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==Overview==
The '''esophagus''' ([[American English]]) or '''oesophagus''' ([[British English]]), commonly known as the '''foodpipe''' or '''gullet''', is an [[Organ (anatomy)|organ]] in [[vertebrate]]s which consists of a [[:wiktionary:fibromuscular|fibromuscular]] tube through which [[food]] passes, aided by [[Peristalsis|peristaltic contractions]], from the [[Human pharynx|pharynx]] to the [[stomach]]. In humans, the esophagus is usually 18–25&nbsp;centimeters (cm) long. During swallowing the [[epiglottis]] tilts backwards to prevent food from going down the [[larynx]]. The esophagus travels behind the [[trachea]] and [[human heart|heart]], passes through the [[Thoracic diaphragm|diaphragm]] and empties into the cardia of the stomach. The word ''esophagus'' derives from the [[Greek language|Greek]] word ''oisophagos'', which means "to carry to eat."<ref name=Harper2014/>

The wall of the esophagus from the [[Lumen (anatomy)|lumen]] outwards consists of [[mucosa]], sub-mucosa (connective tissue), layers of muscle fibers between layers of [[fibrous tissue]], and an outer layer of connective tissue. The mucosa is a [[stratified squamous epithelium]] (multiple layers of cells topped by a layer of flat cells) which contrasts to the [[simple columnar epithelia|single layer of columnar cells]] of the stomach. The transition between these two type of epithelium is visible as a zig-zag line.  Most of the muscle is [[smooth muscle]] although [[striated muscle]] predominates in its upper two thirds. It has two muscular rings or [[sphincter]]s in its wall, one at the top and one at the bottom. The lower sphincter helps to prevent reflux of acidic stomach content. The esophagus has a rich blood supply and vascular drainage. Its smooth muscle is innervated by involuntary nerves ([[sympathetic nerve]]s via the [[sympathetic trunk]] and [[parasympathetic nerve]]s via the [[vagus nerve]]) and in addition voluntary nerves ([[lower motor neurons]]) are carried in the vagus nerve to innervate its striated muscle.

The esophagus may be affected by [[GERD|gastric reflux]], [[esophageal cancer|cancer]], prominent dilated blood vessels called [[oesophageal varices|varices]] that can bleed heavily, [[Mallory-Weiss Syndrome|tears]], constrictions, and disorders of motility. Clinical investigations include X-rays using [[barium]], endoscopy, and [[CT scan]]s.

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==Structure==
The esophagus is one of the upper parts of the [[digestive system]]. At the mouth opening, it is continuous with the back of the oral cavity, passing downwards through the rear part of the [[mediastinum]], through the [[thoracic diaphragm|diaphragm]], and into the [[stomach]]. In humans, the esophagus generally starts around the level of the sixth [[Cervical vertebrae|cervical vertebra]] (C6) behind the [[cricoid cartilage]], enters the diaphragm at about the level of the [[Thoracic vertebrae#Tenth thoracic vertebra|tenth thoracic vertebra]] (T10), and ends at the [[cardia]] of the stomach, at the level of the [[Thoracic vertebrae#Eleventh thoracic vertebra|eleventh thoracic vertebra]] (T11).<ref name=GRAYS2005>{{cite book|last=Drake|first=Richard L.|title=Gray's anatomy for students|year=2005|publisher=Elsevier/Churchill Livingstone|location=Philadelphia|isbn=978-0-8089-2306-0|author2=Vogl, Wayne; Tibbitts, Adam W.M. Mitchell ; illustrations by Richard; Richardson, Paul|pages=192–194}}</ref> The esophagus is usually about 25&nbsp;cm (10&nbsp;in) in length.<ref name=DAVIDSONS2010>{{cite book|editor-first=Nicki R. |editor-last=Colledge |editor-first2=Brian R. |editor-last2=Walker |editor-first3=Stuart H. |editor-last3=Ralston |others=illust. Robert Britton|title=Davidson's Principles and Practice of Medicine |year=2010|publisher=Churchill Livingstone/Elsevier|location=Edinburgh|isbn=978-0-7020-3084-0|edition=21st|page=838}}</ref>

