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The epiglottis 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 Swallowing, sometimes called deglutition in scientific contexts, is the process in the human or animal body that allows for a substance to pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. Swallowing is ...
, it closes to prevent aspiration of food into the lungs, forcing the swallowed liquids or food to go along the
oesophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
toward the stomach instead. It is thus the valve that diverts passage to either the trachea or the oesophagus. The epiglottis is made of
elastic cartilage Elastic cartilage, fibroelastic cartilage or yellow fibrocartilage is a type of cartilage present in the pinnae (auricles) of the ear giving it shape, provides shape for the lateral region of the external auditory meatus, medial part of the audit ...
covered with a
mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...
, attached to the entrance of the larynx. It projects upwards and backwards behind the
tongue The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste b ...
and the
hyoid bone The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical ver ...
. The epiglottis may be inflamed in a condition called epiglottitis, which is most commonly due to the vaccine-preventable bacteria '' 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

The epiglottis sits at the entrance of the larynx. It is shaped like a leaf of
purslane Purslane is a common name for several mostly unrelated plants with edible leaves and may refer to: * Portulacaceae, a family of succulent flowering plants, and especially: ** ''Portulaca oleracea'', a species of ''Portulaca'' eaten as a leaf vegeta ...
and has a free upper part that rests behind the tongue, and a lower stalk ( la, petiolus). The stalk originates from the back surface of the
thyroid cartilage The thyroid cartilage is the largest of the nine cartilages that make up the ''laryngeal skeleton'', the cartilage structure in and around the trachea that contains the larynx. It does not completely encircle the larynx (only the cricoid cartilage ...
, connected by a
thyroepiglottic ligament The thyroepiglottic ligament is an intrinsic ligament of the larynx. It connects the stalk of the epiglottis to the angle formed by the two laminæ of the thyroid cartilage The thyroid cartilage is the largest of the nine cartilages that make up t ...
. At the sides, the stalk is connected to the
arytenoid cartilage The arytenoid cartilages () are a pair of small three-sided pyramids which form part of the larynx. They are the site of attachment of the vocal cords. Each is pyramidal or ladle-shaped and has three surfaces, a base, and an apex. The arytenoid ...
s at the walls of the larynx by folds. 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 The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste b ...
. The space between the epiglottis and the tongue is called the vallecula.


Microanatomy

The epiglottis has two surfaces; a forward-facing surface, and a surface facing the larynx. 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. 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 mucous-secreting
goblet cells Goblet cells are simple columnar epithelial cells that secrete gel-forming mucins, like mucin 5AC. The goblet cells mainly use the merocrine method of secretion, secreting vesicles into a duct, but may use apocrine methods, budding off their sec ...
. There is an intermediate zone between these surfaces that contains cells that transition in shape. The body of the epiglottis consists of
elastic cartilage Elastic cartilage, fibroelastic cartilage or yellow fibrocartilage is a type of cartilage present in the pinnae (auricles) of the ear giving it shape, provides shape for the lateral region of the external auditory meatus, medial part of the audit ...
.


Development

The epiglottis arises from the fourth
pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arch ...
. It can be seen as a distinct structure later than the other cartilage of the pharynx, visible around the fifth month of development. The position of the epiglottis also changes with ageing. In infants, it touches the soft palate, whereas in adults, its position is lower.


Variation

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. The front surface of the epiglottis is occasionally notched.


Function

The epiglottis is normally pointed upward during
breathing Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen. All aerobic creatures need oxygen for cellula ...
with its underside functioning as part of the pharynx. There are taste buds on the epiglottis.


Swallowing

During
swallowing Swallowing, sometimes called deglutition in scientific contexts, is the process in the human or animal body that allows for a substance to pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. Swallowing is ...
, the epiglottis bends backwards, folding over the entrance to the trachea, and preventing food from going into it. The folding backwards is a complex movement the causes of which are not completely understood. It is likely that during swallowing the
hyoid bone The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical ver ...
and the larynx move upwards and forwards, which increases passive pressure from the back of the tongue; because the
aryepiglottic muscle The aryepiglottic muscle, or aryepiglotticus muscle is an intrinsic muscle of the larynx. The muscle originates from the muscular process of arytenoid cartilage and inserts to the aryepiglottic fold and lateral border of epiglottis. The aryepigl ...
s contract; because of the passive weight of the food pushing down; and because of contraction of laryngeal and because of contraction of thyroarytenoid muscles. 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.


