phy 21 - aimhigh

[ArchivalUser]

27. A normal, well-hydrated individual has a plasma osmolarity
of 300 mOsmol/L. A drug is then given to increase
urine flow from 2 mL/min to 6 mL/min but to decrease
urine osmolarity from 800 mOsmol/L to 400 mOsmol/L.
Which of the following most likely also occurred?
(A) Excretion of dissolved substances decreased but
osmolar clearance increased
(B) Excretion of dissolved substances and osmolar
clearance both increased
© Excretion of dissolved substances and osmolar
clearance both decreased
(D) Excretion of dissolved substances increased and
osmolar clearance decreased
(E) The drug eliminated the osmolar gradient in the
medullary interstitium

[ArchivalUser]

C?

[ArchivalUser]

B?

[ArchivalUser]

? d

[ArchivalUser]

oh 3 diff answers!!!!!!!!!

[ArchivalUser]

yep aimhigh...

[ArchivalUser]

27. The correct answer is B. The excretion of dissolved
substances (Ed) = (urine flow × urine osmolarity). The
osmolar clearance (Cosm) = (urine flow × urine osmolarity)/
plasma osmolarity. Therefore, Cosm = Ed/plasma
osmolarity. Because plasma osmolarity did not change,
it is clear that both Cosm and Ed increased or decreased
by the same extent. This fact eliminates choices A and
D. Before treatment, Ed = 2 mL/min × 800 mOsmol/L =
1.6 mOsmol/min. After treatment, Ed = 6 mL/min ×
400 mOsmol/L = 2.4 mOsmol/min. This fact eliminates
choice C.
Thus, the astute student can conclude that drug treatment
increased both Cosm and Ed. But let us continue
with the calculations. Before treatment, Cosm = 1.6treatment, Cosm = 2.4 mOsmol/min/300 mOsmol/L =
8.0 mL/min. Note that drug treatment caused both
Cosm and Ed to increase by 50%.
There is no evidence to support the notion that drug
treatment eliminated the osmolar gradient in the
medullary interstitium (choice E).
mOsmol/min/300 mOsmol/L = 5.3 mL/min. After

[ArchivalUser]

nice Q...