A physiological mechanism, governed by ‘clock genes’, that regulates the production of proteins that control cycles of sleeping and waking, body temperature, heart activity, hormone secretion, blood pressure, oxygen consumption, metabolism, and other bodily functions according to rhythmic patterns. The master clock, which regulates the 24-hour circadian rhythm, is located in the suprachiasmatic nuclei in the hypothalamus of the brain. Migrating birds and foraging bees navigate partly by reference to the position of the sun; their internal clocks monitor the passage of time and inform them of the anticipated position of the sun at any time of day. See also clock shifting.
Subjects: Zoology and Animal Sciences.