Diurnal Rhythm

A diurnal rhythm refers to any biological process or behavioral pattern that cycles over a 24-hour period in synchronization with the Earth’s day-night cycle. While often used interchangeably with circadian rhythm, the term specifically emphasizes the connection to external light cues rather than just the internal biological clock. In humans and other diurnal organisms, these rhythms dictate the timing of essential functions — such as the morning rise in blood pressure, the evening release of melatonin, and fluctuations in core body temperature — ensuring that physiological activity peaks during daylight hours and recovery occurs during the night.