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Epiglottis

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Epiglottis
View of the larynx from behind. The epiglottis is the structure at the top of the image.
Details
PrecursorFourth pharyngeal arch[1]
FunctionPrevent food from entering the respiratory tract
Identifiers
Latinepiglottis
Greekἐπιγλωττίς
MeSHD004825
TA98A06.2.07.001
TA23190
FMA55130
Anatomical terminology

The epiglottis (pl.: epiglottises or epiglottides) is a leaf-shaped flap in the throat that prevents food and water from entering the trachea and the lungs. It stays open during breathing, allowing air into the larynx. During swallowing, it closes to prevent aspiration of food into the lungs, forcing the swallowed liquids or food to go along the esophagus toward the stomach instead. It is thus the valve that diverts passage to either the trachea or the esophagus.

The epiglottis is made of elastic cartilage covered with a mucous membrane, attached to the entrance of the larynx. It projects upwards and backwards behind the tongue and the hyoid bone.

The epiglottis may be inflamed in a condition called epiglottitis, which is most commonly due to the vaccine-preventable bacterium Haemophilus influenzae. Dysfunction may cause the inhalation of food, called aspiration, which may lead to pneumonia or airway obstruction. The epiglottis is also an important landmark for intubation.

The epiglottis has been identified as early as Aristotle, and gets its name from being above the glottis (epi- + glottis).

Structure

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Location of the epiglottis

The epiglottis sits at the entrance of the larynx. It is shaped like a leaf of purslane and has a free upper part that rests behind the tongue, and a lower stalk (Latin: petiolus).[2] The stalk originates from the back surface of the thyroid cartilage, connected by a thyroepiglottic ligament. At the sides, the stalk is connected to the arytenoid cartilages at the walls of the larynx by folds.[2]

The epiglottis originates at the entrance of the larynx, and is attached to the hyoid bone. From there, it projects upwards and backwards behind the tongue.[3] The space between the epiglottis and the tongue is called the vallecula.[3]

Microanatomy

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The epiglottis has two surfaces; a forward-facing anterior surface, and a posterior surface facing the larynx.[2] The forward-facing surface is covered with several layers of thin cells (stratified squamous epithelium), and is not covered with keratin, the same surface as the back of the tongue.[2] The back surface is covered in a layer of column-shaped cells with cilia, similar to the rest of the respiratory tract. It also has mucus-secreting goblet cells.[2] There is an intermediate zone between these surfaces that contains cells that transition in shape.[4] The body of the epiglottis consists of elastic cartilage.[2]

Development

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The epiglottis arises from the fourth pharyngeal arch. It can be seen as a distinct structure later than the other cartilage of the pharynx, visible around the fifth month of development.[1] The position of the epiglottis also changes with ageing. In infants, it touches the soft palate, whereas in adults, its position is lower.[3]

Variation

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A high rising epiglottis (with forward-facing anterior surface being visible)

A high-rising epiglottis is a normal anatomical variation, visible during an examination of the mouth. It does not cause any serious problem apart from maybe a mild sensation of a foreign body in the throat. It is seen more often in children than adults and does not need any medical or surgical intervention.[5] The front surface of the epiglottis is occasionally notched.[2]

Function

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The epiglottis is normally pointed upward during breathing with its underside functioning as part of the pharynx.[2] There are taste buds on the epiglottis.[6]

Swallowing

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During swallowing, the epiglottis bends backwards, folding over the entrance to the trachea, and preventing food from going into it.[2] The folding backwards is a complex movement the causes of which are not completely understood.[2] It is likely that during swallowing the hyoid bone and the larynx move upwards and forwards, which increases passive pressure from the back of the tongue; the aryepiglottic muscles contract; the passive weight of the food pushes down; and the laryngeal and thyroarytenoid muscles contract.[2] The consequence of this is that during swallowing the bent epiglottis blocks off the trachea, preventing food from going into it; food instead travels down the esophagus, which is behind it.[3]

Speech sounds

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In many languages, the epiglottis is not essential for producing sounds.[2] In some languages, the epiglottis is used to produce epiglottal consonant speech sounds, though this sound-type is rather rare.[7]

Clinical significance

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Inflammation

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Main article: Epiglottitis

Inflammation of the epiglottis is known as epiglottitis. Epiglottitis is mainly caused by Haemophilus influenzae. A person with epiglottitis may have a fever, sore throat, difficulty swallowing, and difficulty breathing. For this reason, acute epiglottitis is considered a medical emergency, because of the risk of obstruction of the pharynx. Epiglottitis is often managed with antibiotics, inhaled aerosolised epinephrine to act as a bronchodilator, and may require tracheal intubation or a tracheostomy if breathing is difficult.[8]

