Melatonin, plays an impoant role in sleep-wake cycle, is secreted by:: (A) Pineal gland, (B) Thyroid gland, (C) Ant. pituitary, (D) Pancreas
Answer is A. Melatonin is an endogenous hormone that is normally secreted by the pineal gland and is believed to be involved with the circadian sleep-wake cycle. Melatonin synthesis and secretion are increased during the dark period of the day and maintained at a low level during daylight hours. This diurnal variation in secretion is brought about by norepinephrine secreted by the postganglionic sympathetic nerves that innervate the pineal gland. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 14. Electrical Activity of the Brain, Sleep--Wake States, & Circadian Rhythms. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.