CHAPTER 5 • VASCULAR FUNCTION
121
ANSWERS TO REVIEW QUESTIONS
1.
The correct answer is “c” because these
vessels are the most permeable to fluid.
Choice “a” is incorrect because capil-
laries, not arterioles, have the highest
individual resistance because of their
small diameter. Choice “b” is incorrect
because the large number of parallel
capillaries reduces their overall resis-
tance as a group of vessels. Choice “d” is
incorrect because the small arteries and
arterioles are the primary sites for pres-
sure and flow regulation.
2.
A pathological decrease in aortic com-
pliance, which would increase pulse
pressure, is very unlikely in this young,
healthy adult. Therefore, the correct
answer most likely involves increased
stroke volume, and for this reason choice
“b” is correct. Stroke volume would be
elevated because of the low resting heart
rate and perhaps more forceful ventricu-
lar contractions because of exercise con-
ditioning. Choice “a” is incorrect because
aortic compliance increases at lower aor-
tic pressures and volumes; therefore, this
would decrease pulse pressure. Choice
“c” is incorrect because increased aortic
compliance decreases pulse pressure.
Choice “d” is incorrect because reduced
systemic vascular resistance has no effect
on pulse pressure except if mean arterial
pressure is reduced, which would then
decrease pulse pressure.
3.
The correct answer is “c.” Choices “a”
and “b” are incorrect because reduc-
ing heart rate by 10% without changing
stroke volume decreases cardiac output
by 10%. Because mean arterial pres-
sure is also reduced by 10% and mean
arterial pressure equals cardiac output
times systemic vascular resistance (when
central venous pressure is zero), sys-
temic vascular resistance is not changed.
Choice “d” is incorrect because systemic
vascular resistance changes if the sys-
temic vasculature dilates.
4.
The correct answer is “d” because a
50% increase in diameter will increase
flow by about fivefold because flow is
proportional to radius (or diameter) to
the fourth power in a single vessel seg-
ment (assuming that the pressure gradi-
ent does not change appreciably). Choice
“a” is incorrect because decreasing tem-
perature increases blood viscosity, which
decreases flow. Choice “b” is incorrect
because increasing perfusion pressure by
100% increases flow by twofold. Choice
“c” is incorrect because flow is inversely
related to blood viscosity.
5.
The correct answer is “a” because sys-
temic vascular resistance equals arte-
rial minus venous pressure (mm Hg)
divided by cardiac output (mL/min).
6.
The correct answer is “b” because the
renal artery is the distributing artery to
the kidney, and therefore is in series
with the kidney. Although decreasing the
renal artery diameter by 50% increases its
resistance 16-fold, the total renal resis-
tance increases only about 15% because
the renal artery resistance is about
1% of total renal resistance. Therefore,
flow will decrease (assuming no change
in perfusion pressure) about 13%
because F = AP/R and R is increased by a
factor of 1.15. With increased perfusion
pressure because of the hypertension, the
reduction in flow would be <13%.
7.
The correct answer is “a” because a fall
in cardiac output causes arterial pres-
sure to fall and blood to back up into the
venous circulation, which increases cen-
tral venous pressure. Choices “b” and “c”
are incorrect because increased systemic
venous compliance and decreased blood
volume reduce central venous pressure,
cardiac output, and arterial pressure.
Choice “d” is incorrect because general-
ized sympathetic activation would raise
arterial pressure by increasing systemic
vascular resistance and cardiac output.
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