graceluv
Forum Newbie
Topics: 8
Posts: 20
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A 35 year old man is referred to the renal clinic for evaluation of proteinuria. He has no other complaint other than foamy urine. Data:
inulin clearance: 100ml/min
plasma osmolarity: 286mOsm/L
plasma [Na+] :140mEq/L
urine flow : 1.44/24hours
urine osmolarity: 205mOsm/L
urine [Na+] :100mEq/L
What amount of Na is reabsorbed?
Ans.
a.14mEq
b.144mEq
c.244mEq
d.20,016mEq
e.20,160mEq
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| paganini
Forum Senior
Topics: 26
Posts: 153
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Answer is D.
First; MAYBE YOU FORGOT TO PUT THE L after 1.44 in urine flow so i ASSUMED THAT 1.44/24H MEANS 1.44 L /24 H
Reabsorption = filtered load- excretion rate
Na+ reabsorption = filtered load - excretion rate
filtered load = GFR x [P]Na(this is plasma concentration of Na+) = GFR x 140 Meq/L
GFR= clearence of inulin = 100ml/min ; But now i need it in L/24 because plasma concentration of Na+ is in L so 100ml/min = 0.1 L/min = 6L/hour (0.1x 60) = 144L/24h(day)
filtered load = 144L/24h x 140 mEq/L= 20,160 mEq/24h
Now we need to get the excretion rate of Na+; Excretion rate= V(urine flow) x [U]Na+ = 1.44L/24h x 100mEq/L = 144mEq/24h
So Reabsorption = 20,160mEq/24h - 144mEq/24h= 20,016mEq/24h
I would like to know if we could get a question like this in step 1 because is a difficult question if you dont use a calculator  , what do you think guys?
I think that the little decrease in plasma osmolarity is maybe because of a decrease in the plasma oncotic pressure (lossing proteins), Remember that filtration across capillaries walls (which separates interstitial fluid from plasma fluid) is under the control of oncotic and hydrostatic pressure) so a decrease in oncoticc pressure drives fluid from interstitial to plasm, diluting it. Na+ reabsorption is normal (99.3% reabsoption). But I am not sure about this, I would like to see other commentaries.
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| graceluv
Forum Newbie
Topics: 8
Posts: 20
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Thanks alot! that was a good one! i really hope such questions don't appear on the real test!
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