Which hormone released by the sympathetic nerves during exercise increases heart rate?

• A. Acetylcholine
• B. Adrenaline
• C. Noradrenaline
• D. Cortisol

Answer: (B)

Sympathetic activation increases heart rate by sending signals that raise the heart’s pace and strength of contraction. Adrenaline is released into the bloodstream by the adrenal medulla in response to sympathetic activity during exercise. As a circulating hormone, it binds to beta-1 receptors on the heart, speeding up the rate and increasing contractility to deliver more blood to working muscles. Acetylcholine is a parasympathetic transmitter that slows the heart, cortisol acts more on longer-term stress responses and doesn’t cause an immediate heart-rate jump, and noradrenaline is a neurotransmitter released directly from nerves rather than a circulating hormone. So adrenaline best fits the scenario of a hormone released to increase heart rate during exercise.