During exercise, epinephrine primarily causes which of the following?

• A. Decreases heart rate and respiration.
• B. Reduces carbohydrate metabolism.
• C. Causes vasodilation in the gut.
• D. Increases heart rate, breathing rate, and carbohydrate metabolism.

Answer: (D)

When exercise begins, the body relies on the sympathetic system to boost performance, and epinephrine drives that response. It acts on receptors in the heart to increase rate and force of contraction, raising heart rate and cardiac output. It also opens airways and supports faster breathing, in part through beta-2 effects in the lungs that promote bronchodilation. At the same time, it stimulates liver and muscle cells to break down glycogen into glucose, raising blood glucose and making carbohydrate energy readily available for the muscles. In short, epinephrine readies the body for rapid, energy-demanding activity by increasing heart rate, breathing, and carbohydrate metabolism.

The other options don’t fit this pattern: epinephrine does not lower heart rate or respiration; it increases them. It does not reduce carbohydrate metabolism; it increases it. And gut vessels are typically constricted, not dilated, during sympathetic activation, so vasodilation in the gut is not the effect of epinephrine in exercise.