European Journal of Molecular & Clinical Medicine

Abstract

The human pineal gland, a part of the diencephalon, is a small neuroendocrine organ that has a function in the circadian rhythm by the secretion of melatonin neurohormone. It is a circumventricular organ because of its deep location in the subarachnoid cistern surrounding the surface of the third ventricle.
Anatomically, the pineal gland is a rounded or crescent-shaped structure like a pine cone and it is attached by the stalk to the diencephalon and the stalk lines the pineal recess whose inferior lip links the pineal gland to the posterior commissure, and superior lip to the habenular commissure.¹
The pineal gland is also considered to be an active neuroendocrine transducer converting neural input, namely a neurotransmitter released at a synapse, to a hormonal output i.e. methoxyindoles of melatonin and polypeptides. In addition it appears that the pineal may itself be subjected to other hormonal signals suggesting endocrine-endocrine and endocrine neural transduction mechanisms. It was only subsequent to the isolation and characterization of melatonin - a secretion of the pineal gland, by Lerner and his coworkers in 1958 that a lot of the functional significance of this enigmatic gland has begun to be unraveled.^2,3
The cyclic nature of the gland's activity earned it the title of a 'biological clock', a switching mechanism regulating the activity of the sex glands in response to the changing seasons and exposure to light and dark. The pineal gland in all mammals produces melatonin in a rhythmic manner with peak levels occurring at night irrespective of whether the animal is nocturnal or diurnal in its behavior pattern. The major functions of pineal melatonin appear to synchronize the seasonal and circadian rhythms of a variety of physiological events