Many [[blood vessel]]s serve the esophagus, with blood supply varying along its course. The cervical parts of the esophagus and the upper esophageal sphincter receive blood from [[inferior thyroid artery]], the parts of the esophagus in the thorax from the [[bronchial artery|bronchial arteries]] and branches directly from the [[thoracic aorta]], and the lower parts of the esophagus and the lower esophageal sphincter (LES) receive blood from the [[left gastric artery]] and the left [[inferior phrenic artery]].<ref name=KUO2006/><ref name=PATTI1997>{{cite journal|last=Patti|first=MG|author2=Gantert, W |author3=Way, LW |title=Surgery of the esophagus. Anatomy and physiology.|journal=The Surgical clinics of North America|date=Oct 1997|volume=77|issue=5|pages=959–70|pmid=9347826|doi=10.1016/s0039-6109(05)70600-9}}</ref> The venous drainage also differs along the course of the esophagus. The upper and lower parts of the esophagus drain into the [[azygos vein|azygos]] and [[hemiazygos vein]]s, and blood from the middle part drains into the [[left gastric vein]]. All these veins drain into the [[superior vena cava]], with the exception of the left gastric vein, which is a branch of the [[portal vein]].<ref name=KUO2006/> Lymphatically, the upper third of the esophagus drains into the [[deep cervical lymph node]]s, the middle into the superior and posterior mediastinal lymph nodes, and the lower esophagus into the [[gastric lymph nodes|gastric]] and [[celiac lymph nodes]].<ref name=KUO2006/>

The esophagus is innervated by the vagus nerve and the cervical and thoracic [[sympathetic trunk]].<ref name=KUO2006/> The vagus nerve has a [[parasympathetic nerve|parasympathetic]] function, supplying the muscles of the esophagus and stimulating glandular contraction. Two sets of nerve fibres travel in the vagus nerve to supply the muscles. The upper striated muscle, and upper esophageal sphincter, are supplied by neurons with bodies in the [[nucleus ambiguus]], whereas fibres that supply the smooth muscle and lower esophageal sphincter have bodies situated in the [[dorsal motor nucleus]].<ref name=KUO2006/> The vagus nerve plays the primary role in initiating peristalsis.<ref>{{cite journal|last=Patterson|first=William G.|title=Esophageal peristalsis|journal=GI Motility online|date=2006|doi=10.1038/gimo13|url=http://www.nature.com/gimo/contents/pt1/full/gimo13.html|accessdate=24 May 2014|doi_brokendate=2015-01-12}}</ref> The sympathetic trunk has a [[sympathetic nerve|sympathetic]] function. It may enhance the function of the vagus nerve, increasing peristalsis and glandular activity, and causing sphincter contraction. In addition, sympathetic activation may relax the muscle wall and cause blood vessel constriction.<ref name=KUO2006/> Sensation along the esophagus is supplied by both nerves, with gross sensation being passed in the vagus nerve and pain passed up the sympathetic trunk.<ref name=GRAYS2005 />

;Position
{{multiple image
| align     = right

| image1    = Relations of the aorta, trachea, esophagus and other heart structures.png
| width1    = 200
| alt1      = Diagram showing the esophagus passing behind the human trachea and heart.
| caption1  = The esophagus (yellow) passes behind the [[human trachea|trachea]] and the [[human heart|heart]].

| image2    = Gray1032.png 
| width2    = 200
| alt2      = Diagram of thorax showing the esophagus and surrounding structures.
| caption2  = The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.
}}
The upper esophagus lies at the back of the mediastinum behind the [[trachea]], and in front of the [[erector spinae muscle]]s and the [[vertebral column]]. The lower esophagus lies behind the [[heart]] and curves in front of [[thoracic aorta]]. From the [[Carina of trachea|bifurcation of the trachea]] downwards, the esophagus passes behind the right [[pulmonary artery]], [[left main bronchus]], and [[left atrium]]. At this point it passes through the diaphragm.<ref name=GRAYS2005 />

The [[thoracic duct]], which drains the majority of the body's [[lymph]], passes behind the esophagus, curving from lying behind the esophagus on the right in the lower part of the esophagus, to lying behind the esophagus on the left in the upper esophagus. The esophagus also lies in front of parts of the [[hemiazygos vein]]s and the [[intercostal vein]]s on the right side. The [[vagus nerve]] divides and covers the esophagus in a [[plexus]].<ref name=GRAYS2005 />

;Constrictions
The esophagus has four points of constriction. When corrosive substances are ingested, or a solid object is swallowed, it is most likely to lodge and damage these four points. These constrictions are because of particular structures that compress on the esophagus. These constrictions are:<ref name=GRAYS2005 />
* At the start of the esophagus, where the [[pharynx]] joins the esophagus, behind the [[cricoid cartilage]]
* Where it is crossed on the front by the [[aortic arch]] and the left main [[bronchus]]
* Where it passes through the [[Thoracic diaphragm|diaphragm]]

=== Sphincters ===
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The esophagus is surrounded at the top and bottom by two muscular rings, known respectively as the ''upper esophageal sphincter'' and the ''lower esophageal sphincter''.<ref name=GRAYS2005 /> These [[sphincter]]s act to close the esophagus when food is not being swallowed. The esophageal sphincters are functional, but not anatomical sphincters, meaning that they are sections of the esophageal wall that act as a sphincter, but do not have distinct thickenings like other sphincters.<ref name=GUYTONHALL2005 />

