The wall of the esophagus from thelumen outwards consists ofmucosa,submucosa (connective tissue),layers of muscle fibers between layers offibrous tissue, and an outer layer of connective tissue. The mucosa is astratified squamous epithelium of around three layers of squamous cells, which contrasts to thesingle layer of columnar cells of the stomach. The transition between these two types of epithelium is visible as a zig-zag line. Most of the muscle issmooth muscle althoughstriated muscle predominates in its upper third. It has two muscular rings orsphincters 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 venous drainage. Its smooth muscle is innervated by involuntary nerves (sympathetic nerves via thesympathetic trunk andparasympathetic nerves via thevagus nerve) and in addition voluntary nerves (lower motor neurons) which are carried in the vagus nerve to innervate its striated muscle.
The esophagus may be affected bygastric reflux,cancer, prominent dilated blood vessels calledvarices that can bleed heavily,tears, constrictions, and disorders of motility. Diseases may cause difficulty swallowing (dysphagia), painful swallowing (odynophagia),chest pain, or cause no symptoms at all. Clinical investigations includeX-rays when swallowingbarium sulfate,endoscopy, andCT scans. Surgically, the esophagus is difficult to access in part due to its position between critical organs and directly between the sternum and spinal column.[3]
Manyblood vessels serve the esophagus, with blood supply varying along its course. The upper parts of the esophagus and the upper esophageal sphincter receive blood from theinferior thyroid artery, the parts of the esophagus in the thorax from thebronchial arteries and branches directly from thethoracic aorta, and the lower parts of the esophagus and the lower esophageal sphincter receive blood from theleft gastric artery and the leftinferior phrenic artery.[7][8] The venous drainage also differs along the course of the esophagus. The upper and middle parts of the esophagus drain into theazygos andhemiazygos veins, and blood from the lower part drains into theleft gastric vein. All these veins drain into thesuperior vena cava, with the exception of the left gastric vein, which is a branch of theportal vein.[7] Lymphatically, the upper third of the esophagus drains into thedeep cervical lymph nodes, the middle into the superior and posterior mediastinal lymph nodes, and the lower esophagus into thegastric andceliac lymph nodes. This is similar to the lymphatic drainage of the abdominal structures that arise from theforegut, which all drain into the celiac nodes.[7]
Position
The esophagus (yellow) passes behind thetrachea and theheart.
The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.
Thethoracic duct, which drains the majority of the body'slymph, 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 thehemiazygos veins and theintercostal veins on the right side. Thevagus nerve divides and covers the esophagus in aplexus.[5]
Constrictions
The esophagus is constricted in three places.[inconsistent]
The esophagus has four points of constriction. When a corrosive substance, or a solid object is swallowed, it is most likely to lodge and damage one of these four points. These constrictions arise from particular structures that compress the esophagus. These constrictions are:[9]
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.[5] Thesesphincters act to close the esophagus when food is not being swallowed. The upper esophageal sphincter is an anatomical sphincter, which is formed by the lower portion of the inferior pharyngeal constrictor, also known as the cricopharyngeal sphincter due to its relation withcricoid cartilage of thelarynx anteriorly. However, the lower esophageal sphincter is not an anatomical but rather a functional sphincter, meaning that it acts as a sphincter but does not have a distinct thickening like other sphincters.
The lower esophageal sphincter, or gastroesophageal sphincter, surrounds the lower part of the esophagus at the junction between the esophagus and the stomach.[11] It is also called the cardiac sphincter or cardioesophageal sphincter, named from the adjacent part of the stomach, thecardia. Dysfunction of the gastroesophageal sphincter causes gastroesophagealreflux, which causesheartburn, and, if it happens often enough, can lead togastroesophageal reflux disease, with damage of the esophageal mucosa.[12]
The esophagus is innervated by the vagus nerve and the cervical and thoracicsympathetic trunk.[7] The vagus nerve has aparasympathetic function, supplying the muscles of the esophagus and stimulating glandular contraction. Two sets of nerve fibers travel in the vagus nerve to supply the muscles. The upper striated muscle, and upper esophageal sphincter, are supplied by neurons with bodies in thenucleus ambiguus, whereas fibers that supply the smooth muscle and lower esophageal sphincter have bodies situated in thedorsal motor nucleus.[7] The vagus nerve plays the primary role in initiatingperistalsis.[13] The sympathetic trunk has asympathetic 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.[7] 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.[5]
The gastroesophageal junction (also known as the esophagogastric junction) is the junction between the esophagus and the stomach, at the lower end of the esophagus.[14] The pink color of the esophageal mucosa contrasts to the deeper red of the gastric mucosa,[7][15] and the mucosal transition can be seen as an irregular zig-zag line, which is often called the z-line.[16] Histological examination reveals abrupt transition between thestratified squamous epithelium of the esophagus and thesimple columnar epithelium of thestomach.[17] Normally, thecardia of the stomach is immediately distal to the z-line[18] 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 inBarrett's esophagus the true gastroesophageal junction can be identified by the upper limit of the gastric folds rather than the mucosal transition.[19] The functional location of the lower oesophageal sphincter is generally situated about 3 cm (1+1⁄4 in) below the z-line.[7]
