As a result of the lower amplitude of the light/dark cycle, participants with irregular sleep tended to have a delayed secretion of melatonin when compared to the participants with regular sleep.

Melatonin Secretion in Irregular Sleepers

Irregular sleepers had less exposure to light during the day compared to regular sleepers. Irregular sleepers also had a smaller difference between the amount of light they were exposed to during the day and during the night. This suggests that the circadian rhythms of irregular sleepers is delayed.

California Polytechnic State University, San Luis Obispo

Someone with irregular sleep would sleep and wake at random times.

Irregular Sleep

A pattern centered around behavioral, biochemical, or physiological fluctuation that repeats every 24 hours. Major value of a circadian rhythm is synchronizing behaviors and body states with environmental changes, providing temporal organization. 

Circadian Rhythms

Phillips, A. J. K., Clerx, W. M., O’Brien, C. S. et al. Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing. Sci Rep 7, 3216 (2017). https://doi.org/10.1038/s41598-017-03171-4

Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing

Sleep onset and morning awakening time tended to occur later in participants with irregular sleep compared to participants with regular sleep. Participants with irregular sleep also tended to engage in more daytime sleeping than participants with regular sleep.

Irregular Sleep and Sleep Timing

An internal biological clock that allows animals to proceed with their circadian rhythms. Usually, the internal clock is dependent on light. However, animals will still continue their circadian rhythm even in the absence of external cues. For example, even if it is constantly light or dark, animals will proceed with their circadian rhythm. 
- free running

Endogenous clock and circadian rhythm

Circadian Rhythems during the COVID-19 Pandemic

Psychiatry tends to use the circadian cycle to explain illness genesis and illness vulnerability. This is most prominant for mood disorders where a disruption of the 24-hour system occurs before, during and after an episode.

There is also evidence that circadian abnormalities are part of mood disorders functioning as either a cause or a result.

Circadian rhythem involvement in mood disorders

Zeitgebers are environmental cues that help align biological clocks with the external environment. Light is an important cue for setting this clock.

Zeitgebers (time givers)

The sleep-wake cycle is a fundamental circadian rhythm that is internally regulated by the body's biological clock. This process governs the daily pattern of sleeping and waking, ensuring it is synchronized with the 24-hour light-dark cycle of the environment.

Sleep-Wake Cycle

A collection of symptoms that arises from a mismatch between the body's internal circadian cycles and the external environment. A common cause for this desynchronization is traveling across multiple time zones.

Jet Lag

Based on the following case study, analyze the most likely cause of the nurse's symptoms. Explain how the change in their work schedule leads to these specific physiological and psychological effects, referencing the body's internal 24-hour cycle.

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