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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 541 (1988), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Medical electron microscopy 32 (1999), S. 67-78 
    ISSN: 1437-773X
    Keywords: Key words Electron microscopy ; Human yolk sac ; Yolk stalk ; Vitelline duct ; Human embryo ; Human development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Organogenesis occurs during the first 8 weeks of human embryonic development; in consequence, early human growth and development take place before and in the absence of fully developed internal organs. During this period, normal development depends on several factors, but two are imperative: nutrition and a functional transport system for the distribution of nutrients and for waste disposal. The yolk sac (YS), a highly differentiated adnexal organ, is known to accomplish this fundamental task during early pregnancy. In this review, we summarize our contribution to the understanding of early human embryology, focusing interest on analysis of the morphofunctional link that is established between the human embryo and the YS during the embryonic period. Embryos were collected from the gestational sac after salpingectomies performed on patients with singleton pregnancies occurring in the fallopian tube. Samples of YS were taken from 20 human embryos at Carnegie stages ranging from 12 to 20. The age of the embryo was estimated from data of the patient's last menstrual history and confirmed from crown-rump length measurements and morphological characteristics of the specimen. The samples were fixed in 3% glutaraldehyde and then postfixed in 2% osmium tetroxide and prepared for light, transmission, and scanning electron microscopy according to conventional techniques. The samples were examined with a Philips 301 EM and an S-4000 Hitachi field emission SEM. The yolk stalk, and the YS wall with its corresponding endodermal, mesenchymal, and mesothelial layers, were analyzed. In accordance with their morphological features, the endodermal cells are equipped with organelles to fulfill several functions that are expressed in absorption from the vitelline cavity via microvilli present into the outer cell surface, in secretion to the extracellular space, and in the synthesis of numerous proteins which are transported by the bloodstream to the embryo. The mesothelial surface is provided with cell-surface differentiation that promotes a protective coat to prevent damage from compression or friction of the YS wall against the amnios, umbilical cord, and chorionic cavity wall during growth. The mesenchyme is the main site for blood vessel formation and gives rise to a network that provides the embryo with nutrients and a means of waste disposal. A critical analysis of the role of the endodermal vesicle in the production of fluid that is accumulated in the YS, and of the role that the vitelline duct play in the exchange function between the YS and intestinal tract, is presented. We have demonstrated that the vitelline duct is not functional after week 5 because of the closure of its lumen. This finding is discussed with reference to the biological meaning of the vitelline duct and its functional period of activity, and its possible role in the physiology of exchange during the embryonic period is assessed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 145 (1974), S. 223-226 
    ISSN: 1432-0568
    Keywords: Rat ; Liver ; Bile ducts ; Cilia ; Scanning Electron Microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Numerous cilia have been demonstrated by SEM in cells of rat perilobular and portal bile ducts and ductules. Generally these cilia appear as long, cylindrical evaginations of the plasma membrane. Some of them are so long that, curving and twisting at many points, they cross the ductal lumen. It has been suggested that they may be related to a continual mixing up and propulsion of the bile product down the biliary tree.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 176 (1977), S. 493-504 
    ISSN: 1432-0878
