Circadian rhythms are endogenously generated rhythms with a
period length of about 24-hours. A biological clock in the
hypothalamic suprachiasmatic nuclei is responsible for the generation of
circadian rhythms. Notable examples of the circadian rhythms
include the sleep-wake cycle and rhythms in hormone production.
Abnormalities of the circadian system include biological clock lesions
that result in arrhythmic behavior and irregular sleep patterns.
Abnormalities of the circadian system also occur when there is
desynchronization of environmental clock time with the phase of the
“internal milieu” resulting in conditions such as "jet lag".
Numerous aspects of human physiology are greatly influenced by the time
of day, as is the pathogenesis of illness. This review summarizes our current knowledge of the
organization of the circadian system and the generation and regulation
of biological clock function. The role the circadian system plays
in human physiology along with the detection and treatment of biological
clock disorders is also discussed.