A) Tear gland/Lacrimal gland
B) Superior lacrimal punctum
C) Superior lacrimal canal lacrimation leads to tears
D) Tear sac/Lacrimal sac
E) Inferior lacrimal punctum
F) Inferior lacrimal canal
G) Nasolacrimal canal
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation (from Latin lacrima, meaning "tear") is the production or shedding of tears.
Strong emotions such as sorrow or elation, awe, pleasure, irritation of the eyes, laughing, and yawning may lead to an increased production of tears, or crying.
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Physiology [link]
In humans, the tear film coating the eye, known as the precorneal film, has three distinct layers, from the most outer surface:
| Name | Container(s) | Secretors | Functions |
|---|---|---|---|
| Lipid layer | oils | meibomian glands (or tarsal glands) | coats the aqueous layer; provides a hydrophobic barrier that envelopes tears and prevents their spilling onto the cheek. These glands are found among the tarsal plates. Thus, the tear fluid deposits between the eye proper and oil barriers of the lids.[1] |
| Aqueous layer | water and other substances such as proteins (e.g., tear lipocalin, lactoferrin, lysozyme[2] and lacritin) | lacrimal gland | promotes spreading of the tear film; promotes the control of infectious agents; promotes osmotic regulation |
| Mucous layer | mucin | conjunctival goblet cells | coats the cornea;provides a hydrophobic layer; allows for even distribution of the tear film; covers the cornea |
Having a thin tear film may prevent one's ability to wear contact lenses, as the amount of oxygen needed is higher than normal, and contact lenses stop oxygen from entering the eye. Eyes with thin tear film will dry out while wearing contact lenses. Special eye drops are available for contact lens wearers. Certain types of contact lenses are designed to let more oxygen through to the eye.
Drainage of tear film [link]
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The lacrimal glands secrete lacrimal fluid, which flows through the main excretory ducts into the space between the eyeball and lids. When the eyes blink, the lacrimal fluid is spread across the surface of the eye. Lacrimal fluid gathers in the lacrimal lake, and is drawn into the puncta by capillary action, then flows through the lacrimal canaliculi at the inner corner of the eyelids entering the lacrimal sac,[1] then on to the nasolacrimal duct, and finally into the nasal cavity. An excess of tears, as with strong emotion, can thus cause the nose to run. [1]
Types [link]
There are three very basic types of tears:
| Category | Description |
|---|---|
| Basal tears | In healthy mammalian eyes, the cornea is continually kept wet and nourished by basal tears. They lubricate the eye, and help to keep it clear of dust. Tear fluid contains water, mucin, lipids, lysozyme, lactoferrin, lipocalin, lacritin, immunoglobulins, glucose, urea, sodium, and potassium. Some of the substances in lacrimal fluid (such as lysozyme) fight against bacterial infection as a part of the immune system. Lysozyme does this by dissolving a layer in the outer coating, called peptidoglycan, of certain bacteria. It is a typical body fluid with a salt content similar to blood plasma. Usually, in a 24-hour period, 0.75 to 1.1 grams (0.03–0.04 ounce avoirdupois) of tears is secreted; this rate slows with age.[1] |
| Reflex tears | The second type of tears results from irritation of the eye by foreign particles, or from the presence of irritant substances such as onion vapors, tear gas, or pepper spray in the eye's environment, including the cornea, conjunctiva, or nasal mucosa. It can also occur with bright light and hot or peppery stimuli to the tongue and mouth. It is also linked with vomiting, coughing, and yawning.[1] These reflex tears attempt to wash out irritants that may have come into contact with the eye. |
| Crying or weeping (psychic tears) | The third category, in general, referred to as crying or weeping, is increased lacrimation due to strong emotional stress, anger, suffering, mourning, or physical pain. It does not occur during the brain's fight-or-flight response because the sympathetic nervous system inhibits lacrimation. This practice is not restricted to negative emotions; many people cry when extremely happy. In humans, emotional tears can be accompanied by reddening of the face and sobbing — cough-like, convulsive breathing, sometimes involving spasms of the whole upper body. Tears brought about by emotions have a different chemical make-up than those for lubrication; emotional tears contain more of the protein-based hormones prolactin, adrenocorticotropic hormone, and leucine enkephalin (a natural painkiller) than basal or reflex tears. The limbic system is involved in production of basic emotional drives, such as anger, fear, etc. The limbic system, to be specific, the hypothalamus, also has a degree of control over the autonomic system. The parasympathetic branch of the autonomic nervous system controls the lacrimal glands via the neurotransmitter acetylcholine through both the nicotinic and muscarinic receptors. When these receptors are activated, the lacrimal gland is stimulated to produce tears.[3] |
Neural Aspects [link]
The trigeminal V1 (fifth cranial) nerve bears the sensory pathway of the tear reflexes. When the trigeminal nerve is cut, tears from reflexes will stop, but not emotional tears. Likewise, application of cocaine to the surface of the eye, due to its paralyzing effect on the sensory nerve endings, inhibits the reflex even under exposure to strong tear gases. The motor pathway is autonomic (involuntary), and, in general, uses the pathway of the facial (seventh) nerve in the parasympathetic division. In parasympathetic imitators (such as acetylcholine), more tears are produced, and an anticholinergic drug like atropine inhibits tear production. A newborn infant has insufficient development of nervous control, so s/he "cries without weeping." If lacrimal gland malfunctions but does not cause any severe drying of the cornea, and the main lacrimal gland may be damaged in surgery or other failure of lacrimal function occur, it is not a serious matter, for the accessory glands are enough for general secretion. In reflex situations, copious tears are produced mainly in emergencies.[1]
Diseases and disorders [link]
Quality of vision is affected by the stability of the tear film.[4]
"Crocodile tears syndrome" is an uncommon consequence of nerve regeneration subsequent to Bell's palsy or other damage to the facial nerve in which efferent fibers from the superior salivary nucleus become improperly connected to nerve axons projecting to the lacrimal glands (tear ducts), causing one to shed tears (lacrimate) during salivation while smelling foods or eating. It is presumed that one would also salivate while crying due to the inverse improper connection of the lacrimal nucleus to the salivary glands, but this would be less noticeable.[5]
Keratoconjunctivitis sicca, known as dry eye, is a very common disorder of the tear film. However, sufferers can experience watering of the eyes, which is in fact a response to irritation caused by the original tear film deficiency.
