Physiology of the Pineal Gland and Melatonin

The pineal gland was described as the “Seat of the Soul” by Renee Descartes and it is located in the center of the brain. The main function of the pineal gland is to receive information about the state of the light-dark cycle from the environment and convey this information to produce and secrete the hormone melatonin. The rhythmic production of melatonin, secreted only during the dark period of the day, is extensively used as a marker of the phase of the internal circadian clock. Melatonin itself is used as a therapy for certain sleep disorders related to circadian rhythm abnormalities and for the alleviation of jet lag. It might have more extensive therapeutic applications in the future, since multiple physiological roles have been attributed to melatonin. It exerts physiologic immediate effects during night or darkness and prospective effects at daytime when melatonin levels are undetectable. In addition to its role in regulating the circadian system and sleep patterns, melatonin is involved in cell protection, neuroprotection, and the reproductive system, among other functions. Pineal gland function and melatonin secretion can be impaired due to accidental and developmental conditions, such as pineal tumors, craniopharyngiomas, injuries affecting the sympathetic innervation of the pineal gland, and rare congenital disorders that alter melatonin secretion. This chapter summarizes the physiology and pathophysiology of the pineal gland and melatonin functions. For complete coverage of all related areas of Endocrinology, please visit our on-line FREE web-text, WWW.ENDOTEXT.ORG.