What is the Difference Between Circadian and Diurnal Rhythm?

Circadian and diurnal rhythms are types of biological rhythms that influence various physiological and behavioral processes in living organisms. Here are the key differences between the two:

• Circadian Rhythms: These are endogenously generated rhythms with a period close to 24 hours. They include sleep/wakefulness cycles, body temperature, hormone secretion, blood pressure, digestive secretions, levels of alertness, and reaction times. Circadian rhythms are influenced by external factors such as light and darkness, and they help regulate functions like sleep schedules, appetite, body temperature, hormone levels, alertness, daily performance, and blood pressure.
• Diurnal Rhythms: These are circadian rhythms that are synchronized with the day/night cycle. A diurnal rhythm refers to an organism being active during the day and sleeping during the night. It is a biological rhythm that is synchronized with the day/night cycle, and it may or may not be a circadian rhythm.

In summary, circadian rhythms are 24-hour cycles that encompass various physiological and behavioral processes, while diurnal rhythms are circadian rhythms that are specifically synchronized with the day/night cycle.

Comparative Table: Circadian vs Diurnal Rhythm

Here is a table comparing the differences between circadian and diurnal rhythms:

In summary, circadian rhythms follow a continuous 24-hour cycle and are entrainable to external cues, while diurnal rhythms are periodic and synced only with day and night. Diurnal rhythms may or may not be circadian rhythms and are natural processes that respond to daylight and darkness. Almost all diurnal rhythms that occur under natural conditions continue to cycle under laboratory conditions under constant light or constant darkness.