The gland that secretes melatonin is the what?

• A. Pineal gland
• B. Pituitary gland
• C. Hypothalamus
• D. Thymus

Answer: (A)

Melatonin is the hormone that helps regulate sleep and daily rhythms, and it is produced by the pineal gland. This small gland sits deep in the brain and responds to low light by increasing melatonin synthesis, signaling the body that it’s time to sleep. Signals from the retina and the brain’s circadian clock guide the pineal gland’s activity—melatonin levels rise at night and fall during the day.

The pituitary gland makes many different hormones and is controlled by the hypothalamus, but it does not secrete melatonin. The hypothalamus orchestrates many endocrine and autonomic functions, yet melatonin production is specific to the pineal gland. The thymus is involved in immune system development and also does not secrete melatonin.