Which hormone is associated with the body's fight-or-flight response?

• A. Melatonin
• B. Adrenaline
• C. Insulin
• D. Cortisol

Answer: (B)

During the fight-or-flight response, the body rapidly readies itself for action by activating the sympathetic nervous system, which triggers the adrenal medulla to release adrenaline (epinephrine). This hormone quickly increases heart rate and the force of contraction, dilates airways, redirects blood to the muscles, and promotes the breakdown of glycogen to raise blood glucose. These rapid changes prepare the body to either confront a threat or flee. Melatonin is for sleep-wake cycles, not acute stress. Insulin lowers blood glucose by promoting uptake into cells, which isn’t about mobilizing energy for immediate action. Cortisol supports energy over a longer period and acts more slowly than adrenaline. So adrenaline best fits the immediate fight-or-flight response.