formations. The fibre is surrounded by numerous ependymal cilia, some of which are embedded in the filamentous material of the fibre. The presence of numerous microvilli projected into the ventricle and the large number of vesicles scattered in the supranuclear cytoplasm seem to indicate that the subcommissural organ may have absorption functions. The fact that the intercellular space of the ependymal layer of the subcommissural organ is not separated from the ventricular lumen by tight junctions but by zonulae adhaerentes could indicate that the cerebrospinal fluid penetrates these intercellular spaces bathing all sides of the ependymal cells. The presence in the ependymal cells of vesicles opening into the intercellular space would be in agreement with the latter possibility. There are some ultrastructural differences between the ependymal cells of the cephalic end of the subcommissural organ and those of the caudal end. A critical analysis of Reissner's fibre formation is made.
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  • 6
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    Cell & tissue research 107 (1970), S. 421-446 
    ISSN: 1432-0878
    Keywords: Fresh-water and adapted stickleback-gills-chloride sea-water cells ; Fine structure ; Na+ and Cl− localization ; Osmoregulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Dreistachlige Stichlinge (Gasterosteus aculeatus) aus Süßwasserbiotopen wurden in mehreren Versuchsgruppen allmählich an Meersalzlösungen steigender bzw. fallender Konzentration adaptiert. Dabei stellte sich heraus, daß diese euryhaline Fischart Salzkonzentrationen zwischen 1 mg-% und 5,6% tolerieren kann. Der letzte Wert bedeutet das 1,6fache der durchschnittlichen Meerwasserkonzentration. Stichlinge aus verschiedenen salzreichen und salzarmen Adaptationsstufen dienten als Ausgangsmaterial zur elektronenmikroskopischen Untersuchung der Chloridzellen. Die Feinstruktur der Chloridzellen zeigt in Abhängigkeit vom Salzgehalt des Mediums typische Veränderungen. Bei Süßwasserstichlingen ist die apikale Höhle septiert und dadurch die resorptive apikale Zellmembranoberfläche vergrößert. Bei Meerwasserstichlingen scheint das endoplasmatische Reticulum der Chloridzellen vermehrt zu sein; ihr Chondriom nimmt 50% des Cytoplasmavolumens ein, bei den Chloridzellen der Süßwassertiere hingegen nur 20%. Im Bereich letaler Salzarmut und letalen Salzreichtums treten bei den Chloridzellen Strukturschädigungen auf. Durch histochemische Ionenfällung konnte in der Mucoidschicht der apikalen Höhle ein hoher Gehalt an Na+ und Cl− nachgewiesen werden. Die Mucoidschicht dieser Zellen füngiert demnach bei Süßwassertieren als akkumulativer Ionenfänger, bei Meerwassertieren möglicherweise als Ionenpuffer. Die Feinstruktur der Chloridzellen, ihre Veränderungen in Abhängigkeit von dem äußeren Salzgehalt, die Schädigungen bei letalen Konzentrationen sowie insbesondere die Ergebnisse der histochemischen Ionenfällung können insgesamt als Beweis der osmoregulatorischen Funktion dieser Zellen gelten.
    Notes: Summary Several groups of the stickleback (Gasterosteus aculeatus) collected from freshwater were gradually adapted to sea salt solutions of increasing resp. decreasing concentrations. As shown by these adaption experiments, this euryhaline teleost species is able to tolerate salt concentrations in the range of 1mg-% to 5,6%. The last value corresponds to 1,6 times of the average salt concentration of sea water. Specimen adapted to minimum, intermediate and maximum salt concentration were chosen for electron microscopical investigation of the chloride cells. Depending on the external salt concentration the fine structure of these cells shows typical alterations. In fresh water specimen, the apical cavity of the chloride cells is septate and consequently the resorptive apical cell membrane surface is enlarged. In sea water specimens the endoplasmic reticulum seems to be more developed; the mitochondria take about 50% of the cytoplasm volume, whereas they take only 20% in fresh water animals. The chloride cell fine structure of those animals which had been brought to the upper or lower limit of the tolerable salt concentration is damaged. The mucoid layer of the apical cavity in animals from both salt-rich and nearly salt-free medium has a high content of Na+ and Cl−, as detected by histochemical ion precipitation methods. Therefore in fresh water specimens the mucoid layer must be involved in adsorbing and in accumulation ions from the external medium, in sea water specimens its function seems to be something like an ion buffer. From these findings there is no doubt that the osmoregulatory function of the teleost gills is based on the chloride cells.