The ''upper esophageal sphincter'' surrounds the upper part of the esophagus. It consists of [[skeletal muscle]], but is not under [[conscious]] control. Opening of the upper esophageal sphincter is triggered by the swallow reflex. The primary muscle of the upper esophageal sphincter is the cricopharyngeus portion of the [[inferior pharyngeal constrictor]].<ref>{{Cite journal|author=Mu L, Wang J, Su H, Sanders I |title=Adult human upper esophageal sphincter contains specialized muscle fibers expressing unusual myosin heavy chain isoforms |journal=J. Histochem. Cytochem. |volume=55 |issue=3 |pages=199–207 |date=March 2007 |pmid=17074861 |doi=10.1369/jhc.6A7084.2006|last2=Wang |last3=Su |last4=Sanders |doi_brokendate=2015-01-12 }}</ref>

The ''lower esophageal sphincter'' surrounds the lower part of the esophagus. This sphincter surrounds the junction between the esophagus and the stomach.<ref name=GUYTONHALL2005 />

===Gastro-esophageal junction===
The gastro-esophageal junction (also known at the esophagogastic junction) is the junction between the esophagus and the stomach, and it is situated at the lower end of the esophagus.<ref>{{Cite encyclopedia|title=Stedman's Concise Medical and Allied Health Dictionary | author= John H. Dirckx (editor) |year=1997 |isbn=0-683-23125-1|publisher=[[Williams and Wilkins]] |edition=3rd  |page=463}}</ref> The pink color of the esophageal mucosa contrasts to the a deeper red of the gastric mucosa,<ref name=KUO2006/><ref name=GD2002>{{cite book|editor= Anthony DiMarino, Jr., Stanley B. Benjamin ; section editors, Firas H. Al-Kawas |title=Gastrointestinal disease : an endoscopic approach|year=2002|publisher=Slack|location=Thorofare, NJ|isbn=978-1-55642-511-0|page=166|edition=2nd}}</ref> and the mucosal transition can be seen as an irregular zig-zag line, which is often called the z-line.<ref>{{cite book|last=Levine|first=editors, Richard M. Gore, Marc S.|title=High-yield imaging.|date=2010|publisher=Saunders/Elsevier|location=Philadelphia, Pa.|isbn=1455711446|page=151|edition=1st}}</ref> Similarly, by direct vision of fresh specimens, grey-pink of the esophageal mucosa contrasts with the darker gastric mucosa,<ref>{{Cite book |first=Henry |last=Gray |author-link=Henry Gray |editor1-last=Johnston |editor1-first=T.B |editor2-last=Whillis |editor2-first=J |title=[[Gray's Anatomy: Descriptive and Applied]] |edition=28th |year=1942 |publisher=[[Longmans, Green and Co.]] |page=1318}}</ref> but in embalmed cadavers a color contrast may not be apparent.<ref name=Moore-Agur>{{cite book|title=Essential Clinical Anatomy |edition=2nd |first1=Keith L |last1=Moore |first2=Anne M.R |last2=Agur |publisher=[[Lippincott Williams & Wilkins]] | year=2002 |isbn=0-7817-2830-4 |page=145}}</ref>  Histological examination reveals abrupt transition between the nonkeratinized [[stratified squamous epithelium]] of the esophagus and the [[simple columnar epithelium]] of the [[stomach]].<ref name=Moore-Agur/> Normally, the cardia of the [[stomach]] is immediately distal to the z-line<ref>{{cite book|last=Barrett|first=Kim E.|title=Gastrointestinal physiology|year=2014|publisher=Mc Graw Hill.|location=New York|isbn=978-0-07-177401-7|pages=Chapter 7: "Esophageal Motility"|edition=2nd}}</ref> and the z-line coincides with the upper limit of the gastric folds of the cardia; however, when the anatomy of the mucosa is distorted in [[Barrets esophagus]] the true gastro-eshophageal junction can be identified by the upper limit of the gastric folds rather than the mucosal transition.<ref>{{cite book|title=Specialist Training in Gastroenterology and Liver Disease |editor1-first=Richard G |editor1-last=Long |editor2-first=Brian B |editor2-last=Scott |isbn=0-7234-3252-X | publisher=Elsevier Mosby |year=2005 |pages=25–26}}</ref> The functional location of LES is generally situated about 3&nbsp;cm distal to the z-line.<ref name=KUO2006>{{cite journal |last1=Kuo|first1=Braden |last2=Urma |first2=Daniela|url=http://www.nature.com/gimo/contents/pt1/full/gimo6.html|title=Esophagus - anatomy and development|journal=GI Motility online|date=2006|doi=10.1038/gimo6|doi_brokendate=2015-01-12 }}</ref>