Familial dysautonomia is a genetic condition that can be associated with a lack of overflow tears (alacrima) during emotional crying.[6]
Social aspects [link]
In nearly all cultures, crying is seen as a specific act associated with tears trickling down the cheeks and accompanied by characteristic sobbing sounds. Emotional triggers are most often sadness and grief, but crying can also be triggered by anger, happiness, fear, laughter or humor, frustration, remorse, or other strong, intense emotions. In many cultures, crying is associated with babies and children. Some cultures consider crying to be undignified and infantile, casting aspersions on those who cry publicly, except if it is due to the death of a close friend or relative. In most cultures, it is more socially acceptable for women and children to cry than men. In some Latin regions, crying among men is acceptable.[7][8][9]
Some modern therapy movements such as Re-evaluation Counseling teach that crying is beneficial to health and mental well-being, encouraging it positively.[10] An insincere display of grief or dishonest remorse is sometimes called crocodile tears in reference to an Ancient Greek anecdote that crocodiles would pretend to weep while luring or devouring their prey.[11] In addition, in medical terms, someone is said to have Crocodile tears syndrome as an uncommon consequence of recovery from Bell's palsy, in which faulty regeneration of the facial nerve causes sufferers to shed tears while eating.
Chemicals in Tears [link]
In a research conducted by the Weizmann Institute of Science in Rehovot, Israel, emotional tears from women have been found to reduce sexual arousal in men. Emotional tears are made up of a different chemical component than those evoked by eye irritants and can relay chemical messages to others.[12] The change in sex drive could be attributed to the drop in testosterone provoked by the chemicals in the tears meant to reduce aggression. In the animal world, it has been found that some blind mole rats would rub tears all over their bodies as a strategy to keep aggressive mole rats away.[13]
See also [link]
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Wikimedia Commons has media related to: Tears |
References [link]
- ^ a b c d e "eye, human."Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009
- ^ Ocular Pathology Study Guide: Tear Proteins
- ^ Skorucak A. "The Science of Tears." ScienceIQ.com. Accessed September 29, 2006.
- ^ Szczesna DH, Jaroński J, Kasprzak HT, Stenevi U (2006). "Interferometric measurements of dynamic changes of tear film". J Biomed Opt 11 (3): 34028. DOI:10.1117/1.2209881. PMID 16822077. https://link.aip.org/link/?jbo/11/34028&agg=MEDLINE_JBO.
- ^ Morais Pérez D, Dalmau Galofre J, Bernat Gili A, Ayerbe Torrero V (1990). "[Crocodile tears syndrome]" (in Spanish; Castilian). Acta Otorrinolaringol Esp 41 (3): 175–7. PMID 2261223.
- ^ Felicia B Axelrod and Gabrielle Gold-von Simson (October 3, 2007). "Hereditary sensory and autonomic neuropathies: types II, III, and IV". Orphanet Journal of Rare Diseases 2 (39): 39. DOI:10.1186/1750-1172-2-39. PMC 2098750. PMID 17915006. https://www.ojrd.com/content/2/1/39.
- ^ Dianne Hales (October 2005). "Big Boys Don't Cry — and Other Myths About Men and Their Emotions (page 2 of 3)". Reader's Digest. https://www.rd.com/living-healthy/big-boys-dont-cry----and-other-myths-about-men-and-their-emotions/article18053-1.html. Retrieved 2008-07-20.
- ^ Fran Metcalf (May 8, 2008). "These days it's OK for men to cry, say famous guys". The Courier Mail. https://www.news.com.au/couriermail/story/0,23739,23660131-23272,00.html. Retrieved 2008-07-20.[dead link]
- ^ John-Paul Flintoff (August 30, 2003). "Why we cry". The Age. https://www.theage.com.au/articles/2003/08/27/1061663846142.html. Retrieved 2008-07-20.
