2016 Volume 53 Issue 2 Pages 69-81
Twenty-four hour rhythmicity (circadian rhythm) is observed in our physiology (blood pressure and endocrine function etc.) and behavior (sleep-wake cycle) under the real world. Circadian rhythm is driven by internal autonomous clock, so called as circadian pacemaker. In mammals including humans, circadian system is organized in hierarchical multi-oscillators which consist of central circadian pacemaker in the suprachiasmatic nucleus (SCN) of hypothalamus and peripheral organs. The SCN entrains to an external light-dark cycle with a period of 24 h and adjusts autonomously our physiology and behavior. In the modern world, some people are forced to live with an irregular work schedule that becomes desynchronization between his or her circadian clock and sleep-wake cycle. Such abnormal sleep-wake cycle and poor sleep are reported to be a risk factor for metabolic dysfunction and mood disorders. In this review, I will introduce a formal property of circadian clock in humans and effect of our living environment, such as light, meal and exercise, on our internal body clock.