    Keywords: Pancreas ; Acinar cells ; Cell surface ; Dissociation ; Scanning electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The pancreatic acinar cell surfaces have been studied by SEM with a dissection technique and correlated with results obtained by TEM. The SEM results demonstrate characteristic arrangement of microplicae which in some areas are densely packed. In many areas, the microplicae are distributed in such a manner that they create zones with typical geometrical shapes and show a relatively smooth surface. These smooth areas may coincide, as indicated by correlated TEM results, with the limits of intimate contact between adjacent acinar cells which, in turn, represent part of the junctional complex. Another aspect revealed by these SEM preparations concerns the presence of groups of densely packed microplicae, arranged in regular rows and distributed along some grooves and/or infoldings of the cellular surface. On the basis of SEM and TEM information, it is likely that these structures correspond to intercellular (and possibly, in some cases, intracellular) canaliculi which topographically form a kind of extensive microlabyrinthine arrangement running along all the cell sides. One final point revealed by fractured samples concerns the finding of spherical zymogen droplets within the vesicles of the Golgi complex. Because in many scanning images these vesicles appear connected by small openings, it is suggested that they may represent a system of intercommunicating chambers (vacuoles) through which the zymogen droplets can be continuously accumulated and discharged into the acinar lumen.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 164 (1975), S. 371-385 
    ISSN: 1432-0878
    Keywords: Kupffer cell ; Endothelial cell ; Sinusoid ; Liver ; Scanning electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The surface ultrastructure of Kupffer cells in the rat liver has been studied by scanning electron microscopy (SEM). The results demonstrate that Kupffer cells are both significantly different and clearly distinct from endothelial cells. Kupffer cells have neither pores (and/or “sieve plates”) nor fenestrations, all of which are present in endothelial cells. They possess a stellate shape, and only indirectly, with slender and irregular evaginations, contribute to the lining of the sinusoidal wall. Furthermore, the luminal surface in some areas contains a large population of short microvilli, microplicae and invaginations. These elements form a kind of microlabyrinth which may correspond to the “worm-like” structures described by transmission electron microscopy (TEM). In the present study, transition forms between endothelial and Kupffer cells were never found. On the contrary, considering the highly fenestrated nature of the endothelial cells, the Kupffer cells may, by ameboid movements, easily cross the overlapping barrier of the sinusoid and protrude into the lumen. Thus, acting as activated macrophages, the Kupffer cells might function to prevent the entrance of foreign material into the tissues of the liver through the fragile and highly fenestrated endothelium. Finally, the topographical reconstruction of the sinusoid by correlated SEM and TEM studies demonstrates that Kupffer cells, with their protruding cytoplasm and ability to extend into the lumen of the sinusoid, may actually change the caliber of the vessel, and thus function as a “sphincter” which causes a temporary arrest of the blood flow when the diameter of the sinusoidal lumen is reduced.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 148 (1974), S. 111-125 
    ISSN: 1432-0878
    Keywords: Liver ; Sinusoids ; Kupffer cells ; Spaces of Disse ; Scanning electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The inner surface of sinusoids and adjacent hepatocytes have been examined by scanning electron microscopy. The endothelial cells lining the sinusoids show large numbers of fenestrations which vary greatly in size and arrangement. Some are very small (0.1 μm) and arranged in clusters; others that are much larger (∼1.0 μm) are subdivided by slender strands of cytoplasm. At sites where the larger fenestrae are present it is evident that the endothelial lining of the sinusoid is double. This may represent a kind of structural assurance against complete breakdown of what seems to be a very thin and fragile endothelial wall. Junctions between adjacent endothelial cells have not been found in these preparations. The open continuity of the sinusoid is occasionally interrupted by slender extensions of cells morphologically distinct from the thin fenestrated endothelial cells. These possess a characteristically textured surface and are thought to represent stellate Kupffer cells. The SEM images describe the subendothelial Spaces of Disse as being larger and as having more extensive ramifications than is generally evident from transmission micrographs. The space, limited on one side by the hepatocyte with numerous microvilli and on the other by endothelial cells, appears actually to be only part of an extensive labyrinth of intercellular channels. These connect the more discrete Spaces of Disse and extend into the narrower spaces between the hepatocytes. The total effect of this system is to expose the greater part of the liver cell surface to the blood filtrate. Microvilli populate the hepatocyte surfaces except for narrow margins which border the bile canaliculi. Whether their presence coincides with the adsorbing surfaces and their absence with secreting surfaces can be decided best by experimental studies.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 163 (1975), S. 29-44 
