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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Antidiuretic hormone (ADH) promotes fusion of cytoplasmic tubules with the luminal membrane and delivery of particles from the tubules to the membrane. The particles are believed to be the water-conducting elements in the membrane. We have employed several scanning (SEM) and transmission electron-microscopic (TEM) techniques to study the relationship of the cytoplasmic tubules to the luminal membrane and to the apical cytoskeleton of the toad bladder epithelial cell. This paper reports the results of freeze-crack SEM and tannic acid-fixed TEM studies, as well as studies with a resinless method of embedding. Freeze-cracked epithelial cells reveal that the tubules are anchored in a matrix of cytoskeleton and granules just below the luminal membrane, and many, if not all, retain their anchorage to the matrix after ADH-induced fusion. Tannic acid-fixed specimens show that the tubules in unstimulated cells lie horizontally. Fusion appears to involve an angulation of the tubules, and this may be the major mode of ADH-induced tubule movement. There are suggestions in the tannic acid sections of filamentous attachments of tubules to the surrounding cytoskeleton. In addition there are prominent microfilament bundles running down the microvilli and a dense concentration of filaments just below the luminal membrane. The presence of these filaments is confirmed in the resinless sections, and their possible role in ADH action is discussed.
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PMID:Electron-microscopic study of the apical region of the toad bladder epithelial cell. 643 17

Low grade infections following total hip replacements manifest themselves late after surgery. These infections seem to be sterile; there are major problems in identifying the causative organism by cultivation. SEM investigation of small samples of the bone cement, the task of which is to anchor the prosthesis in the bone, is a suitable method for identifying the bacterial origin of these infections. During conventional histological preparation polymethacrylates are dissolved. Freeze-drying techniques, however, allow the preparation of bone cement samples for the SEM. The growth of staphylococci on cement particles shows that these resins can no longer be considered biologically inert. The surface is attacked by the bacteria.
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PMID:Adherence and growth of bacteria on bone cement in vitro and in chronologically infected artificial joints. 663 52

The ultrastructure of the proximal tubule of mature mesonephric nephrons was studied in perfusion-fixed pig embryos of the 41st gestational day. Despite its 8-12 mm long course, the proximal tubule possesses no cytologically different subsegments except its very last cells at the abrupt transition into the distal tubule. The first brush-bordered proximal tubule cells stand considerably within Bowman's capsule, abuting its attenuated cells. In SEM specimens, the average luminal cell diameters are 8 X 13 micron. The cells are 6-11 micron in height with overlying microvilli 2-4 micron long. Lateral faces of perfectly disjoined cells exhibit plate-like interdigitating processes projecting more than 5 micron deep into the neighboring cells. The basal cell face is completely covered with microvilli. The TEM pictures reveal an endocytic apparatus largely matching its metanephric counterpart. Mitochondria account for 23% of the cytoplasm and together with the many basolateral cell membranes indicate a high capacity for energy-dependent transport processes. Small basal lipid droplets represent a species peculiarity. Freeze-fracture specimens show an electrocoupling of the cells by gap junctions. The tight junction, with only 1-2 strands, characterizes a "leaky" epithelium. In most features, this tissue is as mature as its metanephric counterpart.
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PMID:The pig mesonephros. II. The proximal tubule: SEM, TEM and freeze-fracture images. 666 May 64

The objective of this study was to characterize complement-dependent damage to the tegument of isolated metacestodes of Taenia taeniaeformis caused by exposure to immune or normal rat serum (IRS and NRS, respectively). Metacestodes of T. taeniaeformis (34- and 69-day-old) from rats were incubated for 1 hr in 0.85% physiological saline solution (PSS), IRS, NRS, heat-inactivated at 56 C for 1 hr (delta) IRS, or delta NRS and then fixed for 2 hr in 3% glutaraldehyde. The larvae were then prepared for freeze-etching, thin sectioning, and SEM by standard techniques. Freeze-etch replicas of PSS-, delta IRS-, and delta NRS-treated larvae showed no damage, whereas those of IRS- and NRS-treated metacestodes exhibited vesiculation in the extracellular matrices, segmentation or "beading" of the microthrix tip, significant reductions in the number of intramembranous particles (IMP) in the P face of the membrane of the microthrix base, and changes in the pattern of IMP distribution in the P face of the base. Similar results were obtained from larvae prepared for thin sectioning and SEM. Additionally, thin-sectioned preparations demonstrated that in some cases the entire tegument was stripped away in IRS- and NRS-treated metacestodes. Our results have provided supportive evidence that complement-mediated lysis of larvae of T. taeniaeformis is not enhanced by the presence of antibody in serum, and we also characterized ultrastructurally the types of tegumental damage that may contribute to lysis. In addition, a possible defense mechanism used by the parasite to counter immunological attack by host phagocytic cells is proposed.
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PMID:Ultrastructural characterization of serum-induced changes in the tegument of Taenia taeniaeformis. 667 63

Freeze-substitution is a technique suitable for the preparation of unicellular and multi-cellular plant and animal specimens for conventional light microscopy, TEM and SEM. It is also widely used as a means of preparing animal and plant tissues for the localization of water soluble substances by analytical electron microscopy, autoradiography or visual detection of precipitates. The technical requirements of preparation, together with an evaluation of the procedures, are presented for various applications. Careful selection and evaluation of freezing technique, substitution solvent and regime are required for meaningful results.
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PMID:Freeze-substitution. 675 Jan 31