===Histology===
{{Main|Gastrointestinal wall}}
{{multiple image
| align     = right

| image1    = Tinción hematoxilina-eosina.jpg
| width1    = 150
| alt1      = Histological section of the esophageal wall.
| caption1  = [[H&E]] stain of a [[biopsy]] of the normal esophageal wall, showing the stratified [[squamous cell]] [[epithelium]] of the esophageal wall.

| image2    = Gastro-esophageal jxn.JPG 
| width2    = 150
| alt2      = Histological section showing the gastroesophageal junction, with a black arrow pointing to the junction.
| caption2  = [[Histology|Histological]] section of the gastro-esophageal junction, with a black arrow indicating the junction.
}}
The human esophagus has a [[mucosa]] consisting of a tough [[stratified squamous epithelium]] without [[keratin]], a smooth [[lamina propria]], and a [[muscularis mucosa]].<ref name=KUO2006 /> The epithelium of the esophagus has a relatively rapid turnover, and serves a protective function against the abrasive effects of food. In many animals the epithelium contains a layer of keratin, representing a coarser diet.<ref name="ross">{{cite book | title=Histology: A Text and Atlas | publisher=Lippincott Williams & Wilkins | author=Ross M, Pawlina W | year=2011 | isbn=978-0-7817-7200-6 | pages=571–573 | edition=6th}}</ref>  Protection is conferred by the secretion of [[mucus]] from glands.<ref>{{cite book|editor-first=Barbara |editor-last=Young |title=Wheater's functional histology: a text and colour atlas|date=2006|publisher=Churchill Livingstone/Elsevier|isbn=978-0-443-068-508|page=86|edition=5th}}</ref> There are two types of glands, with mucus-secreting esophageal glands being found in the [[submucosa]], and esophageal cardiac glands, similar to [[cardiac glands]] of the stomach, located in the lamina propria and most frequent in the terminal part of the organ.<ref name="ross"/><ref>{{cite book|last=Takubo|first=Kaiyo|title=Pathology of the esophagus an atlas and textbook|date=2007|publisher=Springer Verlag|location=Tokyo|isbn=9784431686163|page=28|edition=2nd}}</ref> The submucosa also contains the [[submucosal plexus]], a network of [[neuron|nerve cells]] part of the [[enteric nervous system]].<ref name=ross />

The [[muscularis propria]] of the esophagus has two types of muscle. The upper third of the esophagus contains [[striated muscle]] and the lower third contain [[smooth muscle]], with the middle third containing a mixture of both.<ref name=KUO2006 /> Muscle is arranged in two layers: one in which the muscle fibres run longitudinal to the esophagus, and the other in which the fibres encircle the esophagus. These are separated by the [[myenteric plexus]], a tangled interpolation of nerve fibres involved in the secretion of mucus and peristalsis of the smooth muscle of the esophagus. The esophagus also has an [[adventitia]], but not a [[serosa]]. This makes it distinct from many other structures in the gastrointestinal tract.<ref name=KUO2006 />

==Development==
The esophagus develops from the embryonic gut tube, an [[endoderm]]al structure. Early in development, the human embryo has three layers and abuts an embryonic [[yolk sac]]. During the second week of embryological development, as the embryo grows, it begins to surround and envelop portions of this sac. The enveloped portions form the basis for the adult gastrointestinal tract. Sections of this gut begin to differentiate into the organs of the gastrointestinal tract, such as the esophagus, [[stomach]], and [[intestine]]s.<ref name=LARSEN2009 />

The sac is surrounded by a network of arteries called the [[vitelline veins|vitelline plexus]]. Over time, these arteries consolitate into three main arteries that supply the developing gastrointestinal tract: the [[celiac artery]], [[superior mesenteric artery]], and [[inferior mesenteric artery]]. The areas supplied by these arteries are used to define the midgut, hindgut and [[foregut]].<ref name=LARSEN2009 />

The esophagus develops as part of the foregut tube.<ref name=LARSEN2009>{{cite book|author=Gary C. Schoenwolf |title=Larsen's human embryology|year=2009|publisher=Churchill Livingstone/Elsevier|location=Philadelphia|isbn=978-0-443-06811-9|chapter=Development of the Gastrointestinal Tract|edition=4th}}</ref> The innervation of the esophagus develops from the [[branchial arch]]es.<ref name=GRAYS2005 />

