A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., endogenous) and responds to the environment (entrained by the environment). These 24-hour rhythms are driven by a circadian clock, and they have been widely observed in animals, plants, fungi and cyanobacteria. The term circadian comes from the Latin circa, meaning "around" (or "approximately"), and diēm, meaning "day". Processes with 24-hour cycles are more generally called diurnal rhythms; diurnal rhythms should not be called circadian rhythms unless they can be confirmed as endogenous, and not environmental. Although circadian rhythms are endogenous, they are adjusted to the local environment by external cues called zeitgebers (German for "time givers"), which include light, temperature and redox cycles. In clinical settings, an
Un ritmo circadiano (), o ciclo circadiano, es un proceso natural, interno que regula el ciclo sueño-vigilia y se repite aproximadamente cada 24 horas. Puede referirse a cualquier proceso que se origina dentro de un organismo (es decir, endógeno) y responde al medio ambiente (entrenado por el medio ambiente). Estos ritmos de 24 horas son impulsados por un reloj circadiano, y han sido ampliamente observados en animales, plantas, hongos y cianobacterias. El término circadiano proviene del latín circa, que significa "alrededor" (o "aproximadamente"), y diēm, que significa "día". Los procesos con ciclos de 24 horas son más generalmente llamados ritmos diurnos; los ritmos diurnos no deben ser llamados ritmos circadianos a menos que puedan ser confirmados como endógenos, y no ambientales. Aunque los ritmos circadianos son endógenos, se ajustan al ambiente local por los cugebers externos llamados "tempo alemán", que incluyen un ciclo de luz.