new_n_lost
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A normal, healthy, 25-year-old man lives at the beach. His twin brother has been living in a mountain cabin for the past 2 years. Which of the following indices would be expected to be higher in the man living at sea level?
A. Diameter of pulmonary vessels
B. Erythropoietin production
C. Mitochondrial density in a muscle biopsy
D. Renal bicarbonate (HCO3-) excretion
E. Respiratory rate
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| epica
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A-?
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| shalini.ravi
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erythropoietin prod elevated due to hypoxemia ...b
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| doc179
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A ?
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| usmle4me
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?C
AT HIGH ALTITUDE
decrease pO2 at high altitude
Dilated pulm. vessels....higher
Inc. erythro production....higher
inc. rs rate......higher
sys ph increased ...due to dec.o2 and inc co2
So renal compensation inc HCO3 excretion.....higher
So left with C
Anyone?
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| girl^interrupted
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Response of skeletal muscle mitochondria to hypoxia
This review explores the current concepts relating the structural and functional modifications of skeletal muscle mitochondria to the molecular mechanisms activated when organisms are exposed to a hypoxic environment. In contrast to earlier assumptions it is now established that permanent or long-term exposure to severe environmental hypoxia decreases the mitochondrial content of muscle fibres. Oxidative muscle metabolism is shifted towards a higher reliance on carbohydrates as a fuel, and intramyocellular lipid substrate stores are reduced. Moreover, in muscle cells of mountaineers returning from the Himalayas, we find accumulations of lipofuscin, believed to be a mitochondrial degradation product. Low mitochondrial contents are also observed in high-altitude natives such as Sherpas. In these subjects high-altitude performance seems to be improved by better coupling between ATP demand and supply pathways as well as better metabolite homeostasis. The hypoxia-inducible factor 1 (HIF-1) has been identified as a master regulator for the expression of genes involved in the hypoxia response, such as genes coding for glucose transporters, glycolytic enzymes and vascular endothelial growth factor (VEGF). HIF-1 achieves this by binding to hypoxia response elements in the promoter regions of these genes, whereby the increase of HIF-1 in hypoxia is the consequence of a reduced degradation of its dominant subunit HIF-1[alpha]. A further mechanism that seems implicated in the hypoxia response of muscle mitochondria is related to the formation of reactive oxygen species (ROS) in mitochondria during oxidative phosphorylation. How exactly ROS interfere with HIF-1[alpha] as well as MAP kinase and other signalling pathways is debated. The current evidence suggests that mitochondria themselves could be important players in oxygen sensing. Experimental Physiology (2003)
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| girl^interrupted
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so, is it C?
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| new_n_lost
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The correct answer is A.
A number of physiologic changes occur in a person living at high altitude. The diminished barometric pressure at high altitude causes alveolar hypoxia and arterial hypoxia. Pulmonary vasoconstriction occurs in response to alveolar hypoxia; therefore, the diameter of the pulmonary vessels would be greater in the brother living at sea level. All the other choices describe physiologic processes that would be enhanced by living at high altitude.
Increased erythropoietin production (choice B), caused by arterial hypoxia, leads to increases in hematocrit in people living at high altitude.
Mitochondrial density increases (choice C) in people chronically exposed to the hypoxemia caused by living at high altitude.
At high altitudes, the ventilation rate increases, causing a respiratory alkalosis. The kidney then compensates by increasing the excretion of HCO3- (choice D).
Increasing the rate of respiration (choice E) is a very useful adaptation to the hypoxic conditions of high altitude. The primary stimulus is the hypoxic stimulation of peripheral chemoreceptors.
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| new_n_lost
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Epica U nailed it buddy
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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| usmle4me
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You r right NNL I missed that.
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| new_n_lost
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Guys in this Question the Man Living at Sea level was asked
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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| nandrolone
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Hi NNL i am totally convinced abt ur explanation barrin one point
Is respirstory rate elevated in a person chronically exposed to high altitude environment?
Just a doubt. i dont know the answer. Please explain
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| girl^interrupted
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In the above abstract I got this" In contrast to earlier assumptions it is now established(in 2003) that permanent or long-term exposure to severe environmental hypoxia decreases the mitochondrial content of muscle fibres."
so 2 years is not a long time ..and cant b said that its chronic exposure??
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| rock
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isn't 2 years long enough ?
and i dont know why the pulmonary vessels constrict in response to hypoxia. can someone pls explain that. sorry havent yet read physiology so could be a stupid question. just trying to learn something i dont know.
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| verapamil
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yup the pulmonary vascular sys is the only vessels that constrict in response to hypoxia. the reason for this is to decrease flow in the lungs for optimal gas exchange. 
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