Class 11 NEET Biology Chemical Coordination and Integration

(a): Melatonin is a hormone secreted by the pineal gland and retinas of vertebrates. Melatonin secretion by the pineal gland is linked to the dark light cycle of the organism's environment, being greatest at night and lowest by day. The hormone is involved in regulating certain diurnal and seasonal changes in the body, such as the reproductive cycle in seasonally breeding animals. It is used as a drug to treat sleep disorders and symptoms of jet lag.