Question

melatonin is primarily secreted by the ____ gland and plays a significant role in regulating ____ cycles?

Explanation:

Melatonin is a hormone. The pineal gland is known to secrete melatonin. Melatonin is crucial for regulating circadian rhythms (the body's internal 24 - hour clock that controls sleep - wake cycles and other physiological processes).

Answer:

pineal; circadian