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  • Articles  (38)
  • Engineering General  (16)
  • Ultrastructure  (12)
  • Chemical Engineering  (10)
  • 1990-1994  (20)
  • 1975-1979  (18)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 171 (1976), S. 305-315 
    ISSN: 1432-0878
    Keywords: Chorioallantoic placenta ; Gap junctions ; Diaplacental transport ; Ultrastructure ; Freeze-fracturing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Gap junctions were found to be a constant feature of chorioallantoic placentae with two or three trophoblastic layers. The gap junctions connect layers I and II in hemodichorial and layers II and III in hemotrichorial placentae. Although the gap junctions vary in form and in the packing density of membrane-associated particles, they cover an extensive surface area in all species examined. The gap junctions always connect adjacent membranes of two trophoblastic layers, which show no evidence of micropinocytotic activity; at least one of these trophoblastic layers is syncytial. It is therefore concluded that the gap junctions play an important role in diaplacental transport. We consider that gap junctions act as molecular sieves, resulting in limitations in the transport of large molecules. The passage of small molecules, on the contrary, would be facilitated by the gap junctions.
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  • 2
    ISSN: 1432-0878
    Keywords: Liver ; Bile duct ligation (rat) ; Cell membrane ; Intercellular junctions ; Ultrastructure ; Freeze-fracturing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of bile duct ligation on the intercellular junctions of hepatocytes was investigated. The features and the arrangement of the bile canaliculi and the zonulae occludentes alter concomitant to the increase of the intracanalicular pressure. The lumen of the bile canaliculi enlarges and the microvilli disappear. The array of the zonulae occludentes becomes irregularly shaped, the number of strands diminishes and interruptions of the strands occur. With peroxidase a leakage in the bile-blood barrier is detected. Furthermore a disappearance of gap junctions between the hepatocytes after bile duct ligation is observed. The present investigation shows that the zonulae occludentes are mobile structures which are changed by increased unilateral pressure. Due to their ultrastructural alterations, a leakage of the permeability barrier between physiological compartments is found. We acknowledge the helpful criticism and discussion of Prof. H.D. Fahimi. We are indebted to Mrs. B. Brühl, M. Bürkle and Ch. Walenta for technical assistance, and to stud. med. Jon Greenberg for preparing the manuscript
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 172 (1976), S. 431-446 
    ISSN: 1432-0878
    Keywords: Kidney ; Bowman's capsule ; Zonulae occludentes ; Gap junctions ; Freeze-fracturing ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The intercellular connections between the epithelial cells of Bowman's capsule were investigated. It could be demonstrated that typical zonulae occludentes (tight junctions) are present in the species (rat, hamster, and Tupaia) studied. Freeze-fracturing shows a network of anastomizing strands; some species variations are described. In the rat two strands are common. In the golden hamster mostly two to four and occasionally five strands occur. In Tupaia regularly three tight junction strands are found and also gap junctions associated with the zonulae occludentes. In thin sections the goniometric analysis confirms the freeze-fracturing results and reveals attachment zones of macular shape, which are classified as intermediate junctions and desmosomes. The functional role of these cell junctions observed in the epithelium of Bowman's capsule is discussed.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 173 (1976), S. 221-235 
    ISSN: 1432-0878
    Keywords: Exocrine pancreas ; Secretion process ; In vitro experiments ; Ultrastructure ; Parachlorophenylalanine ; Protein synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The in vitro formation of paracrystalline structures after addition of high concentrations of amino acids to the incubation medium was investigated in pancreatic lobules and pancreatic homogenates. It could be shown that even in the homogenate, pCPA induced the formation of paracrystalline structures which exhibited the same ultrastructural arrangement as seen in the in vivo induced paracrystalline inclusions in the RER of the rat pancreas. In correlation with the morphological alterations, the functional consequences to the secretory process, i.e. amylase discharge, discharge of pulse-labeled proteins and incorporation of 3H-leucine into pancreatic proteins, were studied in pancreatic lobules. Two different approaches were used. Firstly, the effect of pCPA-pretreatment of rats and secondly, the effect of higher pCPA concentrations in the incubation medium on the secretory process in untreated pancreatic lobules were studied. A nonparallelism of inhibition of the three different steps of the secretory process depending, with respect to its extent, on time after pCPA-application (4–72 h) and on the concentration of pCPA (1 · 10-5 to 1 · 10-2 M) in the incubation medium was found. In addition to specific effects probably due to pCPA and to the paracrystalline inclusions, unspecific alterations, particularly accompanying degenerative processes after in vivo pretreatment, could be differentiated.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 186 (1978), S. 227-240 
    ISSN: 1432-0878
    Keywords: Pancreas (rat) ; Pancreatic duct ligation ; Cell membrane ; Intercellular junctions ; Ultrastructure ; Freeze fracture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Exocrine pancreatic tissue was investigated during various intervals after pancreatic duct ligation. Concomitant to the increase of the intraluminal pressure, alterations are found in the arrangement of the luminal membrane surface and the zonulae occludentes of the acinar cells. The zonulae occludentes exhibit a disarrangement of their strands. The number of strands diminishes and small interruptions as well as large discontinuities of the strands are observed in most regions of the acinar cells. Furthermore, gap junctions are found very infrequently between acinar cells. The ultrastructural alterations of the zonulae occludentes suggest a gradual adaptation to the increasing unilateral pressure. However, a leakage of the paracellular permeability barrier occurs which contributes to the known shunt between the compartments of the pancreatic juice and the interstitial space following pancreatic duct obstruction. The present investigation is a further example of alterations in the paracellular permeability and intercellular communication of epithelial cells under pathological conditions.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 192 (1978), S. 391-407 