The human esophagus has amucous membrane consisting of a toughstratified squamous epithelium withoutkeratin, a smoothlamina propria, and amuscularis mucosae.[7] 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.[20] There are two types of glands, with mucus-secretingesophageal glands being found in thesubmucosa and esophageal cardiac glands, similar tocardiac glands of the stomach, located in the lamina propria and most frequent in the terminal part of the organ.[20][21] Themucus from the glands gives a good protection to the lining.[22] The submucosa also contains thesubmucosal plexus, a network ofnerve cells that is part of theenteric nervous system.[20]
Themuscular layer of the esophagus has two types of muscle. The upper third of the esophagus containsstriated muscle, the lower third containssmooth muscle, and the middle third contains a mixture of both.[7] Muscle is arranged in two layers: one in which the muscle fibers run longitudinal to the esophagus, and the other in which the fibers encircle the esophagus. These are separated by themyenteric plexus, a tangled network of nerve fibers involved in the secretion of mucus and in peristalsis of the smooth muscle of the esophagus. The outermost layer of the esophagus is theadventitia in most of its length, with the abdominal part being covered inserosa. This makes it distinct from many other structures in the gastrointestinal tract that only have a serosa.[7]
In earlyembryogenesis, the esophagus develops from theendodermalprimitive gut tube. The ventral part of the embryo abuts theyolk sac. It is very small in the beginning, but it lengthens due to descent of lungs and heart.[23] During the second week of embryological development, as the embryo grows, it begins to surround parts of the sac. The enveloped portions form the basis for the adult gastrointestinal tract.[24] The sac is surrounded by a network ofvitelline arteries. Over time, these arteries consolidate into the three main arteries that supply the developing gastrointestinal tract: theceliac artery,superior mesenteric artery, andinferior mesenteric artery. The areas supplied by these arteries are used to define themidgut,hindgut andforegut.[24]
The muscle of upper one-third is striated, middle one-third, mixed, and lower one-third smooth.[23]
The surrounded sac becomes the primitive gut. Sections of this gut begin to differentiate into the organs of the gastrointestinal tract, such as the esophagus,stomach, andintestines.[24] The esophagus develops as part of the foregut tube.[24] The innervation of the esophagus develops from thepharyngeal arches.[5] Nerve supply to upper two-third is from vagus and to lower one-third is from autonomic plexus.[23]
Food isingested through themouth and whenswallowed passes first into thepharynx and then into the esophagus. The esophagus is thus one of the first components of thedigestive system and thegastrointestinal tract. After food passes through the esophagus, it enters the stomach.[11] When food is being swallowed, theepiglottis moves backward to cover thelarynx, preventing food from entering thetrachea. At the same time, the upper esophageal sphincter relaxes, allowing abolus offood to enter.Peristaltic contractions of the esophageal muscle push 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 peristalsis, the lower esophageal sphincter relaxes.[11]
The stomach producesgastric acid, a stronglyacidic mixture consisting ofhydrochloric acid (HCl) andpotassium andsodium salts to enable fooddigestion. Constriction of the upper and lower esophageal sphincters helps to prevent reflux (backflow) of gastric contents and acid into the esophagus, protecting the esophageal mucosa. The acuteangle of His and the lowercrura of the diaphragm also help this sphincteric action.[11][25]
About 20,000 protein-coding genes are expressed in human cells and nearly 70% of these genes are expressed in the normal esophagus.[26][27] Some 250 of these genes are more specifically expressed in the esophagus with less than 50 genes being highly specific. The corresponding esophagus-specific proteins are mainly involved in squamous differentiation such askeratinsKRT13,KRT4 andKRT6C. Other specific proteins that help lubricate the inner surface of esophagus aremucins such asMUC21 and MUC22. Many genes with elevated expression are also shared with skin and other organs that are composed ofsquamous epithelia.[28]
Inflammation of the esophagus is known asesophagitis.Reflux ofgastric acids from the stomach, infection, substances ingested (for example,corrosives), somemedications (such asbisphosphonates), andfood allergies can all lead to esophagitis.Esophageal candidiasis is an infection of the yeastCandida albicans that may occur when a person isimmunocompromised. As of 2021[update] the causes of some forms of esophagitis, such aseosinophilic esophagitis, are not well-characterized, but may includeTh2-mediatedatopies or genetic factors. There appear to be correlations between eosinophilic esophagitis,asthma (itself with aneosinophilic component),eczema, andallergic rhinitis, though it is not clear whether these conditions contribute to eosinophilic esophagitis or vice versa, or if they are symptoms of mutual underlying factors.[29] Esophagitis can causepainful swallowing and is usually treated by managing the cause of the esophagitis - such as managing reflux or treating infection.[6]
