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#1
03-19-2012
 Banned Steps History: Not yet Posts: 176 Threads: 34 Thanked 117 Times in 69 Posts Reputation: 127
Calculating renal reabsorption!

A 35-year-old man with a history of recurrent urinary tract infections comes to the physician because of pain during urination. He is diagnosed and treated for a urinary tract infection. Because of his history, further investigation is warranted. The following data are obtained from the patient:
Inulin clearance

100 mL/min
Plasma osmolarity
286 mOsm/L
Plasma sodium concentration
140 mEq/L
Urine flow
1.44 L / 24 hour
Urine osmolarity
205 mOsm/L
Urine sodium concentration

100 mEq/L

How much sodium does this patient reabsorb each day?
:sorry::sorry:

[A] 14 mEq
[B] 144 mEq
[C] 244 mEq
[D] 20,016 mEq
[E] 20,160 mEq
 The above post was thanked by: Casandra (03-20-2012), venky2600 (09-01-2012)

#2
03-19-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 647 Times in 409 Posts Reputation: 657

if you can tell me wtf a mEq is (something I've never understood) then I can do this question.

1 mEq = how many mOsm?

because once you have that its just

reabsorption = Filtered load - excretion rate = (GFR x [plasma sodium]) - (urine flow rate x [urine sodium])
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#3
03-19-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 106 Threads: 9 Thanked 74 Times in 43 Posts Reputation: 84

how do you get the GFR?

#4
03-19-2012
 USMLE Forums Scout Steps History: Step 1 Only Posts: 51 Threads: 0 Thanked 21 Times in 19 Posts Reputation: 31

Quote:
 Originally Posted by MedPharm how do you get the GFR?
GFR = INULINE clearance

and guys forget about osmolalilty .. we dont need it .. its all about unit conversion witch i haven't practice yet
#5
03-19-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 647 Times in 409 Posts Reputation: 657

Quote:
 Originally Posted by MedPharm how do you get the GFR?
i assume we use 100 or 120 here (since we dont have inulin or creatinine info).
id try both and see which of the answers i get is on the list of options lol
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#6
03-19-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 106 Threads: 9 Thanked 74 Times in 43 Posts Reputation: 84

if all sucks -> use gut-feeling...i'd go with D and move on
 The above post was thanked by: bunny (03-19-2012), d_wiqed (03-19-2012), doctorFH (03-25-2012), Dr. Mexito (03-22-2012)
#7
03-19-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 647 Times in 409 Posts Reputation: 657

Quote:
 Originally Posted by MedPharm if all sucks -> use gut-feeling...i'd go with D and move on
my gut feeling is E lol
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"inflammable means flammable!? What a country."
 The above post was thanked by: MedPharm (03-19-2012)
#8
03-19-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 106 Threads: 9 Thanked 74 Times in 43 Posts Reputation: 84

my gut feeling says: dude, you calculated something (that didn't work out) and ended up with XXXX-144 so...last digit is 6 -> wish you good luck with that

me: ok, gut-feeling. as i have no better idea
 The above post was thanked by: Joanna (03-19-2012)
#9
03-19-2012
 USMLE Forums Scout Steps History: Not yet Posts: 36 Threads: 2 Thanked 50 Times in 19 Posts Reputation: 60
ans. D. 20,016 mEq

ans. D. 20,016 mEq

Reabsorption= Filtration - Excretion = (GFR x P) - (U x V)

GFR=100ml/min; P=140mEq/L

U=100mEq/L

V=1.44L/24h

Filtration=GFR x P

=100ml/min x 140mEq/1000ml

=14mEq/min

=14mEq x 1440/24h

= 20160mEq/24h

Excretion=U x V

=100mEq/L x 1.44L/24h

=144mEq/24h

Reabsorption= (20160-144)mEq/24h = 20016mEq/24h
 The above post was thanked by: Ali Khaliq (03-05-2016), Casandra (03-20-2012), d_wiqed (03-19-2012), doctorFH (03-25-2012), Joanna (03-19-2012), MedPharm (03-19-2012), steps_8186 (03-19-2012), terminator (03-19-2012), venky2600 (09-01-2012)
#10
03-19-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 106 Threads: 9 Thanked 74 Times in 43 Posts Reputation: 84

my gut-feeling in a mathematical genus
 The above post was thanked by: d_wiqed (03-19-2012), Hitman (03-19-2012), hope12 (05-02-2012)
#11
03-19-2012
 USMLE Forums Guru Steps History: Step 1 Only Posts: 441 Threads: 53 Thanked 258 Times in 153 Posts Reputation: 268

great problem
just dont look at osmolality
gfr=inulin clearance=100*140
but look at the units
its in ml,min
so convert it
GFR=(100*140*60*24)/1000 and unit is meq/Day
now excretion is(1.44*100)=144meq/day
absorbed=filtered -excreted=20016meq
 The above post was thanked by: Ali Khaliq (03-05-2016)
#12
03-21-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 647 Times in 409 Posts Reputation: 657
help!

guys, im really confused

as i see it, it is:

reabsorption = (V x Ux) - (GFR x Px)
=(140x144) - (100x286)
=28700 - 28600
=100

im way off, where am i going wrong :/
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#13
03-21-2012
 USMLE Forums Guru Steps History: 1 + CS Posts: 303 Threads: 57 Thanked 106 Times in 67 Posts Reputation: 116

this is a question from kaplan q bank
a typic wtf type questions...i kept scratching my head
while doing this for 5 min i tried and then gave up and got the next few questions also wrong as i ran out of time
#14
03-22-2012
 USMLE Forums Addict Steps History: Not yet Posts: 138 Threads: 1 Thanked 46 Times in 26 Posts Reputation: 56

Quote:
 Originally Posted by Dr.NickRiviera guys, im really confused as i see it, it is: reabsorption = (V x Ux) - (GFR x Px) =(140x144) - (100x286) =28700 - 28600 =100 im way off, where am i going wrong :/

reabsorption = (GFR x Px) - (V x Ux)

GFR= 100 mL/min= 144 l / 24 h
Px = 140 mEq/L

GFR X Px = 144 x 140 = 20160

V = 1.44 l/ 24 h
Ux = 100 mEq/l

V x Ux = 144 mEq

20160 - 144 = 20,016 mEq
#15
03-06-2017
 USMLE Forums Newbie Steps History: Not yet Posts: 9 Threads: 4 Thanked 0 Times in 0 Posts Reputation: 10

GFR= 100ML/min (convert this to L = 0.1L/min)
V= 1.44L/24 hours (convert this to per min = 1.44/1440mins = 0.001)

resorption= filtered - excretion
resorption = (GFR x Px) - (V x Ux)

resorption= (0.1 x 140) - (0.001 x100)
=13.9 or 14.

#16
03-08-2017
 USMLE Forums Scout Steps History: Not yet Posts: 10 Threads: 3 Thanked 0 Times in 0 Posts Reputation: 10

Answer is D. Just subtracting the amount excreted from the filtered load.
Amt absorbed = Filtered load - Amt excreted
= GFR x Plasma concn - Urinne flow rate x Urine concn
(GFR= 100ml/min = 100x1440 /1000 =144 L/day)

Amt absorbed = 144L/dayx140meq/l - 1.44L/dayx100meq/l
= 20016 meq/day

 Tags Physiology-, Renal-, Step-1-Questions

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