==Function==

===Swallowing===
In humans and other animals, food is [[ingestion|ingested]] through the [[mouth]]. During [[swallowing]], food passes from the mouth through the [[pharynx]] into the esophagus. The esophagus is thus one of the first components of the [[human digestive system]] and the [[human gastrointestinal tract]]. After food passes through the esophagus, it enters the [[stomach]].<ref name=GUYTONHALL2005>{{cite book|last=Hall|first=Arthur C. Guyton, John E.|title=Textbook of medical physiology|year=2005|publisher=W.B. Saunders|location=Philadelphia|isbn=978-0-7216-0240-0|pages=782–784|edition=11th}}</ref>

When food is being swallowed, the [[epiglottis]] moves backward to cover the [[larynx]], preventing food from entering the [[trachea]]. At the same time, the upper esophageal sphincter relaxes, allowing a [[Bolus (digestion)|bolus]] of food to enter. Rhythmic contraction of the esophageal muscle called [[peristalsis]] pushes the food down the esophagus. These rhythmic contractions occur both as a reflex response to food that is in the mouth, and also as a response to the sensation of food within the esophagus itself. Along with the peristalsis, the lower esophageal sphincter relaxes.<ref name=GUYTONHALL2005 />

===Reducing gastric reflux===
The stomach generates strong acids, including [[hydrochloric acid]] (HCl), and [[enzyme]]s to aid in food [[digestion]]. This digestive mixture is called [[gastric juice]]. Constriction of the upper and lower esophageal sphincters help to prevent reflux of gastric contents and juices into the esophagus, protecting the esophageal mucosa. In addition, the acute [[angle of His]] and the lower [[crura of the diaphragm]] helps this sphincteric action.<ref name=GUYTONHALL2005 /><ref>{{cite web|url=http://www.ncbi.nlm.nih.gov/books/NBK54272/ |title=Neuromuscular Anatomy of Esophagus and Lower Esophageal Sphincter - Motor Function of the Pharynx, Esophagus, and its Sphincters - NCBI Bookshelf |publisher=Ncbi.nlm.nih.gov |date=2013-03-25 |accessdate=2013-04-24}}</ref>

==Clinical significance==
The main conditions affecting the esophagus are described here. For a more complete list, see [[esophageal disease]].

===Inflammation===
Inflammation of the esophagus is known as [[esophagitis]]. [[GERD|Reflux of gastric acids]] from the stomach, infection, substances ingested (for example, corrosives), some medications (such as [[bisphosphonate]]s), food allergies, and  can all lead to esophagitis. {{As of|2014}} the cause of some forms of esophagitis, such as [[eosinophilic esophagitis]], is not known. Esophagitis can cause [[Odynophagia|painful swallowing]] and is usually treated by managing the cause of the esophagitis - such as managing reflux or treating infection.<ref name=DAVIDSONS2010>{{cite book|editor= Nicki R. Colledge, Brian R. Walker, Stuart H. Ralston |others= illustrated by Robert Britton|title=Davidson's Principles and Practice of Medicine |year=2010|publisher=Churchill Livingstone/Elsevier|location=Edinburgh|isbn=978-0-7020-3084-0|edition=21st|pages=860–870}}</ref>

===Cancer===
[[Esophageal cancer|Cancer of the esophagus]] may occur in two forms. If the cancer occurs in the squamous cells lining the esophagus, it is called a [[carcinoma]]. Such a cancer is more common in [[China]] and [[Iran]]. If the cancer occurs in the glands or columnar tissue of the esophagus, then the cancer is an [[adenocarcinoma]]. This is most common in Western countries in those with Barrett's esophagus, and occurs in the cuboidal cells.<ref name=DAVIDSONS2010 />

In its early stages, esophageal cancer may not have any symptoms at all. When severe, esophageal cancer may eventually cause obstruction of the esophagus, making swallowing of any solid foods very difficult and causing weight loss. The progress of the cancer is [[TNM staging|staged using a system]] that measures how far into the esophageal wall the cancer has invaded, how many [[lymph node]]s possess the cancer, and whether there are any [[metastases]] in different parts of the body. Esophageal cancer is often managed with radiotherapy, chemotherapy, and may also be managed by [[esophagectomy|partial surgical removal of the esophagus]]. Inserting a stent into the esophagus, or inserting a [[nasogastric tube]], may also be used to ensure that a person is able to digest enough food and water. {{As of|2014}}, the prognosis for esophageal cancer is still poor, so [[palliative therapy]] may also be a focus of treatment.<ref name=DAVIDSONS2010/>

===Barrett's esophagus===
Prolonged esophagitis, particularly from gastric reflux, is one factor thought to play a role in the development of [[Barrett's esophagus]]. In this condition, there is [[metaplasia]] of the lining of the lower esophagus, which changes from [[stratified squamous epithelia]] to [[simple columnar epithelia]].  Barrett's esophagus is thought to be one of the main contributors to the development of esophageal cancer.<ref name=DAVIDSONS2010 />

