What term is used to describe the physiological cycle that repeats approximately every 24 hours?

The term that describes the physiological cycle repeating approximately every 24 hours is "circadian rhythms." These rhythms govern various biological processes, including sleep-wake cycles, hormone release, body temperature, and other vital functions. The name "circadian" derives from the Latin words "circa" (meaning "around") and "diem" (meaning "day"), indicating the cycle's alignment with the cycle of day and night.

Circadian rhythms are influenced by external cues such as light and temperature and are crucial for regulating sleep patterns and overall health. Understanding these rhythms helps explain why humans tend to feel sleepy at night and awake during the day, showcasing the body's natural alignment with the external environment.

In contrast, other terms like diurnal cycles specifically refer to daily patterns but are less commonly used in scientific discussions about biological rhythms. Ultradian rhythms involve cycles shorter than 24 hours, for instance, the cycles of sleep stages that occur multiple times within a night. Infradian rhythms refer to cycles longer than 24 hours, such as the menstrual cycle. Each of these categories serves different biological functions, but circadian rhythms specifically relate to the 24-hour cycle that is fundamental to many organisms.