CHAPTER 5 • VASCULAR FUNCTION
119
power, and it is directly related to
vessel length and blood viscosity.
Vessel radius is the most important
factor for regulating resistance.
*
The parallel arrangement of vascular
beds in the body reduces overall
resistance. Furthermore, because of
this arrangement, a resistance change
in one vascular bed has minimal
influence on pressure and flow in other
vascular beds.
Changes in large artery resistance
have little effect on total resistance
of a vascular bed because these
vessels normally comprise only a small
percentage of the total resistance of
a vascular bed. In contrast, changes in
small artery and arteriolar resistances
greatly affect total resistance.
Arteries and veins are normally in
a partially constricted state (i.e.,
they possess vascular tone), which
is determined by the net effect of
vasoconstrictor and vasodilator
influences acting upon the vessel.
CVP is altered by changes in thoracic
blood volume and venous compliance.
Gravity, respiratory activity, and
the pumping action of rhythmically
contracting skeletal muscle have
important influences on CVP.
Cardiac output is strongly influenced
by changes in systemic vascular
function as described by cardiac and
systemic vascular function curves.
In the normal heart, cardiac output
is limited by factors that determine
vascular function.
REV EW QUEST ONS
For each question, choose the one best
answer:
1.
Concerning different types of blood ves-
sels in a vascular network,
a. Arterioles have the highest individual
resistance and, therefore, as a group
of vessels, have the greatest pressure
drop.
b. Capillaries as a group of vessels con-
stitute the greatest resistance to flow
within an organ.
c. Capillaries and venules are the pri-
mary site for fluid exchange.
d. Large arteries are the most important
vessels for blood flow and pressure
regulation.
2.
A 17-year-old male patient who runs
on the high school cross-country team
is found to have an arterial pressure of
115/60 and a resting heart rate of
55 beats/minute. The most likely
explanation for his elevated arterial pulse
pressure is
a. Decreased mean arterial pressure,
h. Elevated ventricular stroke volume.
c. Increased aortic compliance.
d. Reduced systemic vascular resistance.
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