Pineal gland

Pineal gland
Pineal gland
Illu pituitary pineal glands.jpg
Diagram of pituitary and pineal glands in the human brain
Latin glandula pinealis
Gray's subject #276 1277
Artery superior cerebellar artery
Precursor Neural Ectoderm, Roof of Diencephalon
MeSH Pineal+gland

The pineal gland (also called the pineal body, epiphysis cerebri, epiphysis, conarium or the "third eye") is a small endocrine gland in the vertebrate brain. It produces the serotonin derivative melatonin, a hormone that affects the modulation of wake/sleep patterns and seasonal functions.[1][2] Its shape resembles a tiny pine cone (hence its name), and it is located near the centre of the brain, between the two hemispheres, tucked in a groove where the two rounded thalamic bodies join.

Contents

Location

The pineal gland is reddish-gray and about the size of a grain of rice (5–8 mm) in humans, located just rostro-dorsal to the superior colliculus and behind and beneath the stria medullaris, between the laterally positioned thalamic bodies. It is part of the epithalamus.

The pineal gland is a midline structure shaped like a pine cone [3] , and is often seen in plain skull X-rays, as it is often calcified.

Structure and composition

Pineal gland parenchyma with calcifications.
Micrograph of a normal pineal gland – very high magnification.
Micrograph of a normal pineal gland – intermediate magnification.

The pineal body consists in humans of a lobular parenchyma of pinealocytes surrounded by connective tissue spaces. The gland's surface is covered by a pial capsule.

The pineal gland consists mainly of pinealocytes, but four other cell types have been identified. As it is quite cellular (in relation to the cortex and white matter) it may be mistaken for a neoplasm.[4]

Cell type Description
Pinealocytes The pinealocytes consist of a cell body with 4–6 processes emerging. They produce and secrete melatonin. The pinealocytes can be stained by special silver impregnation methods. Their cytoplasm is lightly basophilic. With special stains, pinealocytes exhibit lengthy, branched cytoplasmic processes which extend to the connective septa and its blood vessels.
Interstitial cells Interstitial cells are located between the pinealocytes. They have elongated nuclei and a cytoplasm which is stained darker than that of the pinealocytes.
Perivascular phagocyte Many capillaries are present in the gland, and perivascular phagocytes are located close to these blood vessels. The perivascular phagocytes are antigen presenting cells.
pineal neurons In higher vertebrates neurons are located in the pineal gland. However, these are not present in rodents.
peptidergic neuron-like cells In some species, neuronal-like peptidergic cells are present. These cells might have a paracrine regulatory function.

The pineal gland receives a sympathetic innervation from the superior cervical ganglion. However, a parasympathetic innervation from the sphenopalatine and otic ganglia is also present. Further, some nerve fibers penetrate into the pineal gland via the pineal stalk (central innervation). Finally, neurons in the trigeminal ganglion innervate the gland with nerve fibers containing the neuropeptide, PACAP. Human follicles contain a variable quantity of gritty material, called corpora arenacea (or "acervuli," or "brain sand"). Chemical analysis shows that they are composed of calcium phosphate, calcium carbonate, magnesium phosphate, and ammonium phosphate.[5] In 2002, deposits of the calcite form of calcium carbonate were described.[6] Calcium, phosphorus[7] and fluoride[8] deposits in the pineal gland have been linked with aging.

Miscellaneous anatomy

Pinealocytes in many non-mammalian vertebrates have a strong resemblance to the photoreceptor cells of the eye. Some evolutionary biologists believe that the vertebrate pineal cells share a common evolutionary ancestor with retinal cells.[9]

In some vertebrates, exposure to light can set off a chain reaction of enzymatic events within the pineal gland that regulate circadian rhythms.[10] Some early vertebrate fossil skulls have a pineal foramen (opening). This correlates with the physiology of the modern "living fossils," the lamprey and the tuatara, and some other vertebrates that have a parietal organ or "third eye," which, in some of them, is photosensitive. The third eye represents evolution's earlier approach to photoreception.[11] The structures of the third eye in the tuatara are homologous to the cornea, lens and retina, though the latter resembles that of an octopus rather than a vertebrate retina. The asymmetrical whole consists of the "eye" to the left and the pineal sac to the right. "In animals that have lost the parietal eye, including mammals, the pineal sac is retained and condensed into the form of the pineal gland."[11]

