circadian rhythmA biological rhythm or variation that repeats with a cycle of about 24 hours. Circadian rhythms are also known as diurnal rhythms. Examples are waking and sleeping, and variations in temperature, blood pressure, heart rate, glandular secretions, blood sugar levels, and the rate of growth of body cells. See also biological clock. Related category• ANATOMY AND PHYSIOLOGYAlso on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History |