The main distinction between circadian and diurnal rhythm is that circadian rhythm follows a continuous 24-hour cycle of physiological and behavioral rhythms, while diurnal rhythm is periodic and synched only with day and night. Biological rhythms refer to the synchronized cycle exhibited by organisms in response to specific stimuli. These rhythms are regulated by the biological clock, which can be either endogenous, meaning it is controlled by an internal biological clock, or exogenous, meaning it is influenced by external cues. There are several types of biological rhythms, including circadian, diurnal, ultradian, and infradian rhythms.
What is Circadian Rhythm?
Circadian rhythm refers to mental, physical, and behavioral changes that follow a 24-hour cycle. It is influenced by both internal biological factors and external environmental factors such as the natural light and dark cycle. Some factors that can affect circadian rhythms include mutations that affect the biological clock, shift work or changes in time zones that disrupt the light and dark cycle, and exposure to light from electronic devices at night.
Circadian rhythms influence functions such as the release of hormones, eating habits and digestion, and body temperature. Circadian rhythm meets three general criteria. The rhythm has an endogenous free-running period that lasts approximately for about 24 hours. Therefore, the rhythms remain in constant condition. The rhythms are entrainable; therefore, the rhythms are reset due to exposure to external stimuli, which is called entrainment. The rhythms also exhibit temperature compensation. This maintains circadian rhythms over a wide range of physiological temperatures.
What is Diurnal Rhythm?
A diurnal rhythm is a biological rhythm that mainly expresses a periodicity during daylight time as well as night time. Diurnal rhythms may or may not be circadian rhythms and are natural processes that respond mainly to light and dark cycles, affecting animals, plants, and microbes. An example of a diurnal rhythm is the release of microfilariae of Loa loa into the peripheral blood, which occurs predominantly during the daytime. In humans, the maximal microfilaremia levels are generally observed between 10:00 am and 3:00 pm.
Diurnal rhythms are associated with several hormones, including melatonin, cortisol, insulin, glucagon, and estrogen. Therefore, hormonal rhythms are also regulated by diurnal rhythms. The most significant disorder associated with these rhythms is problems due to the body’s internal clock, where the time to sleep or awake is out of sync.
- Circadian rhythm follows a continuous 24-hour cycle of physiological and behavioral rhythms, while diurnal rhythm is periodic and synched only with day and night.
- Circadian rhythm is influenced by both internal biological factors and external environmental factors such as the natural light and dark cycle, while diurnal rhythms respond mainly to light and dark cycles.
- Both circadian and diurnal rhythms are biological rhythms that take place within 24 hours and are regulated by small nuclei in the mid-brain – suprachiasmatic nuclei (SCN).