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Collagen in bulk was isolated in about 30% yield from the livers of normal human beings and from livers of persons with alcholic cirrhosis. Analyzed chemically and examined by electron microscopy, the collagen in each case was shown to consist of two types identical with, or resembling closely, type I and type III collagens of skin. The collagen from normal liver was predominantly type I, whereas, that from cirrhotic livers consisted or approximately equal amounts of the two types. By chromatography on carboxymethyl-cellulose, the type I collagen from the cirrhotic livers showed one alpha2chain and two alpha1 chains. The alpha1 chains were separable from one another, but gel electrophoretic patterns of peptides obtained from them after treatment with CNBr were almost identical, and resembled the pattern obtained with CNBr peptides of the alpha1 chain of rat skin type I collagen. The increased collagen of both types was responsible in part for the observed distortion of the architecture of the cirrhotic livers associated with increased rigidity of the stroma. The predominance of type III collagen in the areas of collapse of architecture where, as shown by others, few fibroblasts are present, suggests that hepatocytes might have an important function in fibrogenesis during the course of liver cirrhosis.
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PMID:Increase in type I and type III collagens in human alcoholic liver cirrhosis. 106 Nov 56

The high resolution imaging capabilities of modern field emission scanning electron microscopes require adequately improved tissue preparation procedures to prevent the collapse of macromolecular structures and the extraction of molecules. A routine cryo-stabilization technique is described which utilizes chemical crosslinking and cryo-dehydration for mechanical and chemical stabilization of protein and lipid structures and increase of electrical conductivity of the sample. Thiocarbohydrazide (TCH) serves as a general mordant for osmium tetroxide crosslinking. However, extensive washing after all impregnation steps is necessary to dissolve unspecific osmium black precipitations at the sample surface. Collagen I aggregates showed increased stability against collapse after TCH osmification alone, whereas pulmonary surfactant liposomes require additional freeze-substitution in methanol and Freon 113 for stabilization during critical point drying. Environmental scanning electron microscopy (at water vapor pressures of 5-10 torr within the specimen chamber) was used to control, in the wet phase, the stabilization procedure at the level of chemical crosslinkage. It could be confirmed that tannic acid, often used to stabilize lipids, leads to artificial rearrangement of bilayered liposomes into compact presumable multilayered bodies, whereas the TCH osmification preserved liposome structures and their aggregates. The increase of electrical conductivity of sliced tissue was demonstrated on kidney. Support technologies for the cryo-stabilization procedures are described in detail, as well as simple routines for first stabilization trials with new samples. On pulmonary tissue, the excellent preservation of alveolar shape and fine structures of intermediate forms of surfactant are described.
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PMID:Freeze-substitution of chemically stabilized samples for biological field emission scanning electron microscopy. 150 48

Crude papain was administered intravenously to young rabbits and the cartilage of the collapsed ear was examined electron-microscopically. Degeneration and recovery of chondrocytes, and decrease in and recovery of the electron-density of elastic fibers, were observed during the collapse and restoration of the ear. Some samples were stained with ruthenium red. In the collapsed ear, with a marked decrease of proteoglycan in the cartilage, loss of ruthenium red-positive granules was observed in the extracellular matrix. Collagen fibrils in the cartilage appeared to be somewhat increased in number, some of their diameters became slightly greater, and a part were assembled into bundles, occasionally accompanied by periodic cross-striation. Decrease of proteoglycan in the cartilage matrix probably brought about the unmasking and the assembly of collagen fibrils. In one of the experimental animals, collagen fibrous segments of an atypical fibrous long spacing (FLS-)type with symmetrical cross-striation were found around the chondrocytes in the ear cartilage, during the period of recovery. Some kind of the endogenous sulfated carbohydrate may have acted to affect the arrangement of type II collagen or procollagen molecules newly produced by the recovering chondrocytes.
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PMID:An ultrastructural study on the ear cartilage of rabbits after the administration of papain. Appearance of cross-striated collagen segments of an atypical FLS-type. 722 66

