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101.
根据下頜光弹的等倾线图,描绘出主应力迹线规迹。在下颌侧位X线照片和去除唇侧及颊侧密质骨板的标本上,观察骨密质和松质的配布,以及骨小梁的排列和方向,试行探讨骨小梁方向与主应力迹线的关系。用光弹法求得的主应力迹线有两个系列:S_1系在下颌体近水平方向,在下颌支近垂直方向分布;S_2系力线与S_1系诸力线呈正交。在标本和X线照片上,主应力迹线规迹不同程度地在骨小梁的排列上有所反映。 相似文献
102.
The primary purpose of the present study was to increase our understanding of the roles of chronicity and controllability in the measurement of stress within the context of stress-illness relationships. Controllability and chronicity were assessed directly using a modified version of the Everyday Problems Scale. In addition to this scale, measures of depression, psychosomatic symptoms, and social support were administered to 128 women and 100 men. The results indicated that, for both men and women, the number of stressors was the best single predictor of symptoms. However, for women, chronicity and controllability of the stressors accounted for a significant amount of the variance in health outcomes over and above that accounted for by the number of stressors endorsed; for men, the addition of neither chronicity nor controllability consistently increased the strength of the association. While available social support was not found to influence the stress-illness relationships, greater willingness to utilize social support was associated with lower levels of depression. 相似文献
103.
104.
The effect of physical training on the cutaneous vascular response during transient exercise load is unclear. We determined the phase response and amplitude response of cutaneous vascular conductance (CVC) in the hand during sinusoidal exercise in endurance exercise-trained and untrained subjects. Subjects exercised on a cycle ergometer with a sinusoidal load for 32 min. The load variation ranged from 10% [23 (1) W in the trained group, 19 (1) W in the untrained group] to 60% [137 (4) W, 114 (6) W] of peak O2 uptake, and five different time periods (1, 2, 4, 8, and 16 min) were selected. Skin blood flow in the dorsal hand and palm were monitored by laser-Doppler flowmetry. CVC was evaluated from the ratio of blood flow to mean arterial pressure. During sinusoidal exercise, the amplitude of CVC was smaller in the dorsal hand than palm for shorter periods (1, 2, and 4 min) (P<0.05). The phase lag of CVC was smaller in the dorsal hand than palm for longer periods (8 and 16 min) (P<0.05). The amplitude response did not differ significantly between the two groups. The phase lag of CVC in the dorsal hand (P<0.05) and palm (P=0.06) was larger in the trained group than untrained group. These findings suggest that glabrous and nonglabrous skin vascular responses in the hand differ during transient exercise load, and physically trained subjects show a slower vascular response in the two skin areas to exercise stimulation than do untrained subjects. 相似文献
105.
Neuromedin B (NMB) is a mammalian bombesin (BN)-like peptide that exerts its function via the neuromedin B receptor (NMB-R). The NMB/NMB-R system is involved in stress response, and therefore we examined behavioral properties in female mice lacking NMB-R using a restraint-induced stress paradigm. Thirty minutes of restraint in a wire mesh cage constituted a sufficient stress stimulus for mice as evidenced by elevated blood glucose concentrations in stressed wild-type and NMB-R-deficient mice. Using a one-trial passive avoidance test, stressed NMB-R-deficient mice exhibited a marked reduction in memory performance. NMB-R-deficient mice exhibited elevated spontaneous activity in a novel environment compared to non-stressed mutant mice after 30-min stress, and a similar difference was also observed between stressed/non-stressed wild-type mice. An elevated plus maze test showed that the stress stimulus had no effect on anxiety in either wild-type or NMB-R-deficient mice. Furthermore, pain response of wild-type and NMB-R-deficient mice induced by electric foot shock was not affected under either stressed or non-stressed conditions. These results indicate that impaired memory performance in stressed NMB-R-deficient mice is not a consequence of changes in spontaneous activity, anxiety, or pain response, and suggest that the NMB/NMB-R pathway may play a role in regulating the stress response via the neural system that controls learning and memory. 相似文献
106.
A.L. Koch 《Research in microbiology》1998,149(10):689
The organization of chains of oligopeptidoglycan in the saccular wall is of critical importance in the study of the mechanism and physiology of prokaryotic wall growth. The electron microphotographs of De Pedro et al, present new findings and can be used to negate or at least raise questions about the previously accepted conclusion that the glycan chains are oriented transversely to the axis of rod-shaped Escherichia coli. This suggests caution in assuming that the glycan chains in the murein structure are parallel to each other and are perpendicular to the axis of the cell.These results should reopen the question of not only the orientation of the peptidoglycan chains, but the possibility of variability in orientation. Three classes of hypotheses about wall growth are reconsidered and problems with them are presented. The new results from De Pedro's laboratory and the experimental glycan chain length distribution argue against proposed systematic models. These include models that postulate belts or hoops stretched around the circumference of the cell and mechanisms that insert new chains of the length of presumptive “docking” strands in the stress-bearing wall. They are consistent, however, with the surface stress theory that proposes that random enzyme action together with physical forces are involved in the elongation of the rod-shaped Gram-negative wall. 相似文献
107.