The incidence of epiglottitis has decreased significantly in countries where vaccination against Haemophilus influenzae is administered.[9][10]

Aspiration

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When food or other objects travel down the respiratory tract rather than down the esophagus to the stomach, this is called aspiration. This can lead to the obstruction of airways, inflammation of lung tissue, and aspiration pneumonia; and in the long term, atelectasis and bronchiectasis.[3] One reason aspiration can occur is because of failure of the epiglottis to close completely.[2][3]

If food or liquid enters the airway due to the epiglottis failing to close properly, throat-clearing or a cough reflex may occur to protect the respiratory system and expel material from the airway.[3][11] Where there is impairment in laryngeal vestibule sensation, silent aspiration (entry of material to the airway that does not result in a cough reflex) may occur.[3][12]

Other

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The epiglottis and vallecula are important anatomical landmarks in intubation.[13] Abnormal positioning of the epiglottis is a rare cause of obstructive sleep apnoea.[14]

Other animals

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The epiglottis is present in mammals,[15] including land mammals and cetaceans,[16] also as a cartilaginous structure.[17] Like in humans, it functions to prevent entry of food into the trachea during swallowing.[17] The position of the larynx is flat in mice and other rodents, as well as rabbits.[4] For this reason, because the epiglottis is located behind the soft palate in rabbits, they are obligate nose breathers,[18][19] as are mice and other rodents.[4] In rodents and mice, there is a unique pouch in front of the epiglottis, and the epiglottis is commonly injured by inhaled substances, particularly at the transition zone between the flattened and cuboidal epithelium.[20][4] It is also common to see taste buds on the epiglottis in these species.[4]

History

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The epiglottis was noted by Aristotle,[15] although the epiglottis' function was first defined by Vesalius in 1543.[21] The word has Greek roots.[22] The epiglottis gets its name from being above (Ancient Greek: ἐπί, romanized: epi-) the glottis (Ancient Greek: γλωττίς, romanized: glottis, lit. 'tongue').[23]

Additional images

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  • Cross-section of the larynx, with structures including the epiglottis labelled.
    Cross-section of the larynx, with structures including the epiglottis labelled.
  • Cross-section of the larynx of a horse. The epiglottis here is shown as '2'.
    Cross-section of the larynx of a horse. The epiglottis here is shown as '2'.
  • Structures of the larynx as viewed during laryngoscopy. The leaf-like epiglottis is shown as number '3'. Other structures: 1=vocal folds, 2=vestibular fold, 3=epiglottis, 4=plica aryepiglottica, 5=arytenoid cartilage, 6=sinus piriformis, 7=dorsum of the tongue
    Structures of the larynx as viewed during laryngoscopy. The leaf-like epiglottis is shown as number '3'. Other structures: 1=vocal folds, 2=vestibular fold, 3=epiglottis, 4=plica aryepiglottica, 5=arytenoid cartilage, 6=sinus piriformis, 7=dorsum of the tongue

See also

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This article uses anatomical terminology.

