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NBME 24 Answers

nbme24/Block 3/Question#2

A 28-year-old man has a blood pressure cuff placed ...

Adenosine

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 +46  upvote downvote
submitted by drdoom(350),

After the cuff is tied, the cells and tissue distal to the cuff will continue consuming ATP (ATP->ADP), but no fresh blood will be delivered to “clear” what will be an accumulating amount of ADP and other metabolites. ADP (=Adenosine) is itself a proxy of consumption and drives vasodilation of arteries! (Evolution is smart!) Increasing ADP/Adenosine in a “local environment” is a signal to the body that a lot of consumption is occurring there; thus, arteries and arterioles naturally dilate to increase blood flow rates and “sweep away” metabolic byproducts.

lispectedwumbologist  You're a good man. Thank you. +  
drdoom  So glad it helped! +1  
seagull  very well put, thank you +1  
eosinophil_council  Great! +  
aisel1787  gold. thank you! +  




 +3  upvote downvote
submitted by madojo(48),

I don't know if this was the right way i thought about it but i remembered C.H.A.L.K the things that cause vasodilation in skeletal muscle

C - Co2, H - H+, A- adenosine, L - lactate K- K+

drdoom  This is great; these are all proxies of catabolism, i.e., "net" ATP consumption! (ATP->ADP) +  
drdoom  Potassium might be the one that doesn't seem to fit but recall that cells have an H+/K+ antiporter: cells can act as a "sink" for high blood H+; they "take up" H+ (from blood, into cell) but "in exchange" they have to put out a K+ (to maintain a normal electro-gradient). So, as blood acid starts to creep up, cells actually "attempt" to bring it back to equilibrium by sucking up H+ (and putting out K+, which, as you surely recall ;), is the predominant cation within cells). +1  




 +1  upvote downvote
submitted by pmnbp(1),

could someone please explain why adenosine is correct?

drdoom  After the cuff is tied, the cells and tissue distal to the cuff will continue consuming ATP (ATP->ADP), but no fresh blood will be delivered to “clear” what will be an accumulating amount of ADP and other metabolites. ADP (=Adenosine) is itself a proxy of consumption and drives vasodilation of arteries! (Evolution is smart!) Increasing ADP/Adenosine in a “local environment” is a signal to the body that a lot of consumption is occurring there; thus, arteries and arterioles naturally dilate to increase blood flow rates and “sweep away” metabolic byproducts. +1