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Abstract
<p class="first" id="d2404562e71">Humans and other mammalian species possess an endogenous
circadian clock system that
has evolved in adaptation to periodically reoccurring environmental changes and drives
rhythmic biological functions, as well as behavioural outputs with an approximately
24-hour period. In mammals, body clocks are hierarchically organized, encompassing
a so-called pacemaker clock in the hypothalamic suprachiasmatic nucleus (SCN), non-SCN
brain and peripheral clocks, as well as cell-autonomous oscillators within virtually
every cell type. A functional clock machinery on the molecular level, alignment among
body clocks, as well as synchronization between endogenous circadian and exogenous
environmental cycles has been shown to be crucial for our health and well-being. Yet,
modern life constantly poses widespread challenges to our internal clocks, for example
artificial lighting, shift work and trans-meridian travel, potentially leading to
circadian disruption or misalignment and the emergence of associated diseases. For
instance many of us experience a mismatch between sleep timing on work and free days
(social jetlag) in our everyday lives without being aware of health consequences that
may arise from such chronic circadian misalignment, Hence, this review provides an
overview of the organization and molecular built-up of the mammalian circadian system,
its interactions with the outside world, as well as pathologies arising from circadian
disruption and misalignment.
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