circadianos

Circadianos, known in English as circadian rhythms, are endogenous roughly 24-hour cycles that regulate a wide range of physiological and behavioral processes. They persist in constant conditions but align with the environment through cues such as light and temperature.

In mammals, the central clock resides in the suprachiasmatic nucleus (SCN) of the hypothalamus. Peripheral clocks exist in many tissues, including liver, heart, and immune cells. The molecular mechanism relies on transcription-translation feedback loops involving clock genes such as CLOCK and BMAL1, which activate PER and CRY genes. The protein products of PER and CRY then inhibit CLOCK-BMAL1 activity, creating approximately daily oscillations. Additional components like REV-ERB and ROR help stabilize and fine-tune the cycles.

Entrainment to the environment is primarily driven by light detected by retinal cells containing melanopsin, which transmit signals to the SCN. This alignment allows internal time to track the external day-night cycle. Other cues, including feeding schedules, physical activity, and temperature, can adjust peripheral clocks.

Functions regulated by circadianos include the sleep-wake cycle, hormone secretion (such as melatonin and cortisol), metabolism, cognitive performance, immune responses, and tissue repair. Disruptions from jet lag, shift work, or nighttime screen exposure can desynchronize clocks, potentially increasing risks for sleep disorders and metabolic, cardiovascular, and mood-related conditions.

Advances in chronobiology support applications like chronotherapy and personalized medicine, taking into account individual chronotypes and clock-gene variation to optimize treatment timing and health outcomes.