Which gland secretes melatonin?

• A. Pituitary gland
• B. Pineal gland
• C. Thyroid gland
• D. Adrenal gland

Answer: (B)

Melatonin is a hormone that helps regulate our sleep-wake cycle and daily rhythms in response to light and darkness. The gland that secretes it is the pineal gland, a tiny structure deep in the brain. It receives input about whether it’s light or dark from the brain’s clock (the hypothalamic clock) via the nervous system. In darkness, the pineal gland increases melatonin production, which promotes sleepiness and signals that night has begun. Exposure to light suppresses melatonin, helping us wake up.

The other glands listed don’t produce melatonin. The pituitary releases hormones like growth hormone and later hormones that coordinate growth and metabolism; the thyroid releases thyroid hormones that regulate metabolism; the adrenal glands produce stress hormones like cortisol and adrenaline.