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1. Pertaining to the daylight hours; opposite of nocturnal.
2. Repeating once each 24 hours, for example, a diurnal variation or a diurnal rhythm. Compare: circadian.
[L. diurnus, of the day]
Farlex Partner Medical Dictionary © Farlex 2012
circadian rhythmThe diurnal cadence which, in humans (without cyclical cues provided by natural light), is 24.1–24.2 hours (older data had put this figure at 25.4 hours). Photoperiodic information from the eyes synchronises the circadian pacemaker with the light-dark cycle; circadian rhythm affects drug metabolism (e.g., antacids, halothane), serum levels of various substances (in particular adrenocortical hormones) that are routinely measured to detect and monitor disease, physiologic activities (e.g., blood pressure, myocardial blood flow and oxygen demand), psychosomatic disease and sleep cycles, cell division, haematopoiesis and natural killer cell activity.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.
diurnal rhythma pattern of activity based upon a 24-hour cycle, in which there are regular light and dark periods. See also CIRCADIAN RHYTHM.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005