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发帖数: 382 | 1 USMLE Step 1 Clinical Question of the Day
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 | P*D
发帖数: 2194 | | l**********e
发帖数: 382 | 3 The correct answer is D. Clearance of a substance will change with
increasing plasma concentration if that substance is secreted or reabsorbed
by a facilitated mechanism. As the concentration of the substance increases,
the transporter becomes saturated, and its contribution to excretion
changes, changing the clearance. If the substance is reabsorbed by a
facilitated mechanism, clearance will eventually increase with increasing
plasma concentrations. Approximately 80% of filtered phosphate is re | l**********e
发帖数: 382 | 4 The correct answer is D. Clearance of a substance will change with
increasing plasma concentration if that substance is secreted or reabsorbed
by a facilitated mechanism. As the concentration of the substance increases,
the transporter becomes saturated, and its contribution to excretion
changes, changing the clearance. If the substance is reabsorbed by a
facilitated mechanism, clearance will eventually increase with increasing
plasma concentrations. Approximately 80% of filtered phosphate is re | l*********0
发帖数: 85 | 5 Thanks for this great question.
I would go for DDDDD. Reabsorption (85%) via sodium/phosphate cotransporter[
2]. Inhibited by parathyroid hormone, especially at high concentration.
C=U*V/P; where U = concentration, V =urine volume / time, U*V = urinary
excretion, and P = plasma concentration.
A creatinine clearance aproach to GFR (higher than real 10-20%)
B mannitol diuretic
C penicillin clearance decrease based on above formula
E urea; reabsorption (50%) via passive transport, transporter would | l*********0
发帖数: 85 | 6 You already did it.
Correct me, if I am wrong. | l**********e
发帖数: 382 | 7 lvboard2010, you are so right, admire |
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