History of the pineal gland
From Wikipedia, the free encyclopedia
The history of the pineal gland is an account of the scientific development on the understanding of the pineal gland from the ancient Greeks that led to the discovery of its neuroendocrine properties in the 20th century CE. As an elusive and unique part of the brain, the pineal gland has the longest history among the body organs as a structure of unknown function – it took almost two millennia to discover its biological roles.[1] Until the 20th century, it was recognised with a mixture of mysticism and scientific conjectures as to its possible nature.[2][3]
The ancient Greeks visualised the pineal gland as a sort of guard (valve), like the pylorus of stomach, that regulate the flow of pneuma (vital spirits) in the brain. Galen of Pergamum in the 2nd century CE was the first to make written record of the gland and argued against the prevailing concept. According to him, the gland has no spiritual or physiological role, but merely a supporting organ of the brain, and gave the name κωνάριο (konario, often Latinised as conarium) for its cone-shaped appearance.[4] Galen's description remained a scientific concept until the Renaissance when alternative explanations were postulated. By then, the Latin name glandula pinealis had become a common usage. René Descartes's description as the "seat of the soul" in the 17th century became one of the most influential concepts for the next three centuries.
The biological role of the pineal gland was first discovered in 1958 when dermatologist Aaron B. Lerner and colleagues discovered a skin-lightening factor, which they named melatonin. Lerner's team found the chemical compound from the cow pineal extract that could lightens the skin of frog. It was subsequently discovered that melatonin is a hormone that regulates day-night cycle (circadian rhythm), and modulates other organs. The pineal gland thereby was established as an endocrine gland. As it controls the other important endocrine glands—including the so-called "master gland", the pituitary gland—it is more appropriate to refer the pineal gland as the true "master gland" of the body.[5][6][7]
English
The English term "pineal" first became in use in the 1680s and is from Middle French pinéal, which is from Latin pinea (conifer cone) in reference to the gland's similar shape.[8][9][10] The English noun "gland" is derived from the Old French word glandre, meaning "gland", ultimately derived from the Latin glandula.
Latin
The Latin term glandula, "little acorn"; is derived from glāns, a term for anything acorn shaped e.g., an acorn, nut, acorn-shaped fruit, an acord-shaped ball of lead or clay hurled at the enemy, or the glans of the penis, also having the ula diminutive ending. Glāns is from Proto-Italic *glānts, from Proto-Indo-European *gʷelh₂- “acorn”.[11][12]
The Latin pinea, "pinecone"; "Pine Nut";[13] is an inflected form of pīneus, "pine"; "pinelike";[14] which is derived from pīnus “pine” + -eus, "pine tree", "fir tree"; "pinewood"; "a thing made of such wood"; "lance", "spear"; "wreath of pine leaves"; "pine forest, pineland". Pīnus is from Proto-Italic *pīnos, of disputed origin, with multiple theories proposed:
- From the same origin as Ancient Greek πῐ́νᾰξ (pĭ́năx, “wooden board", "plank”).
- From the same origin as Ancient Greek πίτῠς (pítŭs, “pine tree”) and Albanian pishë “id”, which is generally reconstructed as Proto-Indo-European *pī́ts.
- Sanskrit पितु pitu: “sap", "juice", "resin”.[15][16]
Cerebrī is the genitive singular of cerebrum, "brain"; "skull"; "upper pith". From Proto-Italic *kerazrom, from Proto-Indo-European *ḱerh₂srom, ultimately from Proto-Indo-European *ḱerh₂-. Compare Ancient Greek κᾰ́ρᾱ (kắrā, “a head, face”).[17]
Greek
κωνάριο is the diminutive of ancient Greek κῶνος kônos = "cone"; "pine-cone"; "peak"; "cone-shaped object"; The suffix -άριον (-arion) is a standard late Koine diminutive, so κων-άριον is literally = "little cone". κῶνος itself is inherited Indo-European. It’s cognate with:
- Latin cōnus "cone"; borrowed from Greek
- Sanskrit शंकु śaṅku "peg, spike"
- Old Norse hann "stone"
- Ultimately all derived from Proto-Indo-European PIE root *ḱeh₃- or *ḱōnos "sharp point"; "cone".[18][19]
ἐπίφυσις epīphysis = ἐπί "upon"; "on" + φύσις "growth"; "nature"; from φύω "to grow"; "bring forth". So literally "growing upon"; "outgrowth".
PIE roots:
- ἐπί < PIE *h₁epi "on, at, near"
- φύω < PIE *bʰuH- "to become", "grow", "be", "bring forth by nature".[20][21]
Ancient Greek κωνάριον (kōnárion), is a diminutive of κῶνος (kônos), “pine cone"; "pine nut”. Galen named the gland κωνάριο, kōnário; in the 2nd century C.E. in the book On the Usefulness of the Parts of the Body; Περὶ χρείας μορίων; De usu partium.[22] Epiphysis Cerebri is greek-latin neologism first being used around 1625-35.[23] Neither in the ancient greek nor latin corpuses is the pineal gland referred to as ἐπίφυσις epīphysis or epiphysis cerebri.[24][25][26][27][28] In the Hippocratic corpus, ἐπίφυσις refers to the end of a long bone.[29]
Ancient Greeks
Greek physician Galen was the first to give written description about the pineal gland in the 2nd century CE.[30] He indicated that the structure as a part of the brain was already known to earlier Greek scholars, crediting Herophilus (325–280 BCE) as the first to have described the possible role of the gland.[31] Herophilus had explained that the structure was a kind of valve, like the pylorus of stomach that controls the amount of food particles moving into the intestine. As a valve in the brain, the structure guards the brain chambers and maintains the right amount of the flow of vital spirits called pneuma. It was conceived as a guardian or housekeeper that regulates the movement of vital spirits from the middle (now identified to be the third) ventricle to the one in the parencephalis (fourth ventricle).[32] The idea was generally endorsed by other Greek scholars.[33]
Galen made the description of the pineal gland in his two books De usu partium corporis humani, libri VII (On the Usefulness of Parts of the Body, Part 8) and De anatomicis administrationibus, libri IX (On Anatomical Procedures, Part 9).[34] In De usu partium corporis humani, he gave the name κωνάριο (konario, often Latinised as conarium) meaning a cone, as in pinecone.[4] He correctly identified the structure and the position of the gland as directly lying behind the third ventricle. He opposed the prevailing concept originated by Herophilus and instead upheld that the organ could not be a brain valve for two basic reasons: it is located outside of the brain tissue and it does not move on its own.[30][35]
Galen did believe that the brain has a valve for movements of the vital spirits and identified the valve as a worm-like structure in the cerebellum (vermis, for worm, later called vermiform epiphysis, known today as the vermis cerebelli or cerebellar vermis).[36][37] In his attempt to understand the function of the gland, he traced the surrounding blood vessels from which he identified the great vein of the cerebellum, later called the vein of Galen.[4][38] Failing to discover the function, he believed that the pineal gland was merely a structural support for the cerebral veins.[39]