circadiens

Circadiens refer to circadian rhythms, endogenous approximately 24-hour cycles that coordinate daily biological processes. They are found in almost all organisms and regulate activities such as sleep, hormone release, metabolism, body temperature, and behavior. While controlled by internal clocks, circadians are entrained by environmental cues, or zeitgebers, with the light-dark cycle being the dominant signal.

At the cellular level, circadian timing in mammals arises from transcription-translation feedback loops. Core clock genes such as CLOCK and BMAL1 activate transcription of PERIOD and CRY genes, whose protein products accumulate and inhibit CLOCK:BMAL1 activity, generating near-24-hour oscillations. Additional loops involving RORs and REV-ERBs modulate BMAL1 expression and help stabilize the system. The master clock resides in the suprachiasmatic nucleus of the hypothalamus, which synchronizes peripheral clocks in tissues throughout the body via neural and hormonal signals.

Entrainment mechanisms include light exposure detected by retinal cells that project to the SCN; this adjusts clock phase through melatonin and cortisol rhythms, among others. Disruption of circadian timing—through shift work, jet lag, or irregular schedules—has been linked to adverse health outcomes, including metabolic and cardiovascular disease, mood disorders, and impaired cognitive function. Chronotherapy and chronopharmacology study how drug effects vary with circadian phase, aiming to optimize treatment timing.

Circadiens are an active area of research across biology, medicine, and chronobiology, with ongoing work to understand their genetic basis, individual variability, and ways to mitigate circadian disruption.