Which one of the following hormones increases the heartbeat in mammals?
- A. Insulin
- B. Melatonin
- C. Thyroxine
- D. Adrenaline ✓
Correct Answer: D. Adrenaline
Explanation
Adrenaline (epinephrine) is released by the adrenal glands during times of stress or excitement, triggering the 'fight or flight' response which increases the heartbeat.
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