MCQ Physiology Answer 30

The Correct Answer is D

When muscles contract during exercise, blood flow can increase more than 20-fold. This increase in blood flow is termed active hyperemia. If muscle contraction is occurring during whole body exercise (e.g., running), more than 80% of cardiac output can be directed to the contracting muscles. Therefore, skeletal muscle has a very large flow reserve (or capacity) relative to its blood flow at rest, indicating that the vasculature in resting muscle has a high degree of vascular tone.

This resting tone is brought about by the interplay between vasoconstrictor (e.g., sympathetic adrenergic and myogenic influences) and vasodilator influences (e.g., nitric oxide production, and interstitial adenosine and K+ concentrations).

In the resting state, the vasoconstrictor influences dominate, whereas during muscle contraction, vasodilator influences dominate to increase oxygen delivery to the contracting muscle fibers and to remove metabolic waste products (e.g., lactate, H+, CO2) that accumulate.

Category: Physiology MCQs