The correct answer is “a” because in
response to a reduction in perfusion
pressure and blood flow, the kidney
undergoes autoregulation through dila-
tion of the afferent arterioles. Choice “b”
is incorrect. When the pressure is first
reduced, blood flow will fall by about
30%, but after 2 minutes, the blood
flow will be near normal owing to the
autoregulation. Choice “c” is incorrect
because afferent arteriolar vasodilation
reduces renal vascular resistance. Choice
“d” is incorrect because autoregulation,
by maintaining blood flow, protects the
kidney against ischemia and hypoxia.
The correct answer is “c” because the
increase in flow (reactive hyperemia)
following release of the occlusion causes
a flow-dependent release of nitric oxide
by the vascular endothelium, which
further contributes to the increase in
blood flow. Choice “a” is incorrect
because active hyperemia is associated
with increased tissue metabolic activity
and not with postischemic hyperemia.
Choice “b” is incorrect because vasodila-
tion occurs during ischemia. Choice “d”
is incorrect because increased interstitial
adenosine dilates coronary arterioles.
The correct answer is “c.” Choice “a”
is incorrect because the brain responds
little to sympathetic activation. Although
the coronary vasculature in the heart
(choice “b”) is capable of responding to
sympathetic activation, concurrent stim-
ulation of heart rate and inotropy lead
to metabolic vasodilation. Choice “d” is
incorrect because sympathetic control of
the skin circulation is primarily related to
thermoregulation; therefore, the barore-
ceptor reflex associated with standing has
little influence on cutaneous blood flow.
The correct answers are “f” and “i.”
The correct answers are “b” and “d.”
The correct answer is “e.”
The correct answer is “c.”
The correct answer is “a.”
The correct answer is “g.”
10. The correct answer is “d” and the other
choices are incorrect because in renal
artery stenosis, increased angiotensin
II, which preferentially constricts the
efferent arteriole, helps to maintain
glomerular capillary pressure and filtra-
tion despite the fall in renal perfusion
pressure. Therefore, decreasing angio-
tensin II with an ACE inhibitor removes
this constriction, which leads to a
decrease in glomerular capillary pressure
and glomerular filtration.
11. The correct answer is “a” because coro-
nary artery disease is associated with
endothelial dysfunction and decreased
nitric oxide production. The vasodila-
tor actions of nitric oxide normally
oppose vasoconstrictor mechanisms,
and therefore, reduced nitric oxide
enhances vasoconstrictor responses and
can increase susceptibility to vasospasm.
Choice “b” is incorrect because dimin-
ished sympathetic tone reduces vasocon-
strictor influences on the vessels. Choice
“c” is incorrect because adenosine is a
vasodilator and therefore opposes vaso-
constriction. Choice “d” is incorrect
because endothelin-1 is a vasoconstric-
tor and may contribute to vasospasm.
12. The correct answer is “a” because
increased intracranial pressure reduces
cerebral blood flow by compressing
vessels and increasing their resistance
(therefore, choice “b” is incorrect) and
decreases the effective perfusion pressure,
which can be approximated as the mean
arterial pressure minus the intracranial
pressure (therefore, choice “c” is incor-
rect). Choice “d” is incorrect because the
increased intracranial pressure increases
the pressure outside of the vessels so that
the transmural pressure decreases.
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