Unlike much of the rest of the mammalian brain, the pineal gland is not isolated from the body by the blood-brain barrier system;[12] it has profuse blood flow, second only to the kidney.[8]

Fossils seldom preserve soft anatomy. The brain of the Russian Melovatka bird, about 90 million years old, is an exception, and it shows a larger-than-expected parietal eye and pineal gland.[13]

In humans and other mammals, the light signals necessary to set circadian rhythms are sent from the eye through the retinohypothalamic system to the suprachiasmatic nuclei (SCN) and the pineal.

Function

The pineal gland was originally believed to be a "vestigial remnant" of a larger organ. In 1917 it was known that extract of cow pineals lightened frog skin. Dermatology professor Aaron B. Lerner and colleagues at Yale University, hoping that a substance from the pineal might be useful in treating skin diseases, isolated and named the hormone melatonin in 1958.[14] The substance did not prove to be helpful as intended, but its discovery helped solve several mysteries such as why removing the rat's pineal accelerated ovary growth, why keeping rats in constant light decreased the weight of their pineals, and why pinealectomy and constant light affect ovary growth to an equal extent; this knowledge gave a boost to the then new field of chronobiology.[15]

Melatonin is N-acetyl-5-methoxy-tryptamine, a derivative of the amino acid tryptophan, which also has other functions in the central nervous system. The production of melatonin by the pineal gland is stimulated by darkness and inhibited by light.[16] Photosensitive cells in the retina detect light and directly signal the SCN, entraining its rhythm to the 24-hour cycle in nature. 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 (SCG), and from there into the pineal gland. The function(s) of melatonin in humans is not clear; it is commonly prescribed for the treatment of circadian rhythm sleep disorders.

The compound pinoline is also produced in the pineal gland; it is one of the beta-carbolines.[citation needed]

The human pineal gland grows in size until about 1–2 years of age, remaining stable thereafter,[17][18] although its weight increases gradually from puberty onwards.[19][20] The abundant melatonin levels in children are believed to inhibit sexual development, and pineal tumors have been linked with precocious puberty. When puberty arrives, melatonin production is reduced. Calcification of the pineal gland is typical in adults.

Apparently the internal secretions of the pineal gland inhibit the development of the reproductive glands, because in cases where it is severely damaged in children, the result is accelerated development of the sexual organs and the skeleton.[21] In animals, the pineal gland appears to play a major role in sexual development, hibernation, metabolism, and seasonal breeding.[22]

Pineal cytostructure seems to have evolutionary similarities to the retinal cells of chordates.[9] 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.[23]

Studies on rodents suggest that the pineal gland may influence the actions of recreational drugs, such as cocaine,[24] and antidepressants, such as fluoxetine (Prozac),[25] and its hormone melatonin can protect against neurodegeneration.[26]

Pathology

All tumors involving the pineal gland are rare; most (50% to 70%) arise from sequestered embryonic germ cells. They most commonly take the form of so-called germinomas,resembling testicular seminoma or ovarian dysegerminoma. Other lines of germ cell differentiation include embryonal carcinomas; choriocariconmas; mixtures of germinom, embryonal carcinoma, and choriocarcinoma; and , uncommonly, typical teratomas (usually benign). Whether to charcterize these germ cell neoplasms as pinealomas is still a subject of debate, but most pinealophiles favor restricting the terms pinealoma to neoplasms arising from the pineocytes.

Pinelomas

These neoplasms are divided into two catergories, pineoblastomas and pineocytomas,[citation needed] based on their level of differentiation, which in turn, correlates with their neoplastic aggressiveness. The clinical course of patients with pineocytomas is prolonged, averaging 7 years.[citation needed] The manifestations are the consequence of their pressure effects and consist of visual disturbances, headache, mental deterioration, and sometimes dementia-like behaviour.[citation needed] The lesions being located where they are, it is understandable that successful excision is at best difficult.