Morphologic changes in the subendocardial myocardium that appeared to be caused by severe, chronic subendocardial ischemia were studied in patients with fatal ischemic heart disease admitted to the Specialized Center of Research for Ischemic Heart Disease at the University of Alabama in Birmingham in the period 1970--1977. Thirteen patients were selected for this report on the basis that they had the lesions in the subendocardial myocardium we believe to have been caused by subendocardial ischemia and had no evidence of acute or remote myocardial infarction or other conditions that may have contributed to their terminal illness or death. Clinical findings were unstable angina, congestive heart failure, usually no increase in plasma enzymes indicative of myocardial damage, and electrocardiographic changes consistent with subendocardial ischemia. All 13 patients had 75% or greater stenosis of the three major coronary arteries; none had acute thrombotic or embolic coronary artery occlusion. The left ventricle in all cases was hypertrophied. The subendocardial myocardium showed circumferential pallor, hyperemia, or focal fibrosis without perceptible loss of volume in papillary muscles or trabeculae carneae. Microscopically, acute lesions showed one to two layers of preserved myofibers adjacent to the endocardium, vacuolar change in the deeper fibers, and focal areas of coagulation necrosis of variable size in the myocardium external to the fibers with vacuolar change. Coagulation necrosis was extensive in some cases and usually was not associated with infiltration of neutrophils. The repair reaction involved removal of necrotic sarcoplasm by mononuclear phagocytes, resulting in a reticular-appearing tissue without evidence of stromal collapse. Granulation tissue was not seen. Collagen fibers appeared to be deposited within the area of previous sarcolemmal sheaths. The distribution and morphology of subendocardial myocardial lesions associated with severe coronary atherosclerosis are distinctive and can be distinguished from myocardial necrosis or fibrosis associated with acute total occlusion of a coronary artery.
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PMID:Subendocardial ischemic myocardial lesions associated with severe coronary atherosclerosis. 736 50

Renal tubulointerstitial fibrosis may result from a loss of tubulointerstitial volume, which produces a disproportionate increase in the density of matrix. This study examines the relationship between fibrogenesis and collapse in scar formation after experimental renal infection. Escherichia coli were inoculated into the renal cortex of Sprague Dawley rats, with saline substituted in a control group. Glomerular, tubular, and interstitial profile areas were determined. Density of glomerular profiles was used as a measure of tubulointerstitial collapse. Collagen type I, III, and IV expression was examined by in situ hybridization and immunohistochemistry. Myofibroblasts were identified by alpha smooth muscle actin immunohistochemistry, and matrix metalloproteinase-1 (MMP-1) and MMP-2 were localized with appropriate antisera. Acute interstitial edema was followed by increasing density of glomerular profiles, paralleled by loss of interstitial volume and progressive tubular atrophy. Glomerular profile area remained unchanged. Density of glomerular profiles was not temporally related to myofibroblast accumulation. Procollagen alpha 1(I), alpha 1(III), and alpha 1(IV) transcription was focal, spatially related but temporally ordered. Collagen I, III, and IV immunostaining was increased from days 3, 24, and 100, respectively (P < 0.05 versus day 0 and day 100 saline). However, when corrected for glomerular density, collagen I immunostaining decreased between days 24 and 100, whereas collagen III and IV no longer differed from day 0. MMP staining within the lesion was confined to occasional interstitial and epithelial cells throughout. It is concluded that in this model, contraction and collapse of the tubulointerstitial parenchyma has a greater influence than new collagen production on final fibrotic density.
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PMID:Evolution of tubulointerstitial fibrosis in experimental renal infection and scarring. 955 66

The cartilage of the walls of the trachea and bronchi acts to keep these airways open despite intrathoracic pressure differences during breathing that would otherwise collapse them and limit air flow. Changes in biomechanical properties and composition of airway cartilage may contribute to altered lung function in obstructive lung diseases. To investigate the relationship between collagen organization and equilibrium tensile modulus within the structure of airway cartilage, we used scanning electron microscopy (SEM), histochemistry and equilibrium tensile testing to analyze tracheal cartilage from 10 humans aged 17-81 yr. We show that the surfaces of tracheal cartilage matrix are collagen-rich and surround a proteoglycan-rich core. Collagen fibrils in the superficial zones are oriented in the plane of the cartilage surface. In deeper layers of the cartilage, collagen fibrils are oriented less regularly. Equilibrium tensile modulus of 100 microm thick strips of cartilage was measured and was found to decrease with depth; from 13.6 +/- 1.5 MPa for the ablumenal superficial zone to 4.6 +/- 1.7 MPa in the middle zone (means +/- S.D., n = 10, p < 0.001). Stress-strain curves were linear for strains up to 10% with minimal residual strain. This is consistent with a model in which collagen fibres in the outer layers of the cartilage resist tensile forces, and hydrated proteoglycans in the central zone resist compression forces as the cartilage crescent bends.
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PMID:Ultrastructure and tensile properties of human tracheal cartilage. 959 42