Variation is an essential feature of biological systems. Populations adapt to dynamic environments, in part, because of this variation. In this review, we re-examine phenotypic variation, especially in organisms living in polluted environments. A recent goal of ecotoxicology is to understand the sublethal effects of exposure to pollutants, e.g. responses to endocrine-disrupting contaminants. While variation is an inherent quality of organisms, variance is a statistical measure of the variation of a trait. Increased variance has been associated with organisms living at the perimeter of a population's range, introduced into novel environments, or exposed to pollution. Some researchers have proposed increased phenotypic variance in exposed populations as an evolutionary mechanism, and others have suggested its use as a biomarker. While we agree that variance often increases in the exposed population, we also recognize that the opposite phenomenon occurs. That is, variance can decrease from exposure to pollution. Altered variance in the exposed population-leading to heteroscedasticity-could result in erroneous conclusions (Type II errors). We suggest that exposure to endocrine-disrupting contaminants could influence the health of populations in ways that are not always represented by measures of central tendency, and that variance and distribution should also be examined in environmentally stressed wildlife. 相似文献
108.
The present study investigates the effects of bis(7)-tacrine, a novel dimeric acetylcholinesterase inhibitor, on hydrogen peroxide(H2O2)-induced cell injury with comparison to the corresponding monomer, tacrine. Exposure of rat pheochromocytoma line PC12 cells to H2O2 induced significant cell damage. This reagent also caused redox desequilibrium as indicated by a decrease in activities of intracellular antioxidant enzymes such as glutathione peroxidase as well as catalase and an accumulation of malondialdehyde, a product of lipid peroxidation. Pretreatment of cells with bis(7)-tacrine or tacrine attenuated H2O2-induced cell toxicity, and bis(7)-tacrine demonstrated higher potency than tacrine in improving redox desequilibrium. These results suggest that bis(7)-tacrine and tacrine significantly protect against H2O2 insult, which might be beneficial for their potential usage in the prevention and treatment of Alzheimer's disease. 相似文献
109.
A dialysis tubing was implanted in the adrenal gland of rats. Adrenomedullary secretion products were dialysed into Ringer solution in the awake animal. Catecholamines (CAs) and methionine-enkephalin (Met-Enk) were measurable under resting conditions. Epinephrine, norepinephrine and Met-Enk-like immunoreactive material increased following application of an immobilization stress for 5 min. The results demonstrate that adrenomedullary CAs and peptides are coreleased. They also demonstrate that Met-Enk-like immunoreactive material is released under stress. 相似文献
110.
C. de Wit Christian Schäfer Philipp von Bismarck Steffen-Sebastian Bolz Ulrich Pohl 《Pflügers Archiv : European journal of physiology》1997,434(4):354-361
We studied whether a flow-independent increase of luminal wall shear stress (WSS) could dilate hamster arterioles in vivo
and which endothelial mediators are potentially involved. To this end the plasma viscosity was elevated by exchanging blood
for dextran-erythrocyte solution thereby augmenting WSS. Diameters of small and large arterioles as well as red blood cell
velocities were measured before and after exchange of blood for solutions of identical haematocrit containing either high-
(HMWD) or low-molecular weight dextran (LMWD). The potential role of endothelial autacoids was investigated by local application
of the NO-synthase inhibitor N
G-nitro-L-arginine (L-NNA), the inhibitor of cyclooxygenase, indomethacin (3 μM), or the K+-channel blocker, tetrabutylammonium (TBA, 0.1 mM) to assess the potential effects of EDHF. HMWD (n = 11 animals) increased plasma viscosity by 64 ± 3% and dilated arterioles of all branching orders (A1–A4) significantly
[by 24 ± 3% (A1–A2) and 32 ± 3% (A3–A4)]. This dilation compensated fully for the calculated initial increase of WSS. LMWD
(n = 6) did not affect plasma viscosity or arteriolar diameters. Tissue treatment with L-NNA (30–300 μM, n = 12) substantially diminished the HMWD-induced dilation in small arterioles (A3–A4; to 13 ± 3%; P<0.05) and virtually abolished it in large ones (A1–A2). Consequently, the calculated WSS increased significantly in these
arterioles (by 31 ± 5%). TBA combined with L-NNA (n = 4) did not reduce further the remaining dilation. Indomethacin (n = 6) had no effect on HMWD-induced dilation. We conclude that an increase of WSS induces a mainly NO-mediated arteriolar
dilation. This dilation occurs in all arteriolar branching orders and is of sufficient magnitude to compensate for the initial
WSS-increase. Thus, any elevations of WSS fulfil the requirement for a signal to change diameter along the arteriolar tree
in a coordinated manner. The fully compensating dilation which we observed indicates that WSS is a controlled variable. It
does, however, raise questions as to its role as a continuous endothelial stimulus.
Received: 2 August 1996 / Received after revision: 24 February 1997 / Accepted: 14 April 1997 相似文献