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The Endocrine System / The Pineal Gland
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submitted by Dr. Gary Farr - Contact the author here.
Last Updated December, 12, 2011
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What is it?
 The pineal gland, the most enigmatic of endocrine organs, has long been of interest to anatomists. Several millennia ago it was thought to be a valve that controlled the flow of memories into consciousness. René Descartes, the 17th-century French philosopher-mathematician, concluded that the pineal was the seat of the soul. A corollary notion was that calcification of the pineal caused psychiatric disease, a concept that provided support for those who considered psychotic behavior to be rampant; modern examination techniques have revealed that all pineal glands become more or less calcified.
The pineal organ is small, weighing little more than 0.1 gram. It lies deep within the brain between the two cerebral hemispheres and above the third ventricle of the spinal column. It has a rich supply of adrenergic nerve fibers that greatly influence its secretions. Microscopically, the gland is composed of pinealocytes (rather typical endocrine cells except for extensions that mingle with those of adjacent cells). Supporting cells that are similar to astrocytes of the brain are interspersed.
Pineal Gland Functions
The pineal gland contains a number of peptides, including GnRH, TRH, and vasotocin, along with a number of important neurotransmitters such as somatostatin, norepinephrine, serotonin, and histamine. The major pineal hormone, however, is melatonin, a derivative of the amino acid tryptophan. Melatonin was first discovered because it lightens amphibian skin, an effect opposite to that of melanocyte-stimulating hormone of the anterior pituitary. Secretion of melatonin is enhanced whenever the sympathetic nervous system is stimulated. Of greater interest, however, is the fact that secretion increases soon after an animal is placed in the dark; the opposite effect takes place immediately upon exposure to light. Its major action, well documented in animals, is to block the secretion of GnRH by the hypothalamus and of gonadotropins by the pituitary. While it was long thought that a decrease in melatonin secretion heralded the onset of puberty, this hypothesis cannot be supported by studies in humans. It is possible that the pineal contains an as yet unidentified hormone that serves that function.
Melatonin is the major hormone secreted by the pineal gland. (The pineal gland is a tiny endocrine gland situated at the centre of the brain.) Melatonin was discovered in 1958 by Aaron B. Lerner and other researchers working at Yale University. Melatonin is produced in humans, other mammals, birds, reptiles, and amphibians. It is present in very small amounts in the human body.
Melatonin was previously known to cause the skins of amphibians to blanch, but its functions in mammals remained uncertain until research discoveries in the 1970s and '80s suggested that it regulates both sleeping cycles and the hormonal changes that usher in sexual maturity during adolescence. The pineal gland's production of melatonin varies both with the time of day and with age; production of melatonin is dramatically increased during the nighttime hours and falls off during the day, and melatonin levels are much higher in children under age seven than in adolescents and are lower still in adults. Melatonin apparently acts to keep a child's body from undergoing sexual maturation, since sex hormones such as luteotropin, which play a role in the development of sexual organs, emerge only after melatonin levels have declined. This hypothesis is supported by the fact that children with tumors of the pineal gland often reach sexual maturity unusually early in life, presumably because the pineal's production of melatonin has been hampered. Melatonin also seems to play an important role in regulating sleeping cycles; test subjects injected with the hormone become sleepy, suggesting that the increased production of melatonin coincident with nightfall acts as a fundamental mechanism for making people sleepy. With dawn the pineal gland stops producing melatonin, and wakefulness and alertness ensue. The high level of melatonin production in young children may explain their tendency to sleep longer than adults.
In mammals other than humans melatonin possibly acts as a breeding and mating cue, since it is produced in greater amounts in response to the longer nights of winter and less so during summer. Animals who time their mating or breeding to coincide with favorable seasons (such as spring) may depend on melatonin production as a kind of biological clock that regulates their reproductive cycles on the basis of the length of the solar day.
Pineal tumors are rare, occurring most often in children and young adults. The most common of these are germ cell tumors (germinomas and teratomas), which arise from embryonic remnants of germ cells. These tumors are malignant and invasive and may be life-threatening. Tumors of pinealocytes also occur and vary in their potential for malignant change.
Pineal tumors may cause headache, vomiting, and seizures due to the increase in pressure within the head that results from the enlarging tumor mass. Endocrinologic effects may also be observed. Some patients may become hypogonadal with regression of secondary sex characteristics, while others may undergo precocious puberty because of secretion of chorionic gonadotropin. Diabetes insipidus is frequently associated and is usually due to tumor invasion of the hypothalamus and posterior pituitary. Invasion of the pituitary stalk may interfere with the ongoing inhibition of prolactin secretion by dopamine from the hypothalamus, resulting in elevated serum prolactin levels, a finding that may lead to a mistaken diagnosis of prolactinoma. Treatment consists of surgical relief of the increased intracranial pressure and X-ray therapy.
The following reflexes may be active when the pineal gland is involved:
These reflexes should be tested and treated with the proper supplementation.
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