===Varices===
[[Esophageal varices]] refer to engorged blood vessels present within the esophageal walls. These blood vessels are engorged more than normal, and in the worst cases may partially obstruct the esophagus. These blood vessels develop as part of a collateral circulation that occurs to drain blood from the [[abdomen]] as a result of [[portal hypertension]], usually as a result of [[liver disease]]s such as [[cirrhosis]].<ref name=DAVIDSONS2010>{{cite book|first=the editors Nicki R. Colledge, Brian R. Walker, Stuart H. Ralston ; illustrated by Robert Britton|title=Davidson's Principles and Practice of Medicine |year=2010|publisher=Churchill Livingstone/Elsevier|location=Edinburgh|isbn=978-0-7020-3084-0|edition=21st|pages=941–942}}</ref> This collateral circulation occurs because the lower part of the esophagus drains into the left gastric vein, which is a branch of the portal vein. Because of the extensive venous plexus that exists between this vein and other veins, if portal hypertension occurs, the direction of blood drainage in this vein may reverse, with blood draining from the portal venous system, through the plexus. Veins in the plexus may engorge and lead to varices.<ref name=KUO2006/><ref name=PATTI1997/>

Esophageal varices often do not have symptoms until they rupture. A ruptured varix is considered a medical emergency, because varices can bleed a lot. A bleeding varix may cause a person [[haematemesis|to throw up blood]], or may cause symptoms of [[hypovolemic shock]]. To deal with a ruptured varix, a band may be placed around the bleeding bood vessel, or a small amount of a clotting agent may be injected near the bleed. A surgeon may also try to use a small inflatable balloon to apply pressure to stop the wound. A person with a bleeding varice may also receive [[IV fluids]] in order to prevent [[hypovolemic shock]] from excess blood loss.<ref name=DAVIDSONS2010 />

===Motility disorders===
Several disorders affect the motility of food as it travels down the esophagus. This can cause difficult swallowing, called [[dysphagia]]. [[Achalasia]] refers to a failure of the lower esophageal sphincter to relax properly, and generally develops later in life. This leads to progressive enlargement of the esophagus, and possibly eventual [[megaesophagus]]. A [[nutcracker esophagus]] refers to swallowing that can be extremely painful, and [[diffuse esophageal spasm]] refers to spasm of the esophagus that can be one cause of chest pain. Sclerosis of the esophagus, such as with [[systemic sclerosis]] or in [[CREST syndrome]] may cause hardening of the walls of the esophagus and interfere with peristalsis.<ref name=DAVIDSONS2010 />

===Malformations===
Various structures may also constrict the esophagus. These esophageal strictures are usually benign and typically develop after a person has had reflux for many years. Other malformations may include [[esophageal web]]s (which can also be congenital) and damage to the esophagus by radiotherapy, corrosive ingestion, or eosinophilic esophagitis. A [[Schatzki ring]] is fibrosis at the gastro-esophageal junction. Strictures may also develop in chronic [[anemia]], and [[Plummer-Vinson]] syndrome.<ref name=DAVIDSONS2010 />

===Congenital malformation===
The esophagus [[esophageal atresia|fails to develop]] or there is an [[fistula|abnormal connection]] [[Tracheoesophageal fistula|between the trachea and esophagus]] in about 1 in 3500 births. Conventional classification divides such connections into five types, based on whether the esophagus is a continuous tube or not, and which end of the esophagus (proximal, distal, both or neither) connects to the trachea. About half the time, these abnormalities occurs with additional abnormalities in other parts of the body, especially affecting the heart.<ref>{{cite journal|last=Shaw-Smith|first=C|title=esophageal atresia, tracheo-esophageal fistula, and the VACTERL association: review of genetics and epidemiology|journal=Journal of Medical Genetics|date=18 November 2005|volume=43|issue=7|pages=545–54|doi=10.1136/jmg.2005.038158|pmid=16299066|pmc=2564549}}</ref>

==Imaging==
An [[X-ray]] of [[Barium swallow|swallowed barium]] may be used to reveal the size and shape of the esophagus, and the presence of any masses. The esophagus may also be [[medical imaging|imaged]] using a flexible camera inserted into the esophagus, in a procedure called an [[endoscopy]]. If an endoscopy is used on the stomach, the camera will also have to pass through the esophagus. During an endoscopy, a [[biopsy]] may be taken. If cancer of the esophagus is being investigated, other methods, including a [[CT scan]], may also be used.<ref name=DAVIDSONS2010 />

