circadian rhythm

/ sər-kā′dē-ən /

1. A daily cycle of biological activity based on a 24-hour period and influenced by regular variations in the environment, such as the alternation of night and day. Circadian rhythms include sleeping and waking in animals, flower closing and opening in angiosperms, and tissue growth and differentiation in fungi.
2. See also biological clock

circadian rhythm

1. An activity cycle lasting twenty-four hours. Many living things, including humans, follow a circadian rhythm. ( See biological clock .)

A Closer Look

The circadian rhythm , present in humans and most other animals, is generated by an internal clock that is synchronized to light-dark cycles and other cues in an organism's environment. This internal clock accounts for waking up at the same time every day even without an alarm clock. It also causes nocturnal animals to function at night when diurnal creatures are at rest. Circadian rhythms can be disrupted by changes in daily schedule. Biologists have observed that birds exposed to artificial light for a long time sometimes build nests in the fall instead of the spring. While the process underlying circadian rhythm is still being investigated, it is known to be controlled mainly by the release of hormones. In humans, the internal clock is located within the brain's hypothalamus and pineal gland, which releases melatonin in response to the information it receives from photoreceptors in the retina. Nighttime causes melatonin secretion to rise, while daylight inhibits it. Even when light cues are absent, melatonin is still released in a cyclical manner.

Example Sentences

Our hormones follow a circadian rhythm, and carbs eaten earlier in the day produce a smaller blood sugar spike compared with carbs eaten later in the day.

From Salon

“We also learned for the first time that part of the mechanism is a disruption of the circadian rhythm of corticosterone, the stress hormone that produces our well-rounded lives.”

From Salon

The theory behind time-restricted eating is that it supports the circadian rhythm, or the body’s internal clock.

From Seattle Times

However, like all living things, plants are subject to a circadian rhythm -- the biological clock that runs through day and night cycles and influences biological processes.

From Science Daily

While most organisms possess circadian rhythms synchronized with the 24-hour day-night cycle, they have also developed other internal clocks to suit their local environments.

From Science Daily