What is it?
The idea of circadian rhythm is that humans divide their daily behavior into phases of activities (wakefulness) and rest (sleep), which has wide differences in relation to their metabolic need. To live according to its circadian cycle, the human body has developed a biological clock, which aligns its patterns of behavior with the light and darkness of the environment.
How does circadian rhythm control occur?
This control occurs at all levels of the body, from the cell and organelles to the coordination of the organ in the homeotase of blood nutrients. However, it is not only the brain that regulates metabolism, but also the metabolic signals and states themselves also regulate the circadian cycle. With the change in the way modernity lives, many people may have their circadian cycles deregulated, due to the high exposure to screen light until late at night, for example, being able to experience the metabolic consequences of this in the future.
How does circadian rhythm control the organs?
The circadian clock typically regulates some of the most prominent physiological functions in each organ. For example, in the kidney, the circadian clock modulates blood flow, glomerular filtration rate, and excretion of ions and water, which is largely controlled by the rhythmic expression of membrane-transport proteins. In the pancreas, insulin and glucagon secretion is under circadian control, while in muscle, breathing and autophagy follow circadian rhythm. Equally important is rhythmic synthesis and excretion of hormones and other active molecules in peripheral tissues, which provide cross-communication between organs while conducting metabolic programs in distant places in the body.
Circadian cycle and glucose metabolism
Glucose metabolism is an example of circadian regulation of peripheral metabolism, in which several points of metabolism are regulated by the circadian cycle. An example of this is that autonomous liver cell clocks strongly influence glucose production and degradation through different mechanisms and the expression levels of glucose transporters and glucagon receptor reach their peak at the beginning of the activity phase, which coincides with maximum food consumption.
References
Reading suggestion:
Cortisol in circadian rhythm and its effect on the cardiovascular system
Article: Reinke H, Asher G. Crosstalk between metabolism and circadian clocks. Nat Rev Mol Cell Biol. 2019;20(4):227-241. Doi:10.1038/s41580-018-0096-9