Metaphysics and philosophy

The secretory activity of the pineal gland is only relatively understood. Historically, its location deep in the brain suggested to philosophers that it possessed particular importance. This combination led to its being a "mystery" gland with myth, superstition and occult theories surrounding its perceived functions.

René Descartes, who dedicated much time to the study of the pineal gland,[27] called it the "seat of the soul."[28] He believed that it was the point of connection between the intellect and the body.[29] Descartes attached significance to the gland because he believed it to be the only section of the brain which existed as a single part, rather than one half of a pair. He argued that because a person can never have "more than one thought at a time", external stimuli must be united within the brain before being considered by the soul, and he considered the pineal gland to be situated in "the most suitable possible place for this purpose", located centrally in the brain and surrounded by branches of the carotid arteries.[27]

Baruch de Spinoza criticized Descartes' viewpoint for neither following from self-evident premises nor being "clearly and distinctly perceived" (Descartes having previously asserted that he could not draw conclusions of this sort), and questioned what Descartes meant by talking of "the union of the mind and the body".[30]

The notion of a "pineal-eye" is central to the philosophy of the French writer Georges Bataille, which is analyzed at length by literary scholar Denis Hollier in his study Against Architecture. In this work Hollier discusses how Bataille uses the concept of a "pineal-eye" as a reference to a blind-spot in Western rationality, and an organ of excess and delirium.[31] This conceptual device is explicit in his surrealist texts, The Jesuve and The Pineal Eye.[32]

The notion of an inner third eye (attributed mystical significance) also occurs in ancient, oriental, and new age philosophies.

Additional images

The pineal body is labeled in these images.

