The hormone that regulates sleep-wake cycles and is produced by the pineal gland?

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

Answer: (A)

Melatonin regulates the sleep-wake cycle and is produced by the pineal gland. The pineal gland synthesizes melatonin from serotonin, with enzymes like AANAT and HIOMT catalyzing the steps. Melatonin levels rise in darkness, signaling to the brain that it’s time to sleep, and are suppressed by light, helping you wake up. This ties directly to the daily rhythm we rely on to feel sleepy at night and alert during the day, which is why melatonin is the hormone linked to sleep-wake regulation from the pineal gland.

Cortisol follows a different pattern, helping wake you up in the morning but not produced by the pineal gland. Adrenaline is part of the fight-or-flight response and isn’t the sleep-regulating hormone produced by the pineal gland. Serotonin is a neurotransmitter involved in mood and is a precursor to melatonin, but the actual sleep-regulating hormone produced by the pineal gland is melatonin.