==History==
The word ''esophagus'' ([[British English]]: oesophagus) comes from {{lang-el|οἰσοφάγος}} (''oisophagos''), from "to carry" (''oesin'') and "to eat" (''phagos'').<ref name=Harper2014>{{cite web|last=Harper|first=Douglas|title=Esophagus|url=http://www.etymonline.com/index.php?term=esophagus&allowed_in_frame=0|work=Etymology Online|accessdate=19 March 2014}}</ref> The Greek term oesophagus, from which the English term has been derived, has been documented in anatomical literature since at least the time of [[Hippocrates]], who noted that "the oesophagus&nbsp;... receives the greatest amount of what we consume." <ref>{{cite book|first=Hippocrates ;edited|title=Coan prenotions.|year=2010|publisher=Harvard University Press|location=Cambridge, Mass.|isbn=0-674-99640-2|edition=1. publ.|author=Potter, translated by Paul|page=59}}</ref> Its existence in other animals and its relationship with the [[stomach]] was documented by the [[Ancient Rome|Ancient Roman]] ([[philosopher]]) and physician [[Pliny the Elder]],<ref>{{cite book|last=Bostock|first=John; Riley, Henry T.; Pliny the Elder|title=The natural history of Pliny|year=1855|publisher=H. G. Bohn|location=London|page=64|url=https://archive.org/details/naturalhistoryof03plin}}</ref> and the [[peristalsis|peristaltic]] contractions of the esophagus have been documented since at least the time of [[Galen]].<ref>{{cite book|last=Brock|first=Galen ; with an English translation  by Arthur John|title=On the natural faculties|year=1916|publisher=W. Heinemann|location=London|isbn=978-0-674-99078-4|page="Book 3" S8|edition=Repr.|url=http://classics.mit.edu/Galen/natfac.3.three.html}}</ref>

The first attempt at surgery on the esophagus focused in the neck, and was firstly conducted in dogs by [[Theodore Billroth]] in 1871, and then in people by [[Czerny]] in 1877. By 1908, an operation had been performed by [[Voeckler]] to remove the esophagus, and in 1933 the first surgical removal of parts of the lower esophagus, (to control [[esophageal cancer]]), had been conducted.<ref name=NORTON2008>{{cite book|editor-first=Jeffrey A. |editor-last=Norton|title=Surgery : basic science and clinical evidence|year=2008|publisher=Springer|location=New York, NY|isbn=978-0-387-30800-5|edition=2nd|pages=744–746}}</ref>

The [[Nissen fundoplication]], in which the stomach is wrapped around the lower [[esophageal sphincter]] in order to stimulate its function and control [[GERD|reflux]], was first conducted by [[Rudolph Nissen]] in 1955.<ref name=NORTON2008 />

==Other animals==

===Vertebrates===
In [[tetrapod]]s, the pharynx is much shorter, and the esophagus correspondingly longer, than in fish. In the majority of vertebrates, the esophagus is simply a connecting tube, but in some [[bird]]s, which regurgitate components to feed their young, it is extended towards the lower end to form a [[crop (anatomy)|crop]] for storing food before it enters the true stomach.<ref name=VB/><ref name=CA>{{cite book|last=Hume|first=C. Edward Stevens, Ian D.|title=Comparative physiology of the vertebrate digestive system|year=2005|publisher=Cambridge University Press|location=Cambridge|isbn=978-0-521-61714-7|page=15|edition=1st pbk.}}</ref>  In [[ruminant]]s, animals with four stomachs, a groove called the ''sulcus reticuli'' is often found in the esophagus, allowing milk to drain directly into the hind stomach, the [[abomasum]].<ref>{{cite journal|last=Mackie|first=R. I.|title=Mutualistic Fermentative Digestion in the Gastrointestinal Tract: Diversity and Evolution|journal=Integrative and Comparative Biology|date=1 April 2002|volume=42|issue=2|pages=319–326|doi=10.1093/icb/42.2.319|pmid=21708724}}</ref> The esophagus of [[snake]]s is remarkable for the distension it undergoes when swallowing prey.<ref>{{Cite journal | doi = 10.1002/ar.22860|journal=Anat Rec |date=Mar 2014|volume=297|issue=3|pages=586–98|title=A model of the anterior esophagus in snakes, with functional and developmental implications|author=Cundall D, Tuttman C, Close M.|last2=Tuttman |last3=Close }}</ref>

In most fish, the esophagus is extremely short, primarily due to the length of the pharynx (which is associated with the [[gill]]s). However, some fish, including [[lamprey]]s, [[chimaera]]s, and [[lungfish]], have no true stomach, so that the esophagus effectively runs from the pharynx directly to the [[intestine]], and is therefore somewhat longer.<ref name=VB>{{cite book |author=Romer, Alfred Sherwood|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA|pages= 344–345|isbn= 0-03-910284-X}}</ref>

