Based on what you learned in the chapter on control of blood flow and pressure, what must happen to blood flow to meet the metabolic demands of exercising skeletal muscle? How is this accomplished? What is the predicted effect of this change on systemic blood pressure during exercise? What are the changes in heart function during exercise, and what effects should those changes have on systemic
blood pressure? What actually happens to systemic blood pressure during exercise? Explain the apparent contradictions.
What will be an ideal response?
Increased metabolic demands of skeletal muscle require increased blood flow, which is accomplished through
vasodilation. Given the relatively large amount of skeletal muscle in the body, this widespread vasodilation is
expected to produce a decrease in systemic blood pressure. Cardiac output increases through an increase in heart
rate and stroke volume, which is expected to produce an increase in systemic blood pressure. What actually
happens is a slight increase in systemic blood pressure. Part of the predicted decrease from vasodilation is offset by
the fact that many other vessels constrict to redistribute blood flow to the dilated vessels. Total peripheral
resistance, however, does decrease; the expected decrease in systemic blood pressure is offset by the increase in
blood pressure resulting from increased cardiac output. The slight increase seen in systemic blood pressure that
actually occurs during exercise indicates a loss of the normal baroreceptor reflex. The reasons for this are not
understood, but may involve a change in baroreceptor threshold, presynaptic inhibition of baroreceptor afferent
neurons, or influence of an unidentified muscle chemoreceptor.
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