The epiglottis (: epiglottises or epiglottides) is a leaf-shaped flap in the

throat In vertebrate anatomy, the throat is the front part of the neck, internally positioned in front of the vertebrae. It contains the Human pharynx, pharynx and larynx. An important section of it is the epiglottis, separating the esophagus from the t ...

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 The esophagus (American English), oesophagus (British English), or œsophagus (Œ, archaic spelling) (American and British English spelling differences#ae and oe, see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), c ...

toward the stomach instead. It is thus the valve that diverts passage to either the

trachea The trachea (: tracheae or tracheas), also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all animals' lungs. The trachea extends from ...

or the esophagus. The epiglottis is made of elastic cartilage 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 ...

, attached to the entrance of the

larynx The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...

. It projects upwards and backwards behind the

tongue The tongue is a Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...

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 verte ...

. The epiglottis may be inflamed in a condition called epiglottitis, which is most commonly due to the vaccine-preventable bacterium ''

Haemophilus influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative, Motility, non-motile, Coccobacillus, coccobacillary, facultative anaerobic organism, facultatively anaerobic, Capnophile, capnophili ...

''. Dysfunction may cause the inhalation of food, called aspiration, which may lead to

pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...

or airway obstruction. The epiglottis is also an important landmark for

intubation Intubation (sometimes entubation) is a medical procedure involving the insertion of a tube into the body. Most commonly, intubation refers to tracheal intubation, a procedure during which an endotracheal tube is inserted into the trachea to supp ...

. The epiglottis has been identified as early as Aristotle, and gets its name from being above the

glottis The glottis (: glottises or glottides) is the opening between the vocal folds (the rima glottidis). The glottis is crucial in producing sound from the vocal folds. Etymology From Ancient Greek ''γλωττίς'' (glōttís), derived from ''γ ...

('' epi-'' + ''glottis'').

Structure

The epiglottis sits at the entrance of the

. It is shaped like a leaf of purslane and has a free upper part that rests behind the tongue, and a lower stalk (). 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. The epiglottis originates at the entrance of the

, and is attached to the hyoid bone. From there, it projects upwards and backwards behind the

. 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 A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural ...

), 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 The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

, similar to the rest of the

respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respirato ...

. It also has

mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...

-secreting goblet cells. There is an intermediate zone between these surfaces that contains cells that transition in shape. The body of the epiglottis consists of elastic cartilage.

Development

The epiglottis arises from the fourth

pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are transient structures seen in the Animal embryonic development, embryonic development of humans and other vertebrates, that are recognisable precursors for many structures. In fish, t ...

. 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 The soft palate (also known as the velum, palatal velum, or muscular palate) is, in mammals, the soft biological tissue, tissue constituting the back of the roof of the mouth. The soft palate is part of the palate of the mouth; the other part is ...

, 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 (spiration or ventilation) is the rhythmical process of moving air into ( inhalation) and out of ( exhalation) the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxy ...

with its underside functioning as part of the

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

. There are

taste bud Taste buds are clusters of taste receptor cells, which are also known as gustatory cells. The taste receptors are located around the small structures known as papillae found on the upper surface of the tongue, soft palate, upper esophagus, ...

s on the epiglottis.

Swallowing

During swallowing, 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

and the

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. The consequence of this is that during swallowing the bent epiglottis blocks off the

, preventing food from going into it; food instead travels down the

, 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

The inflammation of the epiglottis is known as epiglottitis. Epiglottitis is mainly caused by ''

''. 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 pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

s, inhaled aerosolised epinephrine to act as a bronchodilator, and may require

tracheal intubation Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic catheter, tube into the vertebrate trachea, trachea (windpipe) to maintain an open airway or to serve as a conduit through which to administer c ...

or a tracheostomy if breathing is difficult. The incidence of epiglottitis has decreased significantly in countries where

vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulating ...

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 the obstruction of airways, 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 incl ...

; and in the long term, atelectasis and bronchiectasis. One reason aspiration can occur is because of failure of the epiglottis to close completely. 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. 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.

Other animals

The epiglottis is present in

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

, including land mammals and

cetaceans Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...

, 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 Aristotle (; 384–322 BC) was an Ancient Greek philosophy, Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, a ...

, although the epiglottis' function was first defined by

Vesalius Andries van Wezel (31 December 1514 – 15 October 1564), Latinization of names, latinized as Andreas Vesalius (), was an anatomist and physician who wrote ''De humani corporis fabrica, De Humani Corporis Fabrica Libri Septem'' (''On the fabric ...

in 1543. The word has Greek roots. The epiglottis gets its name from being above () the

().

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

References

External links

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