In many vertebrates, the esophagus is lined by [[stratified squamous epithelia]] without glands. In fish, the esophagus is often lined with [[columnar epithelia]],<ref name=CA /> and in [[amphibian]]s, [[shark]]s and [[ray (fish)|rays]], the esophageal epithelium is [[cilia]]ted, helping to wash food along, in addition to the action of muscular peristalsis.<ref name=VB/> In addition, in the [[bat]] ''[[Plecotus auritus]]'', fish and some amphibians, glands secreting [[pepsinogen]] or [[hydrochloric acid]] have been found.<ref name=CA />

The muscle of the esophagus in many mammals is striated initially, but then becomes smooth muscle in the caudal third or so. In the canine and ruminants, however, it is entirely striated to allow regurgitation to feed young (canines) or regurgitation to chew cud (ruminants). It is entirely smooth muscle in amphibians, reptiles and birds.<ref name=CA/>

Contrary to popular belief,<ref>{{cite news|last=Eveleth|first=Rose|title=Could a Whale Accidentally Swallow You? It Is Possible|url=http://www.smithsonianmag.com/smart-news/could-a-whale-accidentally-swallow-you-it-is-possible-26353362/?no-ist|accessdate=12 April 2014|newspaper=Smithsonian|date=20 February 2013}}</ref> a person would not be able to pass through the esophagus of a [[whale]], which generally measure less than 10&nbsp;cm in diameter, although in larger [[baleen whale]]s may be up to ten inches when fully distended.<ref>{{cite book|last=Tinker|first=Spencer Wilkie|title=Whales of the world|year=1988|publisher=E.J. Brill|location=Leiden|isbn=978-0-935848-47-2|page=60|url=https://books.google.com/?id=ASIVAAAAIAAJ&pg=PA60&lpg=PA60&dq=how+long+is+a+whale%27s+esophagus#v=onepage&q=how%20long%20is%20a%20whale%27s%20esophagus&f=false}}</ref>

===Invertebrates===

A structure with the same name is often found in invertebrates, including [[mollusc]]s and [[arthropod]]s, connecting the oral cavity with the stomach.<ref>{{cite journal|last=Hartenstein|first=Volker|title=Development of the insect stomatogastric nervous system|journal=Trends in Neurosciences|date=September 1997|volume=20|issue=9|pages=421–427|doi=10.1016/S0166-2236(97)01066-7|pmid=9292972}}</ref> In the [[cephalopod]]s, the brain often surrounds the esophagus.<ref>{{cite book|last=Kutsch|first=with a coda written by T.H. Bullock ; edited by O. Breidbach, W.|title=The nervous systems of invertebrates : an evolutionary and comparative approach|year=1994|publisher=Birkhäuser|location=Basel|isbn=978-3-7643-5076-5|page=117}}</ref>

The mouth of [[gastropods]] opens into an esophagus, which connects to the stomach. Because of torsion, the esophagus usually passes around the stomach, and opens into its posterior portion, furthest from the mouth. In species that have undergone de-torsion, however, the esophagus may open into the anterior of the stomach, which is therefore reversed from the usual gastropod arrangement.<ref name="Barnes1982">{{cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location= Philadelphia, PA|isbn= 0-03-056747-5}}</ref>

In [[Tarebia granifera]] the brood pouch is above the esophagus.<ref name="Appleton 2009">Appleton C. C., Forbes A. T.& Demetriades N. T. (2009). "The occurrence, bionomics and potential impacts of the invasive freshwater snail ''Tarebia granifera'' (Lamarck, 1822) (Gastropoda: Thiaridae) in South Africa". ''Zoologische Mededelingen'' '''83'''. http://www.zoologischemededelingen.nl/83/nr03/a04</ref>

There is available an extensive rostrum on the anterior part of the esophagus in all carnivorous gastropods.<ref name="Gerlach 1998">{{Cite journal|doi=10.1093/mollus/64.2.249|title=A first record of a terrestrial mollusc without a radula|year=1998|last1=Gerlach|first1=J.|last2=Van Bruggen|first2=A.C.|journal=Journal of Molluscan Studies|volume=64|issue=2|pages=249}}.</ref>

==See also==
{{Anatomy-terms}}

==References==
{{Reflist|2}}

{{Commons}}
{{Wiktionary|esophagus}}

{{Digestive tract}}
{{Human systems and organs}}

{{Authority control}}

[[Category:Digestive system]]
[[Category:Thorax (human anatomy)]]
[[Category:Organs (anatomy)]]
[[Category:Human head and neck]]
[[Category:Abdomen]]

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