References

  1. ^ Macchi M, Bruce J (2004). "Human pineal physiology and functional significance of melatonin". Front Neuroendocrinol 25 (3–4): 177–95. doi:10.1016/j.yfrne.2004.08.001. PMID 15589268. 
  2. ^ Arendt J, Skene DJ (2005). "Melatonin as a chronobiotic". Sleep Med Rev 9 (1): 25–39. doi:10.1016/j.smrv.2004.05.002. PMID 15649736. "Exogenous melatonin has acute sleepiness-inducing and temperature-lowering effects during 'biological daytime', and when suitably timed (it is most effective around dusk and dawn) it will shift the phase of the human circadian clock (sleep, endogenous melatonin, core body temperature, cortisol) to earlier (advance phase shift) or later (delay phase shift) times." 
  3. ^ Bowen, R.. "The Pineal Gland and Melatonin". http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html. Retrieved 14 October 2011. 
  4. ^ Kleinschmidt-DeMasters BK, Prayson RA (November 2006). "An algorithmic approach to the brain biopsy—part I". Arch. Pathol. Lab. Med. 130 (11): 1630–8. doi:10.1043/1543-2165(2006)130[1630:AAATTB]2.0.CO;2. PMID 17076524. 
  5. ^ Bocchi G, Valdre G (1993). "Physical, chemical, and mineralogical characterization of carbonate-hydroxyapatite concretions of the human pineal gland". J Inorg Biochem 49 (3): 209–20. doi:10.1016/0162-0134(93)80006-U. PMID 8381851. 
  6. ^ Baconnier S, Lang S, Polomska M, Hilczer B, Berkovic G, Meshulam G (2002). "Calcite microcrystals in the pineal gland of the human brain: first physical and chemical studies". Bioelectromagnetics 23 (7): 488–95. doi:10.1002/bem.10053. PMID 12224052. 
  7. ^ "IngentaConnect High Accumulation of Calcium and Phosphorus in the Pineal Bodies". Ingentaconnect.com. 2006-06-16. http://www.ingentaconnect.com/content/hum/bter/2007/00000119/00000002/art00004. Retrieved 2009-07-06. 
  8. ^ a b Luke, Jennifer. "Fluoride Deposition in the Aged Human Pineal Gland". Caries Res 2991 (35): 125–28. http://www.icnr.com/jluke/fluoridedeposition.html. Retrieved 2009-05-20. 
  9. ^ a b Klein D (2004). "The 2004 Aschoff/Pittendrigh lecture: Theory of the origin of the pineal gland—a tale of conflict and resolution". J Biol Rhythms 19 (4): 264–79. doi:10.1177/0748730404267340. PMID 15245646. 
  10. ^ Moore RY, Heller A, Wurtman RJ, Axelrod J. Visual pathway mediating pineal response to environmental light. Science 1967;155(759):220–3. PMID 6015532
  11. ^ a b Schwab, I.R.; O'Connor, G.R. (March 2005). "The lonely eye" (Full text). British Journal of Ophthalmology 89 (3): 256. doi:10.1136/bjo.2004.059105. PMC 1772576. PMID 15751188. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1772576. 
  12. ^ Pritchard, Thomas C.; Alloway, Kevin Douglas (1999) (Google books preview). Medical Neuroscience. Hayes Barton Press. pp. 76–77. ISBN 1889325295. http://books.google.com/?id=m7Y80PcFHtsC&printsec=frontcover#PPA76,M1. Retrieved 2009-02-08. 
  13. ^ Kurochkin, Evgeny N.; Gareth J. Dyke, Sergei V. Saveliev, Evgeny M. Pervushov, Evgeny V. Popov (June 2007). "A fossil brain from the Cretaceous of European Russia and avian sensory evolution" (Full text). Biology Letters (The Royal Society) 3 (3): 309–313. doi:10.1098/rsbl.2006.0617. PMC 2390680. PMID 17426009. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2390680. 
  14. ^ Lerner AB, Case JD, Takahashi Y (1960). "Isolation of melatonin and 5-methoxyindole-3-acetic acid from bovine pineal glands". J Biol Chem 235: 1992–7. PMID 14415935. 
  15. ^ Coates, Paul M. (2005). Encyclopedia of Dietary Supplements. Marc R. Blackman, Gordon M. Cragg, Mark Levine, Joel Moss, Jeffrey D. White. CRC Press. p. 457. ISBN 0824755049. http://books.google.com/?id=Sfmc-fRCj10C&pg=PA457&lpg=PA457&dq=Lerner+melatonin+history. Retrieved 2009-03-31. 
  16. ^ Axelrod J (1970). "The pineal gland". Endeavour 29 (108): 144–8. PMID 4195878. 
  17. ^ Lack of pineal growth during childhood. Schmidt F, Penka B, Trauner M, Reinsperger L, Ranner G, Ebner F, Waldhauser F. J Clin Endocrinol Metab. 1995 Apr;80(4):1221–5.
  18. ^ Development of the pineal gland: measurement with MR. Sumida M, Barkovich AJ, Newton TH. AJNR Am J Neuroradiol. 1996 Feb;17(2):233–6.
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  20. ^ Tapp E, Huxley M. The histological appearance of the human pineal gland from puberty to old age. J Pathol 1972;108:137–144
  21. ^ "The Pineal Body". Human Anatomy (Gray's Anatomy). http://www.theodora.com/anatomy/the_pineal_body.html. Retrieved 2011-09-07. 
  22. ^ Strassman
  23. ^ Natesan A, Geetha L, Zatz M (2002). "Rhythm and soul in the avian pineal". Cell Tissue Res 309 (1): 35–45. doi:10.1007/s00441-002-0571-6. PMID 12111535. 
  24. ^ Uz T, Akhisaroglu M, Ahmed R, Manev H (2003). "The pineal gland is critical for circadian Period1 expression in the striatum and for circadian cocaine sensitization in mice". Neuropsychopharmacology 28 (12): 2117–23. doi:10.1038/sj.npp.1300254. PMID 12865893. 
  25. ^ Uz T, Dimitrijevic N, Akhisaroglu M, Imbesi M, Kurtuncu M, Manev H (2004). "The pineal gland and anxiogenic-like action of fluoxetine in mice". Neuroreport 15 (4): 691–4. doi:10.1097/00001756-200403220-00023. PMID 15094477. 
  26. ^ Manev H, Uz T, Kharlamov A, Joo J (1996). "Increased brain damage after stroke or excitotoxic seizures in melatonin-deficient rats". FASEB J 10 (13): 1546–51. PMID 8940301. 
  27. ^ a b Descartes and the Pineal Gland (Stanford Encyclopedia of Philosophy)
  28. ^ Descartes R. Treatise of Man. New York: Prometheus Books; 2003. ISBN 1-59102-090-5
  29. ^ Descartes R. "The Passions of the Soul" excerpted from "Philosophy of the Mind", Chalmers, D. New York: Oxford University Press, Inc.; 2002. ISBN 978-0-19-514581-6
  30. ^ http://en.wikisource.org/wiki/Ethics_%28Spinoza%29/Part_5
  31. ^ Hollier, D, Against Architecture: The Writings of Georges Bataille, trans. Betsy Wing, MIT, 1989.
  32. ^ Bataille, G, Visions of Excess: Selected Writings, 1927–1939 (Theory and History of Literature, Vol 14), trans. Allan Stoekl et al., Manchester University Press, 1985

