The pineal gland secretes melatonin, a hormone that controls the daily cycles and acts as the “biological clock”.

The gland involved in the function of our "biological clock" is the pineal gland. The pineal gland, also known as the "third eye," is a small endocrine gland located in the brain. It is shaped like a pinecone, hence its name.

The pineal gland produces a hormone called melatonin, which plays a crucial role in regulating the sleep-wake cycle, also known as the circadian rhythm. The circadian rhythm is the internal biological process that regulates various physiological and behavioral functions over a 24-hour period, including sleep, wakefulness, hormone production, body temperature, and metabolism.

The pineal gland is sensitive to light and darkness. When exposed to light, the production of melatonin is suppressed, signaling the body to be awake and active. Conversely, when it is dark, the pineal gland begins to secrete melatonin, promoting sleep and relaxation.

The secretion of melatonin by the pineal gland follows a diurnal pattern, with higher levels being produced at night and lower levels during the day. This pattern is regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus, which receives information about light and darkness from the eyes and sends signals to the pineal gland to adjust melatonin production accordingly.

The pineal gland's role in regulating the circadian rhythm is crucial for maintaining a healthy sleep-wake cycle. Disruptions in this cycle can lead to sleep disorders, such as insomnia or excessive daytime sleepiness, as well as other health issues, including mood disorders, impaired cognitive function, and an increased risk of chronic diseases.

In addition to its role in regulating the circadian rhythm, the pineal gland is also believed to be involved in other physiological functions, such as the regulation of reproductive hormones, immune system function, and antioxidant production. However, further research is needed to fully understand the extent of its influence on these processes.

In conclusion, the pineal gland is responsible for regulating our "biological clock" through the secretion of melatonin. Its sensitivity to light and darkness helps maintain the circadian rhythm, ensuring proper sleep-wake cycles and overall physiological balance.