The biological behaviours follow cyclic pattern in relation to time. The biological cycles may occur annually (circannual) or daily (circadian).
Melatonin secreted by the pineal gland this gland helps in the establishment of circadian rhythms (day/light cycles) in the body. The factors contributing to circadian periods include both the endogenous rhythmicity and environmental events.
Circadian rhythms establish a synchronization between the body’s metabolic processes and behaviour. For example, the circadian rhythm helps to release the hormones on time basis, stimulate the appetite and sleep centers at regular intervals.
Disturbance in circadian rhythms cause alteration in metabolic activities and hormonal cycles.