External links


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См. также в других словарях:

  • Pineal gland — Pineal Pi ne*al, a. [L. pinea the cone of a pine, from pineus of the pine, from pinus a pine: cf. F. pin[ e]ale.] Of or pertaining to a pine cone; resembling a pine cone. [1913 Webster] {Pineal gland} (Anat.), a glandlike body in the roof of the… …   The Collaborative International Dictionary of English

  • pineal gland — a small, cone shaped endocrine organ in the posterior forebrain, secreting melatonin and involved in biorhythms and gonadal development. Also called epiphysis. See diag. under brain. [1705 15] * * * or pineal body Endocrine gland in the brain… …   Universalium

  • Pineal gland — A small gland located deep within in the brain. It is believed to secrete melatonin, and may therefore be part of the body’s sleep regulation apparatus. * * * pineal gland n a small body that arises from the roof of the third ventricle and is… …   Medical dictionary

  • pineal gland — pineal body a pea sized mass of nerve tissue attached by a stalk to the posterior wall of the third ventricle of the brain, deep between the cerebral hemispheres at the back of the skull. It functions as a gland, secreting the hormone melatonin.… …   The new mediacal dictionary

  • pineal gland — noun a small endocrine gland in the brain; situated beneath the back part of the corpus callosum; secretes melatonin • Syn: ↑pineal body, ↑epiphysis cerebri, ↑epiphysis • Hypernyms: ↑endocrine gland, ↑endocrine, ↑ductless gland …   Useful english dictionary

  • pineal gland — [ pɪnɪəl, pʌɪ ] (also pineal body) noun a pea sized conical mass of tissue behind the third ventricle of the brain, secreting a hormone like substance in some mammals. Origin C17: from Fr. pinéal, from L. pinea pine cone (with ref. to the shape… …   English new terms dictionary

  • pineal gland — noun Date: 1712 a small usually conical appendage of the brain of all craniate vertebrates that functions primarily as an endocrine organ and that in a few reptiles has the essential structure of an eye called also pineal, pineal body, pineal… …   New Collegiate Dictionary

  • pineal gland — noun /pʌɪˈniːəl ˌɡland/ A small, pinecone shaped endocrine gland found near the centre of the brain that produces melatonin. Syn: epiphysis, pineal body …   Wiktionary

  • pineal gland — /ˈpɪniəl glænd/ (say pineeuhl gland) noun an endocrine organ located in the midbrain, which secretes the hormone melatonin; epiphysis. Also, pineal body …   Australian-English dictionary

  • pineal gland — A tiny organ in the cerebrum that produces melatonin. Also called pineal body or pineal organ …   English dictionary of cancer terms


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