Circadian Rhythms
Circadian rhythms are biological cycles that repeat approximately every 24 hours, regulating numerous physiological and behavioural processes in the body. The term derives from the Latin words “circa” (around) and “dies” (day). These internal rhythms are generated by the body’s own biological clock and are synchronized with external environmental cues, most notably the light-dark cycle. The suprachiasmatic nucleus (SCN), a small region within the brain’s hypothalamus, functions as the master clock that controls and coordinates these rhythms across the body.
Key Functions
Circadian rhythms regulate multiple bodily processes beyond the sleep-wake cycle, including hormone secretion, body temperature, digestion, and immune function. Cortisol levels typically peak in early morning to promote wakefulness, while melatonin production increases in the evening to facilitate sleep. These coordinated changes prepare the body for activity or rest and maintain overall physiological stability.
Regulation and Disruption
Light exposure is the primary regulator of circadian rhythms, with the SCN receiving signals from specialized light-sensitive cells in the retina. This allows the body to align its internal clock with the external environment. Disruptions to circadian rhythms—caused by shift work, jet lag, irregular sleep schedules, or artificial light exposure—can impair sleep quality, cognitive function, and metabolic processes. Maintaining consistent sleep and wake times, as well as managing light exposure, helps preserve healthy circadian function.