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circadian rhythm
(redirected from photoperiodic)

    Also found in: Dictionary/thesaurus, Medical, Wikipedia, Hutchinson 0.04 sec.
circadian rhythm: see rhythm, biological rhythm, 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

Inherent cycle of approximately 24 hours in length that appears to control or initiate various biological processes, including sleep, wakefulness, and digestive and hormonal activity. The natural signal for the circadian pattern is the change from darkness to light. The controlling mechanism for these cyclic processes within the body is thought to be the hypothalamus. Any change in the circadian cycle (such as jet lag and other conditions associated with travel) requires a certain period for readjustment.

circadian rhythm [sər′kād·ē·ən ′rith·əm]
(physiology)
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.


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Photoperiodic time tables, hardwired in the mosquitoes during thousands of years of evolution, appeared to be gradually changing in many of the populations--a result, the two scientists say, of warmer temperatures in each population's habitat.
Inherit the warmer wind: some organisms' genes are changing in step ... by Brownlee, Christen / Science News
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