What hormone is produced by the pineal gland?

The hormone produced by the pineal gland is melatonin. This gland is located in the brain and plays an essential role in regulating sleep-wake cycles, also known as circadian rhythms. Melatonin levels rise in the evening as it gets dark, signaling to the body that it's time to prepare for sleep, and they decrease in the morning with the light, helping to promote wakefulness.

Melatonin is synthesized from serotonin, which is derived from the amino acid tryptophan. The increased production of melatonin during the night helps to induce sleep, while lower levels during the day help to promote alertness and wakefulness. This hormonal regulation is crucial for maintaining the body's internal clock and ensuring proper sleep patterns.

The other hormones listed, such as insulin and glucagon, are primarily involved in glucose metabolism and are produced by the pancreas, while gibberellin is a plant hormone involved in growth and development. Therefore, melatonin is distinct in its function and origin, highlighting its unique role in human physiology.