    ISSN: 1432-0878
    Keywords: Placenta (rat) ; Permeability ; Tracer ; Intercellular junctions ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The distribution of lanthanum chloride and horseradish peroxidase within the full-term chorioallantoic placenta of the rat was investigated 1 to 20 min after administration of these tracers into the maternal blood circulation. Both tracers rapidly penetrate trophoblastic layer I and diffuse into the interspace between layers I and II. They are localized in extensive infoldings and caveolae of the outer surface of layer II. The syncytial character of layer II is confirmed at this developmental stage of the placenta. There is no vesicular uptake or penetration beyond layer II until 20 min after tracer administration. Our results indicate that trophoblastic layer II is the main barrier in the chorioallantoic rat placenta preventing the permeation of macromolecules from maternal to fetal compartments. With freeze-fracturing, particulate structures of variable arrangement and size are found between adjacent cells of layer I. With goniometric analysis small gaps between the appositions of the membrane are observed. These structures are interpreted as tight and/or gap junctions during stages of assembly or disassembly.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 192 (1978), S. 409-422 
    ISSN: 1432-0878
    Keywords: Placenta (rat) ; Capillary ; Permeability ; Tracer ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The distribution of horseradish peroxidase and lanthanum chloride within the full term chorioallantoic placenta of the rat was examined after administration of these tracers into the umbilical artery. Both tracers rapidly traverse the capillary endothelium. Transendothelial channels, fenestrations and micropinocytotic vesicles provide the main pathways. Intercellular clefts which are either patent or interrupted by leaky intercellular junctions, also contribute to a rapid passage of low and high molecular weight substances. Deep channel-like invaginations, effecting an increase of the exchange area of layer III, are freely accessible to the tracers from the interspace between the capillary endothelium and trophoblastic layer III. The invaginations, however, are not in continuity with the interspace between layers II and III, verifying the syncytial character of layer III. Neither an uptake of the tracers nor a passage across layer III is observed. The main permeability barrier to feto-maternal transfer within the chorioallantoic placenta is localized in the syncytiotrophoblastic layer III. This layer controls the passage of low molecular weight substances and restricts the penetration of high molecular weight substances.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 260 (1990), S. 469-477 
    ISSN: 1432-0878
    Keywords: Testis ; Interstitial tissue ; Leydig cells ; Lymphatics ; Ultrastructure ; Spinifex hopping mouse ; Notomys alexis (Rodentia)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The organization of testicular interstitial tissue of the spinifex hopping mouse, Notomys alexis differs from that of other rodents. It comprises between 10.3% and 17.3% (average 15.0%) of the total testicular volume, and is variable in its organization both at different locations within the testis of the one animal and among different individuals. Abundant, closely packed Leydig cells are usually present; however, in some regions large, thick-walled blood vessels and extensive peritubular lymphatic spaces, often lacking an endothelium adjacent to the Leydig cells, are also prominent. The Leydig cells in contact with the large blood vessels and lymphatics, unlike those in regions where lymph is sparse, are not densely packed and sometimes contain numerous lipid droplets. Ultrastructure of Leydig cells is typical of steroid-producing cells; however, mitochondria are often extremely large, unusual in shape or bizarely arranged in relation to one another. Also electrondense bodies displaying a paracrystalline-like internal structure of parallel, electron-dense filaments arranged in a lattice pattern occur in the cytoplasm of many cells. The significance of these unusual ultrastructural features and the organization of the interstitial tissue remain to be determined conclusively, but may relate to steroid synthesis, secretion and uptake.
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 13 (1978), S. 17-33 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The fluid forces acting on a uniform cylinder with an infinitely long axis, heaving in the free surface or an infinite ideal fluid, are described in terms of its ‘added mass’ and ‘damping coefficient’. The techniques of multipole expansion and multiparameter conformal transformation are adopted for such calculations and applied to shapes which cannot be adequately represented by the conventional, and more rudimentary, ‘Lewis form fit’. The shapes referred to are both relevant to ship bows, one being a ‘fine section’ and the other a ‘bulbous section’. The parameters which influence the accuracy of the solution are examined. Results for these two sections are computed and compared with results based on (a) the ‘Lewis form approximation’ and (b) the ‘Frank's close fit method’ which employs a singularity representation.
    Additional Material: 8 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 14 (1979), S. 665-679 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A study of the application of the Finite Element Method to compressible potential flows, typified by the airfoil problem, is undertaken. Some novel approaches, believed to simplify solution techniques, are presented.The solutions use two pseudo-variational integrals, appropriate to subsonic flows, and possessing a physical iterative basis. With constant-derivatives triangular elements formulated for cylindrical co-ordinates, accurate solutions are easily obtained for the flow over a circular cylinder. For arbitrary airfoils a simple mapping is used to transform them into near circles. An appropriate mesh is then constructed in the mapped plane. The paper then presents two solution approaches by which this non-linear problem is solved in both the near circle plane and the airfoil plane.
    Additional Material: 9 Ill.
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