CHAPTER 8 ■
EXCHANGE FUNCTION OF THE MICROCIRCULATION
A trauma patient in the hospital emer-
gency department is found to have a
venous oxygen saturation (Sv02) of 50%;
arterial oxygen saturation (Sa02) is 95%.
The Sv02 value suggests that
a. Cardiac output is low relative to the
organ oxygen demand.
b. Organ oxygen consumption is
c. Tissue oxygen delivery is elevated.
d. Tissue oxygen extraction is reduced.
Net capillary fluid filtration is enhanced by
a. Decreased capillary plasma oncotic
b. Decreased venous pressure.
c. Increased precapillary resistance.
d. Increased tissue hydrostatic pressure.
If capillary hydrostatic pressure =15 mm
Hg, capillary oncotic pressure = 28 mm
Hg, tissue interstitial pressure = -5 mm
Hg, and tissue oncotic pressure = 6 mm
Hg (assume that 0=1), these Starling
forces will result in
a. Net filtration.
b. Net reabsorption.
c. No net fluid movement.
A malnourished, protein-deficient child
presents with abdominal swelling, which
is determined to be caused by increased
fluid in the abdominal cavity (ascites).
The ascites in this child is most likely
a. Decreased blood volume,
h. Decreased interstitial oncotic pres-
c. Increased capillary reabsorption of
d. Reduced plasma oncotic pressure.
A patient being treated for hypertension
with an arterial vasodilator develops
peripheral edema. The most likely cause
of this edema is
a. Decreased capillary hydrostatic
b. Decreased capillary filtration
c. Increased postcapillary/precapillary
d. Reduced venous pressure.
ANSWERS TO REVIEW QUESTIONS
The correct answer is “a” because
this is the mechanism by which fluid
and accompanying electrolytes move
through capillary intercellular junc-
tions. Choice “b” is incorrect because
diffusion, although an important
mechanism of exchange, is quan-
titatively less important than bulk
flow. Furthermore, electrolytes are
charged ions and therefore do not dif-
fuse through membrane lipid bilayers.
Choice “c” is incorrect because osmo-
sis concerns the movement of water.
Choice “d” is incorrect because vesicu-
lar transport is primarily for the trans-
port of large macromolecules.
The correct answer is “a” because arte-
riolar vasodilation increases blood flow
to the capillaries and increases capillary
P02, which increases the concentra-
tion gradient for diffusion out of the
blood. Choice “b” is incorrect because
decreased arteriolar P02 decreases capil-
lary P02 and therefore the oxygen gradi-
ent between the blood and tissue. Choice
“c” is incorrect because increased tissue
P02 decreases the concentration gradi-
ent for oxygen diffusion from the blood
into the tissue. Choice “d” is incorrect
because a decrease in the number of
flowing capillaries decreases the surface
area available for oxygen exchange.