Collagen fibrils in extracellular matrices of connective tissues (tendon, cornea, etc.) are bridged and linked by the anionic glycosaminoglycans (AGAGs) of the small proteoglycans (decoron, etc.). It was proposed that these bridges and ties maintain the collagen fibril dispositions in relation to each other, helping to define tissue shape, and hence called shape modules. This investigation describes chemical and physicochemical conditions in which these structures are stable and what treatments cause their disruption. The effects on fixed and unfixed sections of tendon, cornea, lung and ear from rat, mouse and rabbit of pH, electrolyte concentration, EDTA, mercaptoethanol, hydrogen peroxide, free radicals, periodate, acetylation, urea, nonionic detergent and organic solvents were assessed by staining with Cupromeronic blue or Alcec blue in CEC techniques to localise AGAG bridges or their disintegration products. Ca2+ was not involved in the structures, oxidation/reduction had no effect and Triton X100, a nonionic detergent did not damage them. They were stable between pH 4.5 and 9.5. Periodate as a glycol-cleaving reagent did not affect them. High concentrations of urea (> 2.0 M) and MgCl2 (0.5 M) disrupted the tissues. The combination of Triton and urea at concentrations too low to cause damage separately was disruptive. Free radicals in periodate solutions were damaging. Organic solvents caused collapse and rearrangements of the AGAG filaments. Acetylation caused considerable disruption of shape modules. Dermochondan but not keratan sulphate AGAGs were removed by treatment with NaOH. After fixing with glutaraldehyde only free radical and NaOH treatments were severely disruptive of shape modules. The results are compatible with a previously proposed structure for the shape modules, stabilised by hydrophobic and hydrogen bonding.
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PMID:The structure of interfibrillar proteoglycan bridges (shape modules') in extracellular matrix of fibrous connective tissues and their stability in various chemical environments. 968 5

Collagen molecules in solution unfold close to the maximum body temperature of the species of animal from which the molecules are extracted. It is therefore vital that collagen is stabilized during fiber formation. In this paper, our concept that the collagen molecule is thermally stabilized by loss of configurational entropy of the molecule in the fiber lattice, is refined by examining the process theoretically. Combining an equation for the entropy of a polymer-in-a-box with our previously published rate theory analysis of collagen denaturation, we have derived a hyperbolic relationship between the denaturation temperature, Tm, and the volume fraction, epsilon, of water in the fiber. DSC data were consistent with the model for water volume fractions greater than 0.2. At a water volume fraction of about 0.2, there was an abrupt change in the slope of the linear relationship between 1/Tm and epsilon. This may have been caused by a collapse of the gap-overlap fiber structure at low hydrations. At more than 6 moles water per tripeptide, the enthalpy of denaturation on a dry tendon basis was independent of hydration at 58.55 +/- 0.59 J g-1. Between about 6 and 1 moles water per tripeptide, dehydration caused a substantial loss of enthalpy of denaturation, caused by a loss of water bridges from the hydration network surrounding the triple helix. At very low hydrations (less than 1 mole of water per tripeptide), where there was not enough water to form bridges and only sufficient to hydrogen bond to primary binding sites on the peptide chains, the enthalpy was approximately constant at 11.6 +/- 0.69 J g-1. This was assigned mainly to the breaking of the direct hydrogen bonds between the alpha chains.
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PMID:Polymer-in-a-box mechanism for the thermal stabilization of collagen molecules in fibers. 1035 49