Speech sounds

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


Clinical significance


Inflammation

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
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...
s, inhaled aerosolised
epinephrine Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...
to act as a
bronchodilator A bronchodilator or broncholytic (although the latter occasionally includes secretory inhibition as well) is a substance that dilates the bronchi and bronchioles, decreasing resistance in the respiratory airway and increasing airflow to the lung ...
, and may require
tracheal intubation Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic tube into the trachea (windpipe) to maintain an open airway or to serve as a conduit through which to administer certain drugs. It is frequently ...
or a
tracheostomy Tracheotomy (, ), or tracheostomy, is a surgical airway management procedure which consists of making an incision (cut) on the anterior aspect (front) of the neck and opening a direct airway through an incision in the trachea (windpipe). The re ...
if breathing is difficult. The incidence of epiglottitis has decreased significantly in countries where vaccination against ''Haemophilus influenzae'' is administered.


Aspiration

When food or other objects travel down the respiratory tract rather than down the esophagus to the stomach, this is called . This can lead to airway obstruction, inflammation of lung tissue, and
aspiration pneumonia Aspiration pneumonia is a type of lung infection that is due to a relatively large amount of material from the stomach or mouth entering the lungs. Signs and symptoms often include fever and cough of relatively rapid onset. Complications may inclu ...
; and in the long term, atelectasis and
bronchiectasis Bronchiectasis is a disease in which there is permanent enlargement of parts of the airways of the lung. Symptoms typically include a chronic cough with mucus production. Other symptoms include shortness of breath, coughing up blood, and chest ...
. One reason aspiration can occur is because of failure of the epiglottis to close completely. Should food or liquid enter the airway due to the epiglottis failing to close properly, throat clearing or the cough reflex may occur to protect the respiratory system and expel material from the airway. 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.


Other

The epiglottis and vallecula are important anatomical landmarks in intubation. Abnormal positioning of the epiglottis is a rare cause of
obstructive sleep apnoea Obstructive sleep apnea (OSA) is the most common sleep-related breathing disorder and is characterized by recurrent episodes of complete or partial obstruction of the upper airway leading to reduced or absent breathing during sleep. These episod ...
.


Other animals

The epiglottis is present in mammals, including land mammals and
cetaceans Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...
, also as a cartilaginous structure. Like in humans, it functions to prevent entry of food into the trachea during swallowing. The position of the larynx is flat in mice and other rodents, as well as rabbits. For this reason, because the epiglottis is located behind the soft palate in rabbits, they are obligate nose breathers, as are mice and other rodents. 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. It is also common to see taste buds on the epiglottis in these species.


History

The epiglottis was noted by Aristotle, although the epiglottis' function was first defined by Vesalius in 1543. The word has Greek roots. The epiglottis gets its name from being above ( grc, ἐπί, translit=epi-) the glottis ( grc, γλωττίς, translit=glottis, lit=tongue).


Additional images

File:Illu larynx.jpg, Cross-section of the larynx, with structures including the epiglottis labelled. File:Kehlkopf Pferd.jpg, Cross-section of the larynx of a horse. The epiglottis here is shown as '2'. File: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 also

* Epiglottal consonant *
Epiglotto-pharyngeal consonant A pharyngeal consonant is a consonant that is articulated primarily in the pharynx. Some phoneticians distinguish upper pharyngeal consonants, or "high" pharyngeals, pronounced by retracting the root of the tongue in the mid to upper pharynx, ...
*
Pharyngeal consonant A pharyngeal consonant is a consonant that is articulated primarily in the pharynx. Some phoneticians distinguish upper pharyngeal consonants, or "high" pharyngeals, pronounced by retracting the root of the tongue in the mid to upper pharynx, ...


References


External links

* ()
Where is the Epiglottis?
at Study Sciences {{Authority control Digestive system Larynx Human throat