There are two main types ofcancer of the esophagus.Squamous cell carcinoma is acarcinoma that can occur in the squamous cells lining the esophagus. This type is much more common inChina andIran. The other main type is anadenocarcinoma that occurs in the glands or columnar tissue of the esophagus. This is most common indeveloped countries in those with Barrett's esophagus, and occurs in the cuboidal cells.[6]
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 isstaged using a system that measures how far into the esophageal wall the cancer has invaded, how manylymph nodes are affected, and whether there are anymetastases in different parts of the body. Esophageal cancer is often managed with radiotherapy, chemotherapy, and may also be managed bypartial surgical removal of the esophagus. Inserting astent into the esophagus, or inserting anasogastric tube, may also be used to ensure that a person is able to digest enough food and water. As of 2014[update], the prognosis for esophageal cancer is still poor, sopalliative therapy may also be a focus of treatment.[6]
Esophageal varices are swollen twisted branches of theazygous vein in the lower third of the esophagus. These blood vesselsanastomose (join up) with those of theportal vein whenportal hypertension develops.[30] 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 theabdomen as a result ofportal hypertension, usually as a result ofliver diseases such ascirrhosis.[6]: 941–42 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.[7][8]
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 personto vomit blood, or suffershock. To deal with a ruptured varix, a band may be placed around the bleeding blood 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.IV fluids andblood products may be given in order to preventhypovolemia from excess blood loss.[6]
Several disorders affect the motility of food as it travels down the esophagus. This can cause difficult swallowing, calleddysphagia, or painful swallowing, calledodynophagia.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 eventualmegaesophagus. Anutcracker esophagus refers to swallowing that can be extremely painful.Diffuse esophageal spasm is a spasm of the esophagus that can be one cause of chest pain. Suchreferred pain to the wall of the upper chest is quite common in esophageal conditions.[31] Sclerosis of the esophagus, such as withsystemic sclerosis or inCREST syndrome may cause hardening of the walls of the esophagus and interfere with peristalsis.[6]
Esophageal strictures are usually benign and typically develop after a person has hadreflux for many years. Other strictures may includeesophageal webs (which can also be congenital) and damage to the esophagus by radiotherapy, corrosive ingestion, or eosinophilic esophagitis. ASchatzki ring is fibrosis at the gastroesophageal junction. Strictures may also develop in chronicanemia, andPlummer-Vinson syndrome.[6]
Two of the most commoncongenital malformations affecting the esophagus are anesophageal atresia where the esophagus ends in a blind sac instead of connecting to the stomach; and anesophageal fistula – an abnormal connection between the esophagus and the trachea.[32] Both of these conditions usually occur together.[32] These are found in about 1 in 3500 births.[33] Half of these cases may be part of asyndrome where other abnormalities are also present, particularly of theheart orlimbs. The other cases occur singly.[34]
A mass seen during anendoscopy and anultrasound of the mass conducted during the endoscopy session.
AnX-ray ofswallowed barium may be used to reveal the size and shape of the esophagus, and the presence of any masses. The esophagus may also beimaged using a flexible camera inserted into the esophagus, in a procedure called anendoscopy. If an endoscopy is used on the stomach, the camera will also have to pass through the esophagus. During an endoscopy, abiopsy may be taken. If cancer of the esophagus is being investigated, other methods, including aCT scan, may also be used.[6]
The wordesophagus (British English:oesophagus), comes from theGreek:οἰσοφάγος (oisophagos) meaninggullet. It derives fromtwo roots(eosin) to carry and (phagos) to eat.[35] The use of the word esophagus, has been documented in anatomical literature since at least the time ofHippocrates, who noted that "the oesophagus ... receives the greatest amount of what we consume."[36] Its existence in other animals and its relationship with thestomach was documented by theRomannaturalistPliny the Elder (AD23–AD79),[37] and theperistaltic contractions of the esophagus have been documented since at least the time ofGalen.[38]
The first attempt at surgery on the esophagus focused in the neck, and was conducted in dogs byTheodore Billroth in 1871. In 1877Czerny carried out surgery in people. 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 controlesophageal cancer), had been conducted.[39]
Intetrapods, 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 somebirds, which regurgitate components to feed their young, it is extended towards the lower end to form acrop for storing food before it enters the true stomach.[41][42] Inruminants, animals with four chambered stomachs, a groove called thesulcus reticuli is often found in the esophagus, allowing milk to drain directly into the hind stomach, theabomasum.[43] In thehorse the esophagus is about 1.2 to 1.5 m (4 to 5 ft) in length, and carries food to the stomach. A muscular ring, called the cardiac sphincter, connects the stomach to the esophagus. This sphincter is very well developed in horses. This and the oblique angle at which the esophagus connects to the stomach explains why horses cannotvomit.[44] The esophagus is also the area of the digestive tract where horses may have the condition known aschoke.
The esophagus ofsnakes is remarkable for the distension it undergoes when swallowing prey.[45]
In most fish, the esophagus is extremely short, primarily due to the length of the