Over its life, an organism's survival and success are determined by the inventory of vital adaptations that its progenitors have creatively appropriated, devised and harnessed along the evolutionary pathway. Such conserved attributes provide the armamentarium necessary for withstanding the adverse effects of natural selection. Refinements of the designs of the respiratory organs have been critical for survival and phylogenetic advancement of animal life. Gas exchangers have changed in direct response to the respiratory needs of whole organisms in different environmental states and conditions. Nowhere else is the dictum that in biology 'there are no rules but only necessities' more manifest than in the evolutionary biology of the gas exchangers. The constructions have been continually fashioned and refined to meet specific needs. Solutions to common respiratory needs have been typified by profound structural convergence. Over the evolutionary continuum, as shifts in environmental situations occurred, infinitely many designs should theoretically have emerged. Moreover, without specific selective pressures and preference for certain designs, considering that there are only two naturally occurring respirable fluid media (air and water), air-lungs, water-lungs, air-gills and water-gills would have formed to similar extents. Factors such as body size, phylogenetic level of development, respiratory medium utilized and habitats occupied have permutatively prescribed the design of the gas exchangers. The construction of the modern gas exchangers has eventuated through painstaking cost-benefit analysis. Trade-offs and compromises have decreed only a limited number of structurally feasible and functionally competent outcomes. The morphological congruity (analogy) of the gas exchangers indicates that similar selective pressures have compelled the designs. Solutions to metabolic demands for molecular O2 have only differed in details. Passive physical diffusion, for example, is the ubiquitous method of transfer of O2 across biological tissues. Gills, evaginated gas exchangers, were the primordial respiratory organs that evolved for water breathing, whereas lungs (invaginated gas exchangers) developed for terrestrial (air) breathing. Transitional (= bimodal = amphibious) breathing has evolved in animals with specialized organs that extract O2 from both water and air. Lungs are tidally (= bidirectionally) ventilated, while gills are unidirectionally ventilated, a feature that allows the highly efficient counter-current disposition between blood and water. Since animals occupy inconstant environmental milieus and their metabolic states vary, gas exchangers are designed to operate optimally across a spectrum of conditions that range from resting to exercise and even under hypoxia. Inbuilt structural and functional flexibility provides the requisite safety factors that allow adjustments to modest pressures. The fundamental structural features that determine the respiratory function of a gas exchanger are respiratory surface area, thickness of the blood-water/gas (tissue) barrier and volume of the pulmonary capillary blood. The diffusing capacity of a gas exchanger correlates directly with the surface area and inversely with the thickness of the blood-water/gas (tissue) barrier. An extensive surface area is generated in gills by extensive stratification of the gas exchanger and in lungs by profuse internal subdivision. Compartmentalization yields small terminal gas exchange compartments that compel greater commitment of energy to ventilate. The surfactant, a phospholipid lining, reduces the forces of surface tension at the air-water interface. This attenuates the propensity of physical collapse of the minute gas exchange units and minimizes the cost of ventilation. The surfactant characterizes all the gas exchangers derived from the piscine air bladder. In the lower air-breathing vertebrates, such as the lungfishes (Dipnoi), amphibians and certain reptiles, the pneumocytes are not differentiated into type I and II cells, as is the case in the lungs of the higher vertebrates-birds and mammals. It is envisaged that in endotherms, the overall numerical density of the pneumocytes and hence the O2 consumption of the gas exchangers may be reduced and a thin blood-gas (tissue) barrier generated, factors that enhance respiratory efficiency. The thin blood-gas (tissue) barriers, for example, those of the mammalian (in the respiratory sections of the interalveolar septum) and avian lungs, consist of an epithelial cell and an endothelial cell with a common basement membrane. An interstitial space occurs in the blood-air/water (tissue) barriers of the gas exchangers of fish gills and lungs of lungfishes, amphibians, reptiles and in the supportive parts of the interalveolar septum of the mammalian lung. Collagen, elastic tissue, nerves, lymphatic vessels and smooth muscle elements are found in the interstitial space. The thickness of the blood-air/water (tissue) barrier allometrically changes very little. This suggests that the thicknesses of the blood-water/air (tissue) barriers have been optimized. The presentation and exposure to the gas exchange media (water/air to blood), features dictated by the geometry and arrangements of the structural components of the gas exchangers, contribute greatly to respiratory efficiency. The countercurrent presentation between water and blood in fish gills is the most efficient design in the evolved gas exchangers: It was imperative for survival in water, a medium that contains relatively less O2 and is more expensive to breathe. In the evolved vertebrate gas exchangers, the exposure of blood to air is best manifested in the diffuse design of the avian lung, where the capillary blood is literally suspended in a three-dimensional air space, the blood being exposed to air virtually across the entire blood-gas (tissue) barrier. A double capillary design occurs in the lungs of amphibians and generally those of reptiles, whereas a single capillary design commonly occurs in those of adult mammals. The capillary loading (the ratio of the volume of the capillary blood to the surface area across which blood is exposed to air) in lungs with a double capillary arrangement is high and manifests a poor design. On the other hand, the low capillary loading that characterizes the single capillary system indicates better exposure of blood to air and greater respiratory capacity. Fractal geometry features in the construction of the gas exchangers. The highly versatile design allows the gas exchangers to function optimally under different conditions and circumstances and to maintain congruent morphologies over a wide range of body size, shape and metabolic capacities. At the gas exchange level, sheet-flow design preponderates in the evolved gas exchangers; blood is efficiently exposed to the external respiratory medium. The respiratory capacity of a gas exchanger is comprehensively granted by refinements of structural features and functional processes. Modelling, mathematical integration of structural and functional parameters, provides a holistic view of the essence of the design of a gas exchanger.
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PMID:Fundamental structural aspects and features in the bioengineering of the gas exchangers: comparative perspectives. 1189 41

This study investigates the impact of different sterilization processes on structural integrity and stability of collagen sponges designed for tissue engineering. Collagen sponges with uniform pore size (20 microm) were sterilized either with ethylene oxide (EO) or gamma irradiation (2.5 Mrad). Gamma-sterilized sponges showed a dramatic decrease of resistance against enzyme degradation and severe shrinkage after cell seeding. Collapsed porosity inhibited fibroblasts and barred completely the human umbilical vein endothelial cell ingrowth into the sponges. On the contrary, the porous structure and stability of EO-sterilized sponges remained almost unaltered. Fibroblasts and endothelial cells exhibited favorable proliferation and migration within sponges with normal morphology. Tubular formation by seeded endothelial cells occurred early in the first week. Therefore, we emphasize that the impact of sterilization of biomaterials is substantial and any new procedure has to be evaluated by correlating the impact of the procedure on the porous structure with cell proliferation behavior.
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PMID:Impact of sterilization on the porous design and cell behavior in collagen sponges prepared for tissue engineering. 1206 25


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