Pineal gland

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Pineal gland
Pineal gland or epiphysis (in red)
Diagram of pituitary and pineal glands in the human brain
Details
PrecursorNeural ectoderm, roof of diencephalon
ArteryPosterior cerebral artery
Identifiers
Latinglandula pinealis
MeSHD010870
NeuroNames297
NeuroLex IDbirnlex_1184
TA98A11.2.00.001
TA23862
FMA62033
Anatomical terms of neuroanatomy

The pineal gland (also known as the pineal body[1] or epiphysis cerebri) is a small endocrine gland in the brain of most vertebrates. It produces melatonin, a serotonin-derived hormone, which modulates sleep patterns following the diurnal cycles.[2] The shape of the gland resembles a pine cone, which gives it its name.[3] The pineal gland is located in the epithalamus, near the center of the brain, between the two hemispheres, tucked in a groove where the two halves of the thalamus join.[4][5] It is one of the neuroendocrine secretory circumventricular organs in which capillaries are mostly permeable to solutes in the blood.[6]

The pineal gland is present in almost all vertebrates, but is absent in protochordates in which there is a simple pineal homologue. The hagfish, considered as a primitive vertebrate, has a rudimentary structure regarded as the "pineal equivalent" in the dorsal diencephalon.[7] In some species of amphibians and reptiles, the gland is linked to a light-sensing organ, variously called the parietal eye, the pineal eye or the third eye.[8] Reconstruction of the biological evolution pattern suggests that the pineal gland was originally a kind of atrophied photoreceptor that developed into a neuroendocrine organ.

Ancient Greeks were the first to notice the pineal gland and believed it to be a valve, a guardian for the flow of pneuma. Galen in the 2nd century C.E. could not find any functional role and regarded the gland as a structural support for the brain tissue. He gave the name konario, meaning cone or pinecone, which during Renaissance was translated to Latin as pinealis. The 17th century philosopher René Descartes regarded the gland as having a mystical purpose, describing it as the "principal seat of the soul". In the mid-20th century, the biological role as a neuroendocrine organ was established.[9]

  1. ^ Cite error: The named reference Chen_1998 was invoked but never defined (see the help page).
  2. ^ Reiter, R. J. (November 1991). "Neuroendocrine effects of light". International Journal of Biometeorology. 35 (3): 169–175. doi:10.1007/BF01049063. ISSN 0020-7128. PMID 1778647.
  3. ^ "Pineal (as an adjective)". Online Etymology Dictionary, Douglas Harper. 2018. Retrieved 27 October 2018.
  4. ^ Macchi MM, Bruce JN (2004). "Human pineal physiology and functional significance of melatonin". Frontiers in Neuroendocrinology. 25 (3–4): 177–195. doi:10.1016/j.yfrne.2004.08.001. PMID 15589268. S2CID 26142713.
  5. ^ Arendt J, Skene DJ (February 2005). "Melatonin as a chronobiotic". Sleep Medicine Reviews. 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, cortisol) to earlier (advance phase shift) or later (delay phase shift) times.
  6. ^ Gross PM, Weindl A (December 1987). "Peering through the windows of the brain". Journal of Cerebral Blood Flow and Metabolism. 7 (6): 663–672. doi:10.1038/jcbfm.1987.120. PMID 2891718. S2CID 18748366.
  7. ^ Ooka-Souda S, Kadota T, Kabasawa H (December 1993). "The preoptic nucleus: the probable location of the circadian pacemaker of the hagfish, Eptatretus burgeri". Neuroscience Letters. 164 (1–2): 33–36. doi:10.1016/0304-3940(93)90850-K. PMID 8152610. S2CID 40006945.
  8. ^ Eakin RM (1973). The Third Eye. Berkeley: University of California Press.
  9. ^ Lokhorst GJ (2018). Zalta EN (ed.). "Descartes and the Pineal Gland; In: The Stanford Encyclopedia of Philosophy" (Winter 2018 ed.). Metaphysics Research Lab, Stanford University. Retrieved 17 December 2019.