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  • 7
    ISSN: 1432-0878
    Keywords: Interphase nuclei ; Ultracentrifugation ; Fine structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Ultracentrifugation of living cells from the liver of the mouse, rat, dog, frog, Necturus, follicle cells, of grasshopper testis, and meristem of the onion root tip shows evidence that the interphase chromatin is attached to the nuclear envelope. Because of its relatively high density, the bulk of the interphase chromatin, and often the nucleoli, are displaced to the centrifugal side of the nucleus and, when this occurs, the chromatin bodies attached to the centripetal side of the nucleus are drawn out into long filaments which extend across the nucleus centrifugally. They generally break before becoming detached from the envelope. Onion root tip chromosomes in early prophase also appear to be attached to the nuclear envelope. The Barr body strongly adheres to the nuclear envelope as evidenced by the high centrifugal force necessary to displace it. Nucleoli of ultracentrifuged meristematic cells of the onion root show evidence of a stratification of materials within them.
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  • 8
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    Cell & tissue research 111 (1970), S. 228-262 
    ISSN: 1432-0878
    Keywords: Retina ; Rod outer segment ; Frog ; Freeze-etching ; Fine structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Der Feinbau der Stäbchenaußenglieder des Frosches (Rana esculenta) wurde mit zwei verschiedenen Methoden untersucht: der größte Teil der Untersuchungen wurde mit der Gefrierätzmethode durchgeführt. Die Abdrucke (Masken der Bruchflächen) wurden im Elektronenmikroskop bei 40000facher Vergrößerung betrachtet. Als zweite, von der ersten unabhängigen Methode, wurden Teile negativ kontrastierter Außenglieder des Frosches im Elektronenmikroskop betrachtet. Die Auswertung der elektronenmikroskopischen Aufnahmen von Abdrucken ergab: die Außenglieder des Frosches scheinen aus 3 Gruppen „länglicher Gebilde“ aufgebaut zu sein, die in jeweils angenähert gleichen Abständen angeordnet sind. Die „länglichen Gebilde“ werden als Fäden bezeichnet; ihre Durchmesser liegen unter 100 Å. Die Größe der Durchmesser hängt vom Adaptationszustand und der chemischen Behandlung vor der Gefrierätzung ab. Die Fäden überkreuzen sich z.T. — Es wurden ferner 4 Gruppen angenähert gleicher Abstände zwischen den Fäden gefunden. Die Größe dieser Abstände liegt zwischen etwa 50 Å und einigen hundert Å. Negativ kontrastierte Außenglieder ließen ebenfalls Fäden erkennen. Die Ergebnisse werden zu einer zweiteiligen Arbeitshypothese zusammengefaßt. Im 1. Teil der Arbeitshypothese wird angenommen: der Innenkörper des Außengliedes (das ist das Außenglied ohne die erkennbare Zellmembran) ist ein dreidimensionales parakristallines Raumgitter, aufgebaut aus den 3 verschiedenen dicken Fadenarten (d 1, d2, d4). Die Abstände zwischen den Fäden werden als Gitterkonstanten (a 1, a2, a3, a4) dieses Raumgitters aufgefaßt. Eine Elementarzelle des Gitters scheint aus einem Geflecht aus d 1- und d 2-Fäden zu bestehen und aus vier darüberliegenden Schichten paralleler d 4-Fäden. Im 2. Teil der Arbeitshypothese wird auf Grund von Volumenabschätzungen angenommen: die d 1-Fäden des Raumgitters enthalten Rhodopsin, die d 2-Fäden Protein, das nicht Rhodopsin ist, und die (d 4-Fäden enthalten Lipide. Die Arbeitshypothese wird durch experimentelle Befunde anderer Autoren gestützt, die mit den Methoden der negativen Kontrastierung, der Licht- und Röntgenstrahl-Kleinwinkel-Beugung experimentierten. Es wird versucht, für einige elektronenmikroskopische Aufnahmen von Dünnschnitten und Gefrierätzabdrucken eine gemeinsame Deutung zu geben (Rosenkranz et al., 1969; Rosenkranz, 1969a).
