What does the pineal gland primarily secrete?

The pineal gland primarily secretes melatonin, a hormone that plays a crucial role in regulating sleep-wake cycles and circadian rhythms. Melatonin is produced in response to darkness and helps signal the body that it is time to sleep, thus facilitating the body’s natural sleep patterns. This hormone is critical for maintaining healthy sleep cycles and is influenced by light exposure, making it essential for adapting to seasonal changes as well.

While insulin, thyroid hormones, and adrenaline are significant hormones produced by other glands—the pancreas, thyroid gland, and adrenal glands, respectively—they are not secreted by the pineal gland. Insulin regulates blood sugar levels, thyroid hormones control metabolism, and adrenaline is involved in the body's fight-or-flight response. Understanding the role of the pineal gland in melatonin production highlights its importance in sleep regulation and overall circadian health.