In most species--from cyanobacteria to humans--genetically encoded circadian clocks have evolved to adapt behavioral and physiological processes to environmental changes brought about by the Earth's rotation. Clock disruption, e. g. by shift work, can lead to circadian misalignment, promoting the development of metabolic, immune and cognitive dysfunction. In mammals, a central circadian pacemaker residing in the suprachiasmatic nuclei of the hypothalamus resets subordinate, but semi-independent cellular clocks in tissues such as liver, kidney, adrenal, and many brain areas. Peripheral clocks regulate various endocrine, metabolic and immune processes, whereas central oscillators modulate basic as well as higher brain functions. For the clinical practice it is of major importance to be aware of these physiological rhythms in order to correctly interpret laboratory data and other disease symptoms. Chronomedical therapies can reduce side effects and increase efficacy by optimizing the timing of treatment or directly affect disease state by restoring internal circadian synchrony.
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