Once considered to be an organ of little
functional significance, the pineal gland has now
emerged as a major "neuroendocrine transducer"
gland which converts a neural input into hormonal
output with specific effects on reproductive mechanisms
circadian organization and sleep mechanisms and
Mood. The gland acts as
general synchronizing, stabilizing and moderating
For Several Physiological processes. Available evidence strongly indicates that its hormone melatonin has been designated as the pineal gland is active throughout the life of an equilibrating hormone individual.
The pineal gland of vertebrates develops from the neural crest cells of the roof. In human beings it is deeply situated in the midline of the brain below the corpus cell. It is "ideally placed anatomically to cells integrate and compare information from extra cranial sources and intracranial sites". Calcification which occurs in the human pineal gland is considered to be a physiological process related to its past secretory activity rather than an indicator of present degeneration
REGULATION OF PINEAL GLAND SECRETION
The secretion of melatonin, the major pineal
The suprachiasmatic nucleus, the "master circadian clock", present in the hypothalamus, is largely responsible for this endogenous melatonin rhythm. It controls the activity of the pineal gland through the release of norepinephrine from the sympathetic nerve fibers. Increased release of norepinephrine from the sympathetic nerve fibers in nighttime increases the rate of synthesis of melatonin in the pineal gland. Light-dark cycle entrains the melatonin rhythm generated by the suprachiasmatic nucleus
PINEAL GLAND FUNCTIONS
The pineal gland exerts of its effects on bodily systems through the secretion of its major hormone, melatonin. Biochemical and electrophysiologist techniques have revealed that this hormone acts mainly on mid-brain. Hypothalamus and supra schismatic nucleus, although other areas like hippocampus and substantia nigra have also been implicated. Melatonin increases the concentration of serotonin and catecholamines in these areas of the brain. Since melatonin increases the concentration of biogenic amines, and biogenic amines themselves participate in many of the normal and disturbed functions of the central nervous system like mood and sleep disorders, it is likely that melatonin exerts some of its actions on bodily systems by influencing biogenic amine transmission in the central nervous system.
Melatonin, when administered in physiological doses, mimics the light dark cycle in the induction of photoperiod dependent responses. The hormone acts as a conveyor of photoperiodic information, which is interpreted differently at different times of the year. Hence, in recent years, studies on pineal gland function have focussed mainly in seasonal cycles rather than on daily cycles. The structures and functions of neuroendocrine pineal gland remains an enigma to both philosophers and scientists alike since time immemorial. Some structural and functional mysteries of pineal gland are unfolded to some extent in this article by reviewing the work of various researchers. Recently, a neuronal circuit consisting of seven neurons between retina and pineal gland have been established to relate the effect of light and other rays on its secretion. The various physical properties such as luminescence, electromagnetic field, solar flare, infrared energy are also explained and correlated with the structural and secretion components of the gland. The secretion of pineal gland such as melatonin play an important role in sleep-wake patterns, timings and release of reproductive hormones along with temperature control.
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