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NBME 22 Answers

nbme22/Block 3/Question#8

A 38-year-old man who lives at sea level flies to a ...

pH: increased;
HCO3-: increased;
Volume: increased

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 +2  upvote downvote
submitted by mcl(226),

Since you're losing all your bicarb into your pee, you would expect the pH to be more alkaline. Also, since there is decreased Na+/H+ antiport, there is less sodium reabsorbed and therefore increased loss of free fluid to the urine.

mcl  useful figure http://users.atw.hu/blp6/BLP6/HTML/common/M9780323045827-036-f002.jpg +  
joker4eva76  Why wouldn't this be similar to a Type 2 RTA where urinary pH <5.5? +1  
mcl  I can't remember exactly what the question was asking off the top of my head, I think it was asking about relative to normal? But I think you're right in that the alpha intercalated cells (AIC) can still dump H+ into the urine and acidify it to an extent. And, like in RTA2, I don't know that the action of the AIC would be able to overcome the bicarb and acidify the urine enough for it to be the usual pH, so the urine should still be more alkaline compared to baseline. Kinda sucks, pH less than 5.5 should technically be acidic but it's alkaline for pee. +  
mcl  JK, normal urine pH is around 4-8, but I guess they consider closer to 5.5 on the more alkaline side...? I guess I would go more off that the alpha intercalated cells can't completely compensate for the amount of bicarb in the pee due to the CA inhibitor, not so much the actual pH. +  
meningitis  Anhydrase inhibitors also affect the anhydrase inhibitors that are used in the AIC in order to excrete the H+. Here is a link:**http://pedclerk.bsd.uchicago.edu/sites/pedclerk.uchicago.edu/files/uploads/distal_0.png** +3  
mcl  ohhhhhhhhhhhhhhhhhhhhhhh my god duh yes thank you <3 +1  
meningitis  Lol yw!! +  

 +1  upvote downvote
submitted by yotsubato(306),

Its a diuretic, so volume is increased.

HCO3 is increased because acetazolamide reduces reabsorption of HCO3.

pH is increased, because HCO3- is a weak base, so it sucks up stray hydrogen ions in the urine.

 +1  upvote downvote
submitted by meatus(1),

I'm sorry but what am I missing here... I thought the whole point of diuretics is to correct volume overload by diuresis? How would total volume be increased??

niboonsh  the question is asking what would happen to the URINARY ph, bicarb, and volume. dont worry, i misread the question too -_- +5  
link981  Also misread the question, thought about the lab volumes of the BLOOD smh +2  
hyperfukus  yooooo me too!!! this is the second NBME i did this on they purposely don't write urine on the arrow categories to mess u up i swear!!! AHHHHHH +  
medulla  missed this question for the same reason .. still pissed +