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circadian rhythm
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circadian rhythm

biology
Also known as: daily rhythm, diel rhythm, diurnal rhythm, nychthemeral rhythm, solar day rhythm(Show More)
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circadian rhythm, the cyclical 24-hour period of human biological activity. Within the circadian (24-hour) cycle, a person usually sleeps approximately 8 hours and is awake 16. During the wakeful hours, mental and physical functions are most active and tissue cell growth increases. During sleep, voluntary muscle activities nearly disappear and there is a decrease in metabolic rate, respiration, heart rate, body temperature, and blood pressure. The activity of the digestive system increases during the resting...

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