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Related to circadian rhythm: melatonin, Circadian rhythm sleep disorder
circadian rhythm:see rhythm, biologicalrhythm, biological,
cyclic pattern of physiological changes or changes in activity in living organisms, most often synchronized with daily, monthly, or annual cyclical changes in the environment.
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circadian rhythm[sər′kād·ē·ən ′rith·əm]
A self-sustained cycle of physiological changes that occurs over an approximately 24-hour cycle, generally synchronized to light-dark cycles in an organism's environment.