Ahormone involved in the regulation of circadian rhythms, is secreted by the pineal gland.

The answer to this question is Melatonin. Melatonin is a hormone that is made and secreted by the pineal gland that plays a vital role in maintaining the circadian rhythm of our body. Circadian rhythm is our body clock that helps up known when to wake up and sleep. Melatonin helps us regulate sleep and and the body's being awake cycle.

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