Epiglottis
Template:Short description Template:Good article Template:Infobox anatomy The epiglottis (Template:Plural form: 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).
StructureEdit
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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 (Template:Langx).<ref name=Grays2016>Template:Cite book</ref> 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.<ref name=Grays2016 />
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.<ref name=":0">Template:Cite journal</ref> The space between the epiglottis and the tongue is called the vallecula.<ref name=":0" />
MicroanatomyEdit
The epiglottis has two surfaces; a forward-facing Template:Wt surface, and a Template:Wt surface facing the larynx.<ref name=Grays2016 /> 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.<ref name=Grays2016 /> 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.<ref name=Grays2016 /> There is an intermediate zone between these surfaces that contains cells that transition in shape.<ref name=":3">Template:Citation</ref> The body of the epiglottis consists of elastic cartilage.<ref name=Grays2016 />
DevelopmentEdit
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.<ref name=Schoenwolf2009>Template:Cite book</ref> The position of the epiglottis also changes with ageing. In infants, it touches the soft palate, whereas in adults, its position is lower.<ref name=":0" />
VariationEdit
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.<ref name="pmid17823468">Template:Cite journal</ref> The front surface of the epiglottis is occasionally notched.<ref name=Grays2016 />
FunctionEdit
The epiglottis is normally pointed upward during breathing with its underside functioning as part of the pharynx.<ref name=Grays2016/> There are taste buds on the epiglottis.<ref name="pmid10029195">Template:Cite journal</ref>
SwallowingEdit
During swallowing, the epiglottis bends backwards, folding over the entrance to the trachea, and preventing food from going into it.<ref name=Grays2016 /> The folding backwards is a complex movement the causes of which are not completely understood.<ref name=Grays2016 /> 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.<ref name=Grays2016 /> 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.<ref name=":0" />
Speech soundsEdit
In many languages, the epiglottis is not essential for producing sounds.<ref name=Grays2016 /> In some languages, the epiglottis is used to produce epiglottal consonant speech sounds, though this sound-type is rather rare.<ref>Template:Citation</ref>
Clinical significanceEdit
InflammationEdit
The 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.<ref name=DAVIDSONS2010>Template:Cite book</ref>
The incidence of epiglottitis has decreased significantly in countries where vaccination against Haemophilus influenzae is administered.<ref name="pmid23076559">Template:Cite journal</ref><ref name="pmid24814584">Template:Cite journal</ref>
AspirationEdit
When food or other objects travel down the respiratory tract rather than down the esophagus to the stomach, this is called Template:Wt. This can lead to the obstruction of airways, inflammation of lung tissue, and aspiration pneumonia; and in the long term, atelectasis and bronchiectasis.<ref name=":0" /> One reason aspiration can occur is because of failure of the epiglottis to close completely.<ref name=Grays2016 /><ref name=":0" />
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.<ref name=":0" /><ref>Template:Cite journal</ref> 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.<ref name=":0" /><ref>Template:Cite journal</ref>
OtherEdit
The epiglottis and vallecula are important anatomical landmarks in intubation.<ref>Template:Cite book</ref> Abnormal positioning of the epiglottis is a rare cause of obstructive sleep apnoea.<ref>Template:Cite journal</ref>
Other animalsEdit
The epiglottis is present in mammals,<ref name=":1">Template:Cite book</ref> including land mammals and cetaceans,<ref>Template:Cite book</ref> also as a cartilaginous structure.<ref name=":2">Template:Cite bookTemplate:Dead link</ref> Like in humans, it functions to prevent entry of food into the trachea during swallowing.<ref name=":2" /> The position of the larynx is flat in mice and other rodents, as well as rabbits.<ref name=":3" /> For this reason, because the epiglottis is located behind the soft palate in rabbits, they are obligate nose breathers,<ref>Template:Cite book</ref><ref>Template:Cite journal</ref> as are mice and other rodents.<ref name=":3" /> 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.<ref>Template:Cite book</ref><ref name=":3" /> It is also common to see taste buds on the epiglottis in these species.<ref name=":3" />
HistoryEdit
The epiglottis was noted by Aristotle,<ref name=":1" /> although the epiglottis' function was first defined by Vesalius in 1543.<ref>Template:Cite book</ref> The word has Greek roots.<ref name="pmid20069644">Template:Cite journal</ref> The epiglottis gets its name from being above (Template:Langx) the glottis (Template:Langx).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Additional imagesEdit
- Illu larynx.jpg
Cross-section of the larynx, with structures including the epiglottis labelled.
- Kehlkopf Pferd.jpg
Cross-section of the larynx of a horse. The epiglottis here is shown as '2'.
- Larynx normal.jpg
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 alsoEdit
ReferencesEdit
External linksEdit
- Template:NormanAnatomy (Template:NormanAnatomyFig)
- Where is the Epiglottis? Template:Webarchive at Study Sciences