The key difference 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.
1. Overview and Key Difference
2. What is Circadian Rhythm
3. What is Diurnal Rhythm
4. Similarities – Circadian and Diurnal Rhythm
5. Circadian vs Diurnal Rhythm in Tabular Form
6. Summary – Circadian vs Diurnal Rhythm
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.
Circadian rhythms allow organisms to anticipate and prepare for precise and regular environmental changes. Circadian rhythms are usually present during the sleep and feeding patterns of organisms. There are patterns in the core body temperature, cell regeneration, brain wave activity, hormone production, and other various biological activities. The common markers used to measure the timing of circadian rhythms in mammals include the secretion of melatonin by the pineal gland, the plasma level of cortisol, and the minimum core body temperature.
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.
What are the Similarities Between Circadian and Diurnal Rhythm?
- Circadian and diurnal rhythms are biological rhythms.
- Moreover, both take place within 24 hours.
- Both are regulated by small nuclei in the mid-brain – suprachiasmatic nuclei (SCN).
- Melatonin controls both rhythms.
- Both perform hormonal controls.
What is the Difference Between Circadian and Diurnal Rhythm?
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. Thus, this is the key difference between circadian and diurnal rhythm. Circadian rhythm is continuous, while diurnal rhythm is periodic. Moreover, the regulation of the sleep-wake cycle is an example of circadian rhythm, while problems due to the body’s internal clock are examples of diurnal rhythm.
The below infographic presents the differences between circadian and diurnal rhythm in tabular form for side-by-side comparison.
Summary – Circadian vs Diurnal Rhythm
Circadian and diurnal rhythms are biological rhythms. 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. Moreover, circadian rhythm meets three general criteria, unlike diurnal rhythms. These include having an endogenous free-running period that lasts approximately 24 hours, being entrainable to external cues such as light and dark cycles, and exhibiting temperature compensation. A diurnal rhythm is a biological rhythm that mainly expresses a periodicity during daylight time as well as night time. The endogenous nature of nature verifies the diurnal rhythms. So, this summarizes the difference between circadian and diurnal rhythm.
1. “Circadian Rhythms.” National Institute of General Medical Sciences, U.S. Department of Health and Human Services.
2. “Diurnal Rhythm – Definition and Examples.” Biology Online Dictionary.
1. “Biological clock human” By YassineMrabet. Information was taken from “The Body Clock Guide to Better Health”. by Michael Smolensky and Lynne Lamberg; Henry Holt and Company, Publishers (2000). (CC BY-SA 3.0) via Commons Wikimedia
2. “Circadian rhythm” By Srruhh – Own work (CC BY-SA 4.0) via Commons Wikimedia
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