Melatonin, secreted by the pineal gland, is the primary hormonal regulator of the body's circadian rhythms, most notably the sleep-wake cycle. Its production is tightly controlled by the suprachiasmatic nucleus (SCN) of the hypothalamus, which acts as the master biological clock. Light exposure to the retina inhibits melatonin production, while darkness stimulates it. As night falls, melatonin levels rise sharply, promoting drowsiness and preparing the body for sleep. Its secretion peaks in the middle of the night and declines towards morning, helping to synchronize various physiological processes—such as body temperature, hormone release, and metabolic activity—with the 24-hour light-dark cycle. While other hormones like cortisol also follow a circadian pattern, melatonin is the key chemical signal of darkness and the principal hormonal timekeeper.

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Zambia

• Joseph Soko – 101 pts

• Visual Pathway Lesions
• Positive and Negative Symptoms
• Hallucinations and Delusions
• Antipsychotic Medications
• Emergency: Environmental Emergencies