References

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  1. ^ a b Schoenwolf, Gary C.; et al. (2009). ""Development of the Urogenital system"". Larsen's human embryology (4th ed., Thoroughly rev. and updated. ed.). Philadelphia: Churchill Livingstone/Elsevier. p. 362. ISBN 9780443068119.
  2. ^ a b c d e f g h i j k l m Standring, Susan, ed. (2016). Gray's anatomy : the anatomical basis of clinical practice (41st ed.). Philadelphia. pp. 586–8. ISBN 9780702052309. OCLC 920806541.{{cite book}}: CS1 maint: location missing publisher (link)
  3. ^ a b c d e f g h Matsuo, Koichiro; Palmer, Jeffrey B. (November 2008). "Anatomy and Physiology of Feeding and Swallowing – Normal and Abnormal". Physical Medicine and Rehabilitation Clinics of North America. 19 (4): 691–707. doi:10.1016/j.pmr.2008.06.001. ISSN 1047-9651. PMC 2597750. PMID 18940636.
  4. ^ a b c d e Harkema, Jack R.; Carey, Stephan A.; Wagner, James G.; Dintzis, Suzanne M.; Liggitt, Denny (2018), "Nose, Sinus, Pharynx, and Larynx", Comparative Anatomy and Histology, Elsevier, pp. 89–114, doi:10.1016/b978-0-12-802900-8.00006-3, ISBN 9780128029008
  5. ^ Petkar N, Georgalas C, Bhattacharyya A (2007). "High-rising epiglottis in children: should it cause concern?". J Am Board Fam Med. 20 (5): 495–6. doi:10.3122/jabfm.2007.05.060212. PMID 17823468.
  6. ^ Jowett, Adrian; Shrestha, Rajani (November 1998). "Mucosa and taste buds of the human epiglottis". Journal of Anatomy. 193 (4): 617–618. doi:10.1046/j.1469-7580.1998.19340617.x. PMC 1467887. PMID 10029195.
  7. ^ Shahin, Kimary (2011), "Pharyngeals", The Blackwell Companion to Phonology, American Cancer Society, pp. 1–24, doi:10.1002/9781444335262.wbctp0025, ISBN 9781444335262
  8. ^ Nicki R. Colledge; Brian R. Walker; Stuart H. Ralston, eds. (2010). Davidson's principles and practice of medicine. illustrated by Robert Britton (21st ed.). Edinburgh: Churchill Livingstone/Elsevier. p. 681. ISBN 978-0-7020-3084-0.
  9. ^ Reilly BK, Reddy SK, Verghese ST (April 2013). "Acute epiglottitis in the era of post-Haemophilus influenzae type B (HIB) vaccine". J Anesth. 27 (2): 316–7. doi:10.1007/s00540-012-1500-9. PMID 23076559. S2CID 33540359.
  10. ^ Hermansen MN, Schmidt JH, Krug AH, Larsen K, Kristensen S (April 2014). "Low incidence of children with acute epiglottis after introduction of vaccination". Dan Med J. 61 (4): A4788. PMID 24814584.
  11. ^ Widdicombe, J. (1 July 2006). "Cough: what's in a name?". European Respiratory Journal. 28 (1): 10–15. doi:10.1183/09031936.06.00096905. PMID 16816346.
  12. ^ Ramsey, Deborah; Smithard, David; Kalra, Lalit (13 December 2005). "Silent Aspiration: What Do We Know?". Dysphagia. 20 (3): 218–225. doi:10.1007/s00455-005-0018-9. PMID 16362510. S2CID 24880995.
  13. ^ Peitzman, Andrew B.; Rhodes, Michael; Schwab, C. William (2008). The Trauma Manual: Trauma and Acute Care Surgery. Lippincott Williams & Wilkins. p. 86. ISBN 9780781762755.
  14. ^ Catalfumo, Frank J.; Golz, Avishay; Westerman, S. Thomas; Gilbert, Liane M.; Joachims, Henry Z.; Goldenberg, David (2018). "The epiglottis and obstructive sleep apnoea syndrome". The Journal of Laryngology & Otology. 112 (10): 940–943. doi:10.1017/S0022215100142136. ISSN 0022-2151. PMID 10211216. S2CID 23615987.
  15. ^ a b Leroi, Armand Marie (2014-08-28). The Lagoon: How Aristotle Invented Science. Bloomsbury Publishing. p. 145. ISBN 9781408836217.
  16. ^ Perrin, William F.; Würsig, Bernd; Thewissen, J. G. M. (2009-02-26). Encyclopedia of Marine Mammals. Academic Press. p. 225. ISBN 9780080919935.
  17. ^ a b Colville, Thomas P.; Bassert, Joanna M. (2008). Clinical Anatomy and Physiology for Veterinary Technicians. Mosby Elsevier. p. 251. ISBN 9780323046855.[permanent dead link‍]
  18. ^ Suckow, Mark A.; Stevens, Karla A.; Wilson, Ronald P. (2012-01-23). The Laboratory Rabbit, Guinea Pig, Hamster, and Other Rodents. Academic Press. p. 209. ISBN 9780123809209.
  19. ^ Johnson-Delaney, Cathy A.; Orosz, Susan E. (2011). "Rabbit Respiratory System: Clinical Anatomy, Physiology and Disease". Veterinary Clinics of North America: Exotic Animal Practice. 14 (2): 257–266. doi:10.1016/j.cvex.2011.03.002. PMID 21601814.
  20. ^ Treuting, Piper M.; Dintzis, Suzanne M.; Montine, Kathleen S. (2017-08-29). Comparative Anatomy and Histology: A Mouse, Rat, and Human Atlas. Academic Press. pp. 109–110. ISBN 9780128029190.
  21. ^ Issues in Anatomy, Physiology, Metabolism, Morphology, and Human Biology: 2011 Edition. ScholarlyEditions. 2012-01-09. p. 202. ISBN 9781464964770.
  22. ^ Lydiatt DD, Bucher GS (March 2010). "The historical Latin and etymology of selected anatomical terms of the larynx". Clin Anat. 23 (2): 131–44. doi:10.1002/ca.20912. PMID 20069644. S2CID 10234119.
  23. ^ Harper, Douglas. "epiglottis | Origin and meaning of epiglottis by Online Etymology Dictionary". www.etymonline.com. Retrieved 26 October 2019.
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