Which hormone is primarily involved in regulating seasonal physiological changes and sleep-wake cycles?

Melatonin is the hormone primarily involved in regulating seasonal physiological changes and sleep-wake cycles. It is produced by the pineal gland in response to darkness, signaling the body that it is time to sleep. This process is integral to the circadian rhythm, which is the body’s internal clock that dictates sleep patterns and various physiological processes over a 24-hour cycle.

The secretion of melatonin increases in the evening, allowing for the facilitation of sleep onset, and decreases during the day in response to light exposure. This hormone plays a vital role in telling the body when to sleep and when to wake, which can be influenced by seasonal changes, such as the length of daylight in different seasons.

While cortisol is another important hormone that affects metabolism and stress responses throughout the day, it peaks in the early morning and is not directly involved in regulating sleep patterns like melatonin. Serotonin is a precursor to melatonin and plays a role in mood regulation, but it does not directly regulate sleep-wake cycles. Dopamine is associated with reward and motivation rather than sleep regulation. Thus, melatonin is the clear answer when it comes to both seasonal changes and sleep-wake cycle regulation.