Dynamic exercise such as running
is associated with a large fall in
systemic vascular resistance as active
muscles dilate. To maintain (and
elevate) arterial pressure, sympathetic
activation and circulating hormones
increase cardiac output and constrict
blood vessels in other major organs of
the body; the abdominothoracic and
skeletal muscle pumps promote venous
return to maintain adequate cardiac
preload conditions.
Cardiovascular responses to exercise
are significantly influenced by the
type of exercise (dynamic versus
static), body posture, physical
conditioning, environmental factors,
age, gender, and the presence of
heart disease.
Pregnancy is associated with an
increase in blood volume and cardiac
output, and a decrease in systemic
vascular resistance and mean arterial
pressure; heart rate gradually increases
during pregnancy.
Arterial hypotension can result from
mechanisms that reduce cardiac output
or cause systemic vasodilation.
Compensatory negative feedback
mechanisms, triggered by hypotension,
help to restore arterial pressure.
Baroreceptor and renal mechanisms
play a prominent role. Failure of these
mechanisms and the expression of
positive feedback mechanism lead to
irreversible shock and death.
Hypertension results from increased
cardiac output, usually caused by
increased blood volume, and from
increased systemic vascular resistance.
Essential hypertension is of unknown
origin, whereas secondary hypertension
results from identifiable causes such as
renal disease, excessive sympathetic
activation, or abnormal levels of
Heart failure occurs when the heart is
unable to supply adequate blood flow
to organs, or when it is able to do so
only at elevated filling pressures. It may
involve systolic dysfunction (depressed
ventricular inotropy) or diastolic
dysfunction (impaired filling).
The body compensates for heart failure
by activating the sympathetic nervous
system, renin-angiotensin-aldosterone
system, and other circulating
hormones. These compensatory
mechanisms increase systemic vascular
resistance, stimulate the heart, and
increase blood volume.
Structural defects in heart valves result
in valve stenosis and/or regurgitation,
which affect pressure and volume
relationships within the heart during
systole and diastole, and lead to
reduced cardiac output and elevated
venous pressures.
For each question, choose the one best
During a moderate level of whole-body
exercise (e.g., running),
a. Arterial pulse pressure decreases
owing to the elevated heart rate.
b. Sympathetic-mediated vasoconstric-
tion occurs in the skin.
c. Systemic vascular resistance increases
owing to sympathetic activation.
d. Vagal influences on the sinoatrial
node are inhibited.
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