Hématose

Résumé

L'hématose ( du grec αἱμάτωσις [ aimátosis ], « action de convertir en sang ») est une transformation chimique du sang, par son enrichissement en dioxygène et son appauvrissement en dioxyde de carbone pendant la respiration. Cet échange gazeux se produit entre le milieu extérieur et le sang d'un animal. Elle est produite par simple diffusion, à la faveur du gradient de pression partielle et sans dépense d'énergie. Principe physiologique De petits organismes, avec un bon rapport surface extérieure/volume, et avec un métabolisme faible, comme les plathelminthes, peuvent survivre sans structures anatomiques spécifiques à l'hématose, en utilisant simplement la surface extérieure de leur corps pour effectuer les échanges gazeux. D'autres organismes plus grands et plus actifs, tels que les amphibiens, utilisent l'échange cutané comme hématose complémentaire aux branchies ou aux poumons. Chez les mammifères, l'hématose se produit entre les capillaires et les alvéoles pulmonair

Source officielle

https://fr.wikipedia.org/wiki/H%C3%A9matose

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Increasing temperature and vapor pressure deficit lead to hydraulic damages in the absence of soil drought

Charlotte Grossiord, Eugénie Isabelle Mas, Laura Mekarni, Leonie Corine Schönbeck, Pascal Turberg

Temperature (T) and vapor pressure deficit (VPD) are important drivers of plant hydraulic conductivity, growth, mortality, and ecosystem productivity, independently of soil water availability. Our goal was to disentangle the effects of T and VPD on plant hydraulic responses. Young trees of Fagus sylvatica L., Quercus pubescens Willd. and Quercus ilex L. were exposed to a cross-combination of a T and VPD manipulation under unlimited soil water availability. Stem hydraulic conductivity and leaf-level hydraulic traits (e.g., gas exchange and osmotic adjustment) were tracked over a full growing season. Significant loss of xylem conductive area (PLA) was found in F. sylvatica and Q. pubescens due to rising VPD and T, but not in Q. ilex. Increasing T aggravated the effects of high VPD in F. sylvatica only. PLA was driven by maximum hydraulic conductivity and minimum leaf conductance, suggesting that high transpiration and water loss after stomatal closure contributed to plant hydraulic stress. This study shows for the first time that rising VPD and T lead to losses of stem conductivity even when soil water is not limiting, highlighting their rising importance in plant mortality mechanisms in the future.

Wiley2022

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Purpose: The aim of this study was to provide a theoretical model to predict the vertical loading rate (VLR) at different slopes and speeds during incline running. Methods: Twenty-nine healthy subjects running at least once a week performed in a randomized order 4-min running trials on an instrumented treadmill at various speeds (8, 10, 12, and 14 km h(-1)) and slopes (- 20%, - 10%, - 5%, 0%, + 5%, + 10%,+ 15%,+ 20%). Heart rate, gas exchanges and ground reaction forces were recorded. The VLR was then calculated as the slope of the vertical force between 20 and 80% of the duration from initial foot contact to the impact peak. Results: There was no difference in VLR between the four different uphill conditions at given running speeds, but it was reduced by 27% at 5% slope and by 54% at 10% slope for the same metabolic demand (similar VO2), when compared to level running. The average VLR measured at maximal aerobic intensity during level running would be decreased by 52.7% at + 5%, by 63.0% at+ 10%, and by 73.3% at+ 15% slope. Moreover, VLR was dependent on the slope in downhill conditions. Conclusion: This study highlights the possibility to use uphill running to minimize rate of mechanical load (i.e., osteoarticular load) from foot impact on the ground and as a time-efficient exercise routine (i.e., same energy expenditure than in level running in less time).

SPRINGER2022

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2018

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