usmleasr
Forum Guru
Topics: 105
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The clearance of several substances was measured at a constant
glomerular filtration rate and constant urine flow rate, but at
increasing plasma concentrations of the substance. Under these
conditions, clearance will increase at high plasma concentrations
for which of the following substances?
A. Creatinine
B. Mannitol
C. Penicillin
D. Phosphate
E. Urea
some one do explain me the important points in clearance :? :roll:
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| usmleasr
Forum Guru
Topics: 105
Posts: 970
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help me please :cry:
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| usmleasr
Forum Guru
Topics: 105
Posts: 970
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dxtxpx.., meg...asmi...someone help me for these qs :?
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| peekay
Forum Guru
Topics: 102
Posts: 588
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i would choose creatinine
reason= all the creatinine that reaches kidney gets out so as plasma concentration of creatinine increases so does its clearence
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| Sakaki-
Forum Senior
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Posts: 238
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Creatinine clearance should remain the same since it is neither reabsorbed or secreted; that's why it is used as an indicator of GFR.
Edit: For clearance to increase, are we looking for a substance that is secreted in the kidneys, not just reabsorbed?
Clearance = (urine concentration)(urine production rate)/plasma concentration
(Raising the plasma creatinine concentration would increase the urine concentration of creatinine by a proportional amount, so clearance would be the same).
Since raising the plasma concentration decreases the gradient for reabsorption, I'm tempted to pick penicillin, which is secreted...
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| asmi
Forum Hero
Topics: 1043
Posts: 4,609
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creatinine..
* since it is filtered and a small amount is secreted ,it always has a clearance slightly greater than GFR and inulin clearance .
* creatine production= Pcr X GFR
net reabsorption ,filtration rate> excretion rate ...for urea ,glucose
net secretion ,filtration rate is < excretion rate ..PAH, creatinine
no net transport ,filtration rate = excretion rate...for inulin,mannitol .
hope iam correct,if wrong do explain..thx
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| usmleasr
Forum Guru
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Posts: 970
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ans is given as phosphate and no explanation given with it :oops:
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| black_tulip
Forum Senior
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High concentration of P in blood---->secretion of PTH--->increase Ca absorption and p excretion
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| asmi
Forum Hero
Topics: 1043
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:arrow: clearance of a substance will change with increasing plasma conc. if that substance is secreted or reabsorbed by facilitated mech .
:arrow: if a substance is reabsorbed by facilitated mech ,clearance will eventually increase with increasing plasma conc's .
:arrow: approx 80 % of filtered phosphate is reabsorbed in the proximal tubule by a sodium-phophate co-transporter...a facilitated mech .
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