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  1. Melatonin helps in regulating the 24 hour (diurnal) rhythm of the body.
  2. After the sun sets, the eyes perceive darkness.
  3. This alerts the hypothalamus to release the hormone melatonin which promotes sleep.
  4. On the contrary, when the eyes see sunlight, they send signals to the hypothalamus to stop the release of melatonin.
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Melatonin in a hormone which is secreted by pineal gland . This hormone is otherwise known as biological clock of the body. This hormone plays a major role in regulating the sleep wake cycle.
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