Epiglottis

Structure

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 (). 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 larynx, and is attached to the hyoid bone. From there, it projects upwards and backwards behind the tongue. 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 body of the epiglottis consists of elastic cartilage.

Development

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. 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 with its underside functioning as part of the pharynx.

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 hyoid bone and the larynx move upward and forward, 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 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.

Clinical significance

Inflammation

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.

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 the obstruction of airways, inflammation of lung tissue, and aspiration pneumonia; 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, including land mammals and cetaceans, 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 () the glottis ().

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

References

1. (2016). "Gray's anatomy : the anatomical basis of clinical practice".
2. (November 2008). "Anatomy and Physiology of Feeding and Swallowing – Normal and Abnormal". Physical Medicine and Rehabilitation Clinics of North America.
3. (2018). "Nose, Sinus, Pharynx, and Larynx". Elsevier.
4. Schoenwolf, Gary C.. (2009). "Larsen's human embryology". Churchill Livingstone/Elsevier.
5. (2007). "High-rising epiglottis in children: should it cause concern?". J Am Board Fam Med.
6. (November 1998). "Mucosa and taste buds of the human epiglottis". Journal of Anatomy.
7. (2010). "Davidson's principles and practice of medicine". Churchill Livingstone/Elsevier.
8. (April 2013). "Acute epiglottitis in the era of post-Haemophilus influenzae type B (HIB) vaccine". J Anesth.
9. (April 2014). "Low incidence of children with acute epiglottis after introduction of vaccination". Dan Med J.
10. (1 July 2006). "Cough: what's in a name?". European Respiratory Journal.
11. (13 December 2005). "Silent Aspiration: What Do We Know?". Dysphagia.
12. (2008). "The Trauma Manual: Trauma and Acute Care Surgery". Lippincott Williams & Wilkins.
13. (2018). "The epiglottis and obstructive sleep apnoea syndrome". The Journal of Laryngology & Otology.
14. Leroi, Armand Marie. (2014-08-28). "The Lagoon: How Aristotle Invented Science". Bloomsbury Publishing.
15. (2009-02-26). "Encyclopedia of Marine Mammals". Academic Press.
16. (2008). "Clinical Anatomy and Physiology for Veterinary Technicians". Mosby Elsevier.
17. (2012-01-23). "The Laboratory Rabbit, Guinea Pig, Hamster, and Other Rodents". Academic Press.
18. (2011). "Rabbit Respiratory System: Clinical Anatomy, Physiology and Disease". Veterinary Clinics of North America: Exotic Animal Practice.
19. (2017-08-29). "Comparative Anatomy and Histology: A Mouse, Rat, and Human Atlas". Academic Press.
20. (2012-01-09). "Issues in Anatomy, Physiology, Metabolism, Morphology, and Human Biology: 2011 Edition". ScholarlyEditions.
21. (March 2010). "The historical Latin and etymology of selected anatomical terms of the larynx". Clin Anat.
22. "epiglottis {{!}} Origin and meaning of epiglottis by Online Etymology Dictionary".