    Notes: Summary The fine structure of the frog's (Rana esculenta) rod outer segments was investigated by two different methods: most of the experiments were made by means of the freeze-etching technique. The replicas were then examined by electron microscopy (40,000 X). By means of a second method, rod outer segments were negatively stained prior to electron microscopy. Inspection of the electron micrographs revealed that the frog's rod outer segments seem to be built up of three groups of “elongated structures” interpreted as fibrils (Fäden) arranged regularly at approximately equal distances. The diameters of the fibrils are below 100 Å; they depend on the state of light adaptation and on the chemical preparation before freeze-etching. The fibrils partly cross each other. In addition, there were found four groups of approximately equal distances between the fibrils. The order of magnitude of these spacings is from about 50 Å to a few hundred Å. Negatively stained outer segments also reveal fibrils. The results are expressed in a working hypothesis consisting of two parts. It is supposed first that the core of the rod outer segment represents a three dimensional paracrystalline lattice (Raumgitter) of three different types of fibrils (d 1, d2, d4). The distances between the fibrils are interpreted as the lattice constants (a 1, a2, a3, a4). A unit cell of the lattice would consist of a web (Geflecht) of two different types of fibrils (d 1, d2) and four layers of parallel fibrils of the third type (d 4). It is supposed, secondly, on the basis of a volume-evaluation, that the d1-fibrils contain rhodopsin, those of type d 2 another protein (not rhodopsin), and fibrils of type d 4 lipids. The working hypothesis is supported by experimental findings of other authors (obtained by negative staining and diffraction of light and X-rays). Attempts have been made to relate some electron micrographs of ultrathin sections to those of replicas. (Rosenkranz et al., 1969; Rosenkranz, 1969a.)
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  • 9
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    Cell & tissue research 110 (1970), S. 204-218 
    ISSN: 1432-0878
    Keywords: Polychaetes ; Parapodia ; Glands ; Fine structure ; Mucus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The spiral organs of Nereis have been shown to be compound glands and not photoreceptors. The ducts of two or three types of secretory cells attach themselves in a serial manner to a spirally wound axial columella which lies just below the cuticle. The large intra-cellular ducts terminate in a number of fine ducts which penetrate the columella and open through it into the lumen of the gland. This communicates to the outside through a pore in the cuticle. The secretions are muco-polysaccharides which are probably mixed in the lumen before discharge.
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  • 10
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    Cell & tissue research 108 (1970), S. 46-58 
    ISSN: 1432-0878
    Keywords: Compound eyes ; Insecta ; Pteronemobius heydeni ; Fine structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Die Ommatidien der Sumpfgrille Pteronemobius wurden elektronenmikroskopisch untersucht. Der dioptrische Apparat besteht aus der cuticularen Linse, auf der zahlreiche Cornea-Nippel stehen, sowie dem Kristallkegel mit seinen Zellen, die auch noch beim adulten Tier Mitochondrien besitzen. Diese vier Zellen bilden insgesamt acht nach basal gerichtete Fortsätze, vier laterale und vier zentrale. Die lateralen, die auch bei anderen Insekten vorkommen, ziehen zwischen den Retinulazellen bis zur Basalmembran, an der sie enden. In ihrem proximalen, erweiterten Bereich nehmen die Fortsätze Kontakt miteinander auf. Hier enthalten sie außer den für den gesamten Verlauf typischen Mikrotubuli Pigment und feine Granula, die denen des Kegels gleichen. Die vier anderen, zentral gelegenen Fortsätze bilden gemeinsam den dünnen Spitzenausläufer der Kegelbasis. Er wird vom Rhabdom umhüllt und endet nach etwa 6 μm. Sieben oder acht Retinulazellen bilden ein Rhabdom vom geschlossenen Typ. Zunächst umfassen vier dieser Zellen den Kegel, doch treten noch vor seinem basalen Ende drei weitere hinzu. Die beiden primären Pigmentzellen werden dabei peripherwärts abgedrängt. Die sekundären Pigmentzellen bilden keinen geschlossenen Zylinder um die Retinulazellen.
    Notes: Summary The ommatidia of the gryllid Pteronemobius have been examined electron microscopically. The dioptric apparatus consists of a cuticular lens on which numeral nipples insert and of the crystalline cone with its cells bearing mitochondria even in the adult. These four cells form altogether eight proximally directed processes, four lateral and four central ones. The lateral processes — as in other insects — extend from between the retinula cells to the basal membrane at which they terminate. In its proximal enlarged region they get into contact with each other. Besides those microtubuli typical for the total process they contain pigment and fine granules similar to those of the cone. The four remaining processes centrally situated form the thin pointed appendix of the cone basis being enveloped by the rhabdom and ending after about 6 μm. Seven or eight retinula cells form a rhabdom of the closed type. Primarily there are four of these cells enclosing the cone, however, farther proximally they are joined by three more cells. Thus, the two primary pigment cells are forced away towards the periphery. The secondary pigment cells do not constitute a closed cylinder around the retinula cells.
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