new_n_lost
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During a bitterly cold winter, an elderly couple is found dead in their apartment. All of their windows are closed and their leaky old furnace is on full.
Which of the following is the primary mechanism by which the toxin involved led to the death of this couple?
A. Decreasing intracellular calcium
B. Inhibition of cytochrome oxidase
C. Inhibition of Na+/K+ ATPase
D. Irreversibly binding to hemoglobin
E. Stimulation of cellular apoptosis
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| rock
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this sounds like carbon monoxide poisoning...and the mechanism is B-inhibition of cytochrome oxidase
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| salmonella
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Co inhibits cytochrome oxidase ,also irreversibly binds to hemoglobin.
differentiate
how to
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| keepgoing
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plz correct me if im wrong i think CN blocks cyto not CO,CO binds irreversibily to hemoglobin and shifts ODC to left.
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| rock
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right keepgoing i was also confused between b and d but then i thought that the treatment is hyperbaric oxygen and it displaces CO from hemoglobin so i choose B...but then i cud be wrong too...lets see what NNL says.
http://www.emedicine.com/ped/topic315.htm
and this is one of the links i found which seems reliable...it mentions both the mechanisms but i thought CO binds more strongly to Hb than O2 but it is not irreversible so i choose B. but i'll wait for your inputs so that i can get another thing straightened out.
Edited by rock on 04/12/07 - 10:04 AM
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| rock
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and yes cyanide definitely blocks cytochrome oxidase.
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| mms
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CO bind to HB with a 240x greater affinity than Oxygen but the binding is not irreversibe.
B?
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| usmle4me
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D. CO poisoning
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| usmlefever
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primary mech is binding to heam but its not an irreversible mech b/c it can be replaced by 100% o2.b is also right b/c ETC is an imp mech in body that makes atp & defect in it can cause death.
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| new_n_lost
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Guys Stop Over Thinking itsz Simple
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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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| keepgoing
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agree but precisly i meant affinity of CO to Hemoglobin is so high that it acts like irreversible and in CO poisioning,it will not dissociate so esaily even at normal or high O2,and yes primary mech wud be D only and for option b b/c binding of CO to oxidase is loosely whereas CN also binds strongly and hence also has potential to cause death...
lets wait for nnl
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| jole
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D
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| rock
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hey NNL...
yu visit and then dont post the answer...i bet yu are sitting on your couch with your laptop and a bag of doritos and having fun at our expense. c'mon out with it now
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| new_n_lost
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Rock ................ R u really thinking there is more to CO poisoning than it Binding to Hemoglobin Irreverseibly sometimes u knw a Aeasy one n hit on it ASAP dont overthink.
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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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| new_n_lost
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The correct answer is D.
This couple died of carbon monoxide poisoning. Carbon monoxide has approximately 240 times the affinity for hemoglobin than does oxygen. In a sense, the hemoglobin-CO dissociation curve is shifted very far to the left compared to the hemoglobin-O2 dissociation curve. This means that the binding of hemoglobin to carbon monoxide is virtually irreversible. (The carbon monoxide that cigarette smokers inhale is cleared only when senescent red cells are phagocytized in the spleen and the hemoglobin is degraded.) In addition, the carbon monoxide shifts the hemoglobin-O2 dissociation curve to the left, making the unloading of O2 to the tissues very difficult. When too much hemoglobin is tied up with carbon monoxide, the person dies. The carbon monoxide-hemoglobin complex has a bright red color; a distinctive feature of carbon monoxide poisoning that can be helpful either at autopsy or in living patients is that this color makes the skin and organs also appear bright cherry red.
Generally, intracellular calcium levels increase, rather than decrease (choice A), with cellular injury or death.
Cytochrome oxidase is inhibited by cyanide (choice B).
Ouabain is an example of a poison that inhibits Na+/K+ ATPase (choice C).
Apoptosis (programmed cell death) is stimulated (choice E) by certain genes (e.g., p53, ced 3,4), glucocorticoids, and aging.
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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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| keepgoing
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thanks nnl but explanation for B option not justified as cytochrome oxidase is inhibited by CO as well but the difference is its loosely bound can cause sign n symptoms of CO poisioning but not that severe like CN binding (irreversible) or irreversbily binding to hemoglobin(b/c all hemoglobin being saturated by CO and shifting ODC far left) can cause i.e death.
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| drmohamed811
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for sure.... D is the CORRECT answer
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| rock
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yup...i guess i got nailed in by an easy one...but i think the word irreversible did me in...i guess i hung on to the literal meaning of it.
but hey...now i know the right thing...so its even better.
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