The aim of preparing specimens at very low temperatures is to maintain biological tissue in its natural state. The problems which arise are: 1) obtaining the highest possible cooling rate when freezing the tissue; 2) preventing melting with recrystallization during the drying process; and 3) preventing the dried specimens from water vapor contamination. Biological tissue is prepared in a cooling chain by freezing the samples in a supercooled nitrogen bath, breaking the specimens in the frozen state, sputtering the fracture surfaces in a vacuum on the cooling stage of a special device and then transferring the specimens under vacuum to the SEM where they are studied on a cooling stage. They have smooth surfaces, with the liquid and solid phases present simultaneously, and no artefacts. Any shifts or deformations which may occur within the structure cannot yet be determined. Freeze-drying quenched specimens at various temperatures (-140 degrees to -60 degrees C) taking the dynamics of vapor pressure into consideration shows that sublimation, the melting processes with recrystallization and the resulting damage to the structures occur simultaneously during the drying process. The destruction of the tissue is inversely proportional to the ratio of sublimation to melting.
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PMID:Ice crystal damage in freeze-dried articular cartilage studied by scanning electron microscopy. 718 52

Evaporative coatings of platinum-carbon and gold on freeze-fractured mouse lung, preserved in frozen-hydrated and freeze-dried states, are studied in secondary emission mode by low temperature scanning electron microscopy. Unfixed, inflated frozen lung is freeze-etched in high vacuum, metal coated and observed frozen-hydrated and freeze-dried, to demonstrate sample shrinkage and coating deformation upon drying the sample. Buckling and cracking of the coatings occur as a result of freeze-drying. Correlative TEM thin film analysis of the coatings is used to estimate film thickness and reticularity. Freeze-drying biological samples is a common SEM preparative technique which causes morphological artifacts due to both freezing and drying. Frozen-hydrated low temperature-SEM investigation can selectively study these artifacts morphologically to distinguish between freezing and drying artifacts.
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PMID:Conductive coatings studied on inflated lung in the frozen-hydrated and freeze-dried states. 725 8

We have previously reported details of the dimensional changes taking place during the processing of soft tissue specimens for scanning electron microscopy. Mouse embryo limbs were used for many of these measurements and the present paper deals with the associated morphological findings. Effects of fixation, dehydration and drying are considered. Freeze drying and critical point drying of glutaraldehyde and glutaraldehyde and osmium fixed samples give perfectly acceptable results for scanning electron microscopy. The best volume retention with freeze dried material is matched by the best morphological appearance of the specimen surface, except when ice crystal damage occurs due to a failure to freeze the tissue rapidly enough. For CPD tissues, perforation of the plasmalemma may occur in glutaraldehyde-only fixed tissue, this being prevented by post-osmication if the glutaraldehyde fixation is not unduly prolonged. This perforation may be due to the extraction of some plasmalemma component during dehydration or further solvent substitution on critical point drying. Solvent evaporation drying usually causes recognizable distortion due to shrinkage: this is minimal in the case of solvent evaporation drying in a nearly saturated atmosphere of the same solvent if this is a very volatile solvent. The examples of Freon 113 and diethyl ether are given here. Swelling during early stages of ethanol dehydration can be prevented by using 70% or 100% ethanol as the first step, with marginal reduction in the post CPD volume and no apparent differences in the SEM. The severe swelling causing sample disruption which can occur with GA + OsO4 fixed tissue can also be prevented by treating the sample with divalent cations, such as Ca++ or Cu++, at any stage.
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PMID:Morphological correlations with dimensional change during SEM specimen preparation. 734 23

Parenchymal and stromal components of the rat parotid and submandibular glands were examined by conventional and high resolution scanning electron microscopy (HRSEM). Freeze-fractured specimens were subjected to HCl and NaOH extraction procedures to better differentiate connective tissue and cellular components. In addition, the internal three-dimensional morphology of the secretory acinar cells and duct cells was revealed by maceration with a dilute osmium tetroxide solution to selectively remove some of the cytoplasmic components. SEM and HRSEM examination of the HCl-treated samples of both glands revealed a fine filamentous network immediately surrounding each acinus. Coarser bundles of collagen that linked neighboring acini were also observed. NaOH-extracted samples selectively removed the cellular components and showed more clearly the three-dimensional structure of the connective-tissue stroma. A dense-collagenous network surrounded each lobule while more internal regions consisted of a honeycomb-like pattern of evacuated spaces previously occupied by secretory acini. These spaces were smoothened in appearance and often interconnected. Apically-located secretory granules and profiles of the rough endoplasmic reticulum and Golgi apparatus in perinuclear regions were encountered in the acinar and duct cells of macerated samples by HRSEM. In addition, a phenylephrine-induced experimental condition performed in some rats resulted in a significant increase in secretory granule size and density of the serous cells.
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PMID:Fine structure of the acinar and duct cell components in the parotid and submandibular salivary glands of the rat: a TEM, SEM, and HRSEM study. 872 Apr 53

Native, unfixed collagen fibrils from rat tail tendon were dehydrated following different procedures and observed under a FEG-SEM and an AFM operated in Tapping Mode (TMAFM). Freeze-etched, untreated fibrils from the same tissue were also observed for comparison. The most notable features of the fibril surface, i.e., the gap/overlap alternation and three prominent intraperiod ridges, were simultaneously visible only in freeze-etched specimens, while under the SEM and the TMAFM their appearance was dependent on both the dehydration procedure and the visualization technique. The different susceptibility of the collagen fibril surface structures to various treatments clearly implies the existence of domains of different composition. Moreover, identical specimens were imaged differently by SEM and TMAFM, highlighting instrument-specific advantages and limitations. The onset of dehydration-dependent, procedure-specific artifacts should be considered in high-resolution studies of connective tissues. As for any biological specimen, the final aspect of collagen fibrils is determined no less by the preliminary treatments than by the visualization approach.
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PMID:Collagen fibril surface: TMAFM, FEG-SEM and freeze-etching observations. 887 62


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