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Biological Clocks and Circadian Rhythms

Author: Becky Li

Editors: Emily Yu and Misha Wichita

Artist: Kevin Lin

As the sun sets and the evening begins, you settle in to do your homework, read, or engage in other activities. However, as the night drags on, you notice your eyes drooping and how difficult it is to stay awake. Rest assured, this is a typical sign of a synchronized circadian rhythm! 

Circadian rhythms act as internal clocks, driving physical, mental, and behavioral changes over a 24-hour cycle. They regulate vital functions like sleep patterns, hormone release, and temperature across all organisms, ranging from plants to mammals to micro-organisms. For example, circadian rhythms guide nocturnal animals to remain sheltered in broad daylight and help flowers open or close depending on the time of day. In humans, organs and tissues have their circadian rhythms, such as the endocrine system, which secretes metabolism hormones at normal meal times.

The system regulating an organism’s inner sense of time and circadian rhythms is called the biological clock. Comprising thousands of genes that turn on and off, this clock coordinates the timing of all other biological processes. In vertebrate animals, such as humans, this master clock resides in the hypothalamus as a large group of nerve cells, forming the suprachiasmatic nucleus (SCN). This clock interprets your surrounding environment to direct bodily functions. 

Among its many roles, the SCN regulates melanin production, a hormone that plays a role in sleep, in response to light exposure. Daytime sunlight causes the clock to send signals that promote alertness, while reduced light in the evening triggers increased melatonin production. For this reason, circadian rhythms closely align with day and night cycles, causing you to sleep during the night and be active during the day. 

Besides sleep, the SCN helps control nearly all bodily systems. According to the National Library of Medicine, circadian rhythms impact metabolism and weight through blood sugar and cholesterol regulation. They also affect mental health and the risk of psychiatric illnesses.

Clearly, circadian rhythms are incredibly essential to our everyday lives, but what happens when the biological clock is disrupted? Firstly, there will be sleep issues due to the disturbed sleep-wake cycle. Without proper signaling from the internal clock, you may have trouble falling asleep, wake up frequently during the night, or wake up too early and have difficulty falling back asleep. As a result, there is less quality, restful sleep, and increased daytime fatigue. Memory issues, health problems, and heightened vulnerability to mental health issues may also arise.

Circadian rhythms can fall out of sync for a short or long period due to various factors. Jet lag, which stems from being out of sync with environmental cues in a new time zone, disrupts circadian rhythms until adjustment occurs. During this period, you may experience a lack of sleep and daytime fatigue. Underlying sleep disorders can also disturb rhythms. For example, certain conditions may delay or advance your circadian rhythm, meaning you will sleep and wake later or earlier. Some conditions may lead to an irregular rhythm, resulting in frequent disruptions and waking up during sleep. 

While it’s challenging to alter your circadian rhythm, you can adjust your sleep drive by following routine sleep-wake cycles, modifying meal times as well as caffeine intake, and sleeping at least 7 hours a night. Overall, living a healthy, active lifestyle accompanied by plentiful rest and wise health choices will help you maintain this essential component of your body!



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“Circadian Rhythms: How It Works, What Affects It, and More.” Medical News Today,

MediLexicon International, 11 Jan. 2021,

Silver, Natalie. “Everything to Know About Your Circadian Rhythm.” Healthline, Healthline

Accessed 26 Jan. 2024.

Suni, Eric, and Abhinav Singh. “What Is Circadian Rhythm?” Sleep Foundation, 16 Nov. 2023,

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