Which gland is responsible for the release of melatonin?

The pineal gland is responsible for the release of melatonin, a hormone that regulates sleep-wake cycles and circadian rhythms. Located deep within the brain, the pineal gland synthesizes and secretes melatonin in response to darkness, helping signal the body that it is time to sleep. This hormone plays a crucial role in managing various biological processes, including regulating sleep patterns and responding to seasonal changes in day length.

The other glands listed do not produce melatonin. The thyroid gland primarily produces hormones that regulate metabolism, while the adrenal gland produces hormones like cortisol and adrenaline, which are important for stress response. The pituitary gland, often termed the "master gland," regulates other endocrine glands but does not secrete melatonin itself. Thus, the correct identification of the pineal gland highlights its specific function in sleep regulation through melatonin production.