Pineal gland

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Diagram of pituitary and pineal glands.
Gray's FIG. 719– Hind- and mid-brains; postero-lateral view. (Pineal gland near top.)

The pineal gland (also called the pineal body or epiphysis cerebri or epiphysis) is a small pine cone-shaped endocrine organ in the brain. It is located in a sinus on the midline where the two cerebral hemispheres meet the cerebellum. It secretes the hormone melatonin in a circadian pattern with higher levels in the dark and lower levels in the light phase.

Location

The pineal gland is a small body about the size of a pea in adult human beings, located just rostro-dorsal to the superior colliculus and behind and beneath the stria medullaris, between the laterally positioned thalamic bodies.It is attached to the roof of the third ventricle and is part of the epithalamus. In human beings it lies deep within the brain ,but in most vertebrates it lies just beneath the skull.

The pineal gland is a midline structure, and is often seen in plain skull X-rays, since it is often calcified.

Structure and composition

The pineal gland consists mainly of pinealocytes, but four other cell types have been identified: interstitial cells, perivascular phagocytes, pineal neurons and peptidergic neuron-like cells.

The pineal gland in humans consists of a lobular parenchyma of pinealocytes surrounded by connective tissue spaces. The gland's surface is covered by a pial capsule. The pinealocyte consists of a cell body with 4-6 processes emerging. Insterstitial cells are located between the pinealocytes. Many capillaries are present in the gland and perivascular phagocytes are located close to these blood vessels. The perivascular phagocytes are antigen-presenting cells. In higher vertebrates neurons are located in the pineal gland,but are absent in rodents. In some species, neuronal-like peptidergic cells are present, which might have a paracrine regulatory function. Human pineal glands contain a variable quantity of gritty material, called brain sand. Chemical analysis of this sand shows that it is composed of calcium phosphate, calcium carbonate, magnesium phosphate, and ammonium phosphate. (Bocchi et al. 1993). Recently, calcite deposits have been described as well (Baconnier et al. 2002).

Function

The pineal gland was originally believed to be a vestigial remnant of a larger organ. In 1960 Dr. Lerner discovered that the pineal gland is responsible for the production of melatonin, which is produced in a circadian rhythm. The retina detects the light, and directly signals and entrains the suprachiasmatic nucleus (SCN). Fibers project from the SCN to the paraventricular nuclei (PVN), which relay the circadian signals to the spinal cord and out via the sympathetic system to superior cervical ganglia, and from there into the pineal gland.

The pineal gland is larger in children, but shrinks at puberty. It may play a role in sexual development. The higher melatonin levels in children may inhibit sexual development. Pineal tumors have in some cases been linked to precocious puberty. When puberty arrives, melatonin production is reduced. However, the absence of a pineal gland in humans does not always have the same effect on sexual development. Removal of the pineal gland in rats results in hypertrophy of the anterior pituitary, the ovaries and the adrenals(Wurtman et al. 1959 ). In hamsters the reproductive organs become small in the winter and increase in the spring. When the pineal is removed the organs do not atrophy in the winter (Reiter ).

Pinealocytes in lower vertebrates have a strong resemblance to the photoreceptor cells of the eye. Some evolutionary biologists believe that the vertebrate pineal gland can be traced to a proto-eye structure in early vertebrate organisms (Klein 2004). Modern birds and reptiles have been found to express the phototransducing pigment melanopsin in the pineal gland. Avian pineal glands are believed to act like the SCN in mammals (Natesan et al. 2002).

In lower vertebrates, the pineal gland is located on the surface of the brain, directly under the skull and contains photoreceptor-like structures that may regulate their biological clock ( Moore et al. 1967). In humans and other mammals, this function is served by the retinohypothalamic system that sets the rhythm within the suprachiasmatic nucleus. Cultural and social interactions produce exposures to artificial light that influence the setting of the suprachiasmatic clock. Evidence for a role for opsin-related light-sensing compounds in the skin of mammals is presently controversial.

Research suggests that the pineal gland may serve a magnetoreceptive function in some animals [http://www.djpineal.org/pineal-gland.htm#Integration (Deutschlander et al.,1999) .

Reports in rodents suggest that the pineal gland may influence the actions of drugs of abuse such as cocaine [1] and antidepressants such as fluoxetine (Prozac)[2]; and contribute to regulation of neuronal vulnerability[3].

Metaphysics and the pineal

The pineal gland was the last endocrine gland to have its function discovered. This combination led to its being a "mystery" gland with myth, superstition and even metaphysical theories surrounding its perceived function.

Rene Descartes,in the seventeenth century, called the pineal gland the "seat of the soul" . The pineal gland is occasionally associated with the sixth chakra (also called Ajna or the third eye chakra in yoga). It is believed by some to be a dormant organ that can be awakened to enable "telepathic" communication. Madame Blavatsky called the pineal body the "eye of Shiva" and said that in modern man it is a vestigial "organ of spiritual vision".Believers in Discordianism say "consult your pineal".

References
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  • Baconnier,S.,S.B.Lang,M.Polomska,B.Hilczer,G.Berkovic,G.Meshulam.2002.Calcite microcrystals in the pineal gland of the human brain:first physical and chemical studies.Bioelectromagnetics(7):488-495.[[4]]
  • Bocchi,G.,and G.Valdre. 1993.Physical,chemical,and mineralogical characterization of carbonate-hydroxyapatite concretions of the human pineal gland.Journal Inorganic Biochemistry49(3):209-220.[[5]]
  • Deutschlander et al.,1999.[[6]]
  • Klein,D.C. 2004.The 2004 Aschoff/Pittendrigh lecture:Theory of the origin of the pineal gland - a tale of conflict and resolution. Journal of Biological Rhythms 19(4):264-279.[[7]]
  • Macchi,M.M.,and J.N Bruce. 2004. Human pineal physiology and the functional significance of melatonin. Neuroendocrinology 25(3-4):177-195.
  • Moore,R.Y.,A. Heller ,R.J. Wurtman ,J. Axelrod. 1967. Visual pathway mediating pineal response to environmental light. Science 155(759):220–223. PMID 6015532.
  • Natesan,A.,L.Geetha,and M.Zatz. 2002.Rhythm and soul in the avian pineal. Cell Tissue Research 309(1):35-45.[[8]].
  • Wurtman,R.J.,M.D. Altschule, and U.Holmgren. 1959. Effects of Pinealectomy and of a pineal extract in rats.American Journal of Physiology 197:108-110.

External links

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