    ISSN: 1432-0878
    Keywords: Spermatozoa ; Capacitation ; Uterus ; Acrosome Reaction ; Scanning electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The surface morphology of rabbit spermatozoa, fixed in situ (female reproductive tract) and prepared for scanning electron microscopy by critical point drying, was studied for as many as 36 hours post coitum. The findings demonstrate that 1) spermatozoa in the reproductive tract following coitus exist as a heterogenous, morphological population and 2) with time, shifts within this population from one predominant morphology to another take place. In the fresh ejaculate, most spermatozoa have intact surfaces free of membranous disruptions. With time, a process of labilization (denudation) of the membranes covering the acrosomal region occurs in a progressively larger proportion of spermatozoa. The labilization originates by a process of vesiculation and/or vacuolation and leads to the appearance of a series of small fenestrations or perforations of the surface membranes. The perforations coalesce, and gradually larger areas of the surface membranes are eroded such that by 15 hours post coitum, the outer acrosomal membrane, as well as other acrosomal areas, are to varying degrees, directly exposed to the uterine milieu. Secretory granules, picked up by cilia and transferred to the spermatozoa become localized over the acrosomal region shortly after coitus. The possible significance of these time-dependent, morphological events with the phenomena of capacitation and the “true” and “false” acrosome reactions are discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 189 (1978), S. 131-153 
    ISSN: 1432-0878
    Keywords: Luteo-follicular complex (rodents) ; Formation of corpus luteum ; Repair of the ovulated follicle ; Regression of corpora lutea ; Scanning EM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary As observed by SEM, the repair of an ovulated mammalian follicle is accompanied by a sequence of morphogenetic processes. In the initial phase, a mass of cells and coagulated fluids forms at the site of rupture. Shortly thereafter, connective cells, recruited from the adjacent and subjacent connective tissue stroma begin to proliferate and to migrate over this mass such that in the rabbit, the entire site of disruption is covered by a layer of connective cells by approximately 2 days following ovulation. Coincident with the migration of the connective tissue, superficial cells from undisturbed lateral and basal areas of an ovulated follicle also proliferate and begin to migrate over the newly established connective tissue matrix. By approximately 4 days following ovulation in the rabbit, the surface of an ovulated follicle is repopulated by elements of the superficial epithelium. The formation of the underlying corpus luteum (corpora luted) involves characteristic morphological changes as granulosa cells transform into steroid secreting luteal cells. The luteal cells become organized into cords of cells which usually surround capillary vessels. When examined by SEM, the smooth-surfaced endoplasmic reticulum of the luteal cell is quite apparent and is observed to form a three-dimension network of anastomosing tubules which are continuous with the nuclear membrane. Variations in the appearance of the surface of the ovary which directly overlies corpora lutea were observed when the mouse, rat and rabbit were compared. The regression of corpora lutea involves the infiltration of the luteal mass by connective tissue and both degeneration and vacuolization of the luteal cells. The regressing corpus luteum is a honey-comb-like structure in which each space is occupied by a degenerating luteal cell.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 240 (1985), S. 519-528 
    ISSN: 1432-0878
    Keywords: Polycystic mouse ovaries ; Hormone treatment ; Morphometry ; Gap junctions ; Ovary