- ^ Re-evaluation Counseling site: "The Recovery Process"
- ^ World Wide Words: Crocodile tears
- ^ Weaver,Janelle. Crying Women Turn Men Off”. Scientific American Mind, May/June 2011, p. 22, 6.
- ^ Dell'Amore, Christine. " Women's Tears Reduce Sex Drive in Men, Study Hints", “National Geographic, January 6, 2011, accessed June 6, 2011.
External links [link]
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Wikiquote has a collection of quotations related to: Tears |
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Look up tears in Wiktionary, the free dictionary. |
- Nasolacrimal System Anatomy at eMedicine
- PERSONAL HEALTH : "University of Minnesota researchers who are studying the chemical composition of tears have recently isolated two important chemicals, leucine-enkephalin and prolactin, from emotional tears. The first of these may be an endorphin, one of the body's natural pain-relieving substances. — Both chemicals are found only in tears that are shed in response to emotion. Tears shed because of exposure to a cut onion would contain no such substance." By JANE E. BRODY, published February 22, 1984
https://wn.com/Tears
Instant Pleasure (album)
Instant Pleasure is Rockell's second album, released on October 10, 2000 on Robbins Entertainment. It is more pop oriented than her debut and was mostly produced by Tony Moran and Hex Hector. The album features the hit singles "What U Did 2 Me", "Tears" and "The Dance".
Track listing
Chart positions
Singles - Billboard (North America)
2112 (album)
2112 (pronounced "twenty-one twelve") is the fourth studio album by Canadian rock band Rush. Released on April 1, 1976, it features the seven-part title suite composed by Geddy Lee and Alex Lifeson, with lyrics written by Neil Peart telling a dystopian story set in the year 2112. It is sometimes described as a concept album although the songs on the second side are unrelated to the suite. Rush repeated this arrangement on the 1978 album Hemispheres.
2112 is one of two Rush albums listed in the book 1001 Albums You Must Hear Before You Die (the other being Moving Pictures). In 2006, a poll of Planet Rock listeners picked 2112 as the definitive Rush album. In 2012, it was ranked second on Rolling Stone's list of 'Your Favorite Prog Rock Albums of All Time', as voted for in a reader's poll, one of three Rush albums included (the others being Moving Pictures and Hemispheres).
A deluxe edition was released in 2012 as both a CD/DVD and a CD/Blu-ray. The CD featured the entire album remastered, as well as three live bonus tracks from their 1981 concert at Northlands Coliseum. The DVD and Blu-ray included the album in three different HD formats, as well as on-screen lyrics, liner notes, and a digital comic book depicting the story of the title track.
Tear
Tear may refer to:
People
Books and poetry
Games
Film
Music
Albums
Songs
Tears of wine
The phenomenon called tears of wine is manifested as a ring of clear liquid, near the top of a glass of wine, from which droplets continuously form and drop back into the wine. It is most readily observed in a wine which has a high alcohol content. It is also referred to as wine legs, curtains, or church windows.
Cause
The effect is a consequence of the fact that alcohol has a lower surface tension than water. If alcohol is mixed with water inhomogeneously, a region with a lower concentration of alcohol will pull on the surrounding fluid more strongly than a region with a higher alcohol concentration. The result is that the liquid tends to flow away from regions with higher alcohol concentration. This can be easily and strikingly demonstrated by spreading a thin film of water on a smooth surface and then allowing a drop of alcohol to fall on the center of the film. The liquid will rush out of the region where the drop of alcohol fell.
Wine is mostly a mixture of alcohol and water, with dissolved sugars, acids, colourants and flavourants. Where the surface of the wine meets the side of the glass, capillary action makes the liquid climb the side of the glass. As it does so, both alcohol and water evaporate from the rising film, but the alcohol evaporates faster, due to its higher vapor pressure. The resulting decrease in the concentration of alcohol causes the surface tension of the liquid to increase, and this causes more liquid to be drawn up from the bulk of the wine, which has a lower surface tension because of its higher alcohol content. The wine moves up the side of the glass and forms droplets that fall back under their own weight.
List of One Piece chapters (1–186)
One Piece is a shōnen manga series written and illustrated by Eiichiro Oda that has been translated into various languages and spawned a substantial media franchise. It follows the adventures of the seventeen-year-old boy Monkey D. Luffy, whose body gained the properties of rubber when he accidentally ate a supernatural fruit, as he travels the oceans in search of the series' titular treasure and gathers himself a ragtag crew of heroic pirates, named the Straw Hats. In Japan, the series is published by Shueisha – chapterwise in the manga anthology Weekly Shōnen Jump since the magazine's issue of August 4, 1997 and in tankōbon format since December 24, 1997.
In North America, Viz Media is publishing its English language adaptation of the series – chapterwise in the manga anthology Shonen Jump since the magazine's launch in November 2002 and in tankōbon format since June 2003. In the United Kingdom, the tankōbon were published by Gollancz Manga, starting March 2006, until Viz Media took over after the fourteenth volume. In Australia and New Zealand, the English volumes are distributed by Madman Entertainment since November 10, 2008.
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