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Morphological alterations induced by dehydroepiandrosterone (DHA) were studied in polycystic mouse ovaries (PCO). Treated mice showed ovulatory failure and cystic changes; cysts and follicles in various stages of growth and atresia were present although corpora lutea were absent. The levels of testosterone, dihydrotestosterone, 3α- and 3β-androstanediol, estrone and androstenedione increased, whereas estradiol was not detectable. The ultrastructure of granulosa cells in healthy and atretic follicles was similar to that of control animals, although the membrana granulosa in cysts was reduced to a monolayer of flattened cells. The theca interna of healthy and atretic follicles and ovarian cysts showed ultrastructural signs of abnormal steroidogenic stimulation. No significant differences (0.7〈P〈0.8) were found between the extensive surface area of gap junctions of healthy follicles of control and DHA-treated animals. On the P-face of granulosa cells of large healthy follicles, meandering strands of tight junctional particles were observed; their average length was significantly longer than those in healthy follicles of control animals (P〈0.001). This increase was probably related to the large amounts of androgens present in the treated animals. Theca interna cells possessed small gap junctions; no significant differences (P〉0.9) in gap-junction surface area were observed between DHA-treated and control animals. These results suggest that the size of gap junctions is probably unrelated to the steroidogenic activities of theca cells.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 68 (1965), S. 308-319 
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Résumé On a effectué une étude ultrastructurale sur les ≪corps de Call et d'Exner≫. Ceux-ci se montrent constitués, sous leur aspect le plus typique, par une couronne de cellules de la granulosa disposées autour d'une cavité pleine d'un liquide semblable au ≪liquor folliculi ≫. Les cellules, de forme irrégulière, accolées dans leur partie proche du ≪corps≫ et écartées dans celle éloignée, déterminent des fentes dans lesquelles s'insinuent des groupes d'autres cellules voisines; la membrane cytoplasmique, parfois présente sous forme de microvilloités, parfois incisée, montre de fréquentes interruptions; le cytoplasme riche en ribosomes libres et adhérant aux parois du réticule endoplasmique (ergastoplasme), possède en outre un appareil de Golgi modérément développé et de nombreuses mitochondries; le noyau, très volumineux, présente à l'intérieur un nucléole grossièrement réticulé. Le ≪corps de Call et d'Exner≫ proprement dit est, au contraire, constitué par une cavité unitaire d'aspect à peu près sphérique d'environ μ 15–30 de diamètre, pleine d'un liquide dont les caractéristiques sont comparables à celles du ≪liquor folliculi≫; dans cette cavité on voit un fin réseau à mailles irrégulières, tandis que sa surface montre une mince zone de ≪condensation≫. L'aspect ultrastructural des cellules disposées autour des ≪corps de Call et d'Exner≫ est caractérisé par des cellules en élaboration, ce qui laisse penser qu'une partie de cette élaboration peut être versée à l'intérieur du ≪corps≫, en contribuant ainsi à l'augmentation de son volume. En ce qui concerne, enfin, le réticule que l'on voit à l'intérieur du ≪corps≫ il est vraisemblable qu'il soit du à des phénomènes de condensation et consécutif à un état physicochimique particulier du liquide endocavitaire.
    Notes: Summary The so-called “Call-Exner bodies” have been found to be formed, in their most typical shape, by a ring of granulosa cells enclosing a cavity filled with a fluid comparable to the liquor folliculi. The cells, irregular in shape, lying side by side in their portions closer to the “body” and far apart in their distal portions leave open spaces which are occupied by prolongations of adjacent cells. The cytoplasmic membrane, sometimes forming mierovilli, sometimes incisions, presents a discontinuous aspect; the cytoplasm is very rich in ribosomes which can be free or sticking to the walls of the endoplasmic reticulum (ergastoplasm). It has a fairly developed Golgi's apparatus and numerous mitochondria, sometimes open. The very voluminous nucleus shows internally a roughly reticulated nucleolus. The “Call-Exner body”, on the other hand, is a unitary cavity approximately spherical in shape, having about a 15–30 micron diameter filled with a fluid characteristically similar to the liquor folliculi, which shows internally a fine reticulation of irregular meshwork, while a thin “condensation zone” can bee seen peripherically. The ultrastructural aspect of the cells radiating from the Call-Exner bodies is typical of cells in formation. Therefore we cannot exclude the possibility that a portion of the substances elaborated by the cells may be thrown into the center of the “body”, thus contributing to its increase in volume. The mesh-like structure visible inside the “body” may be due to condensation phenomena following a particular physico-chemichal change in the endocavitary luid.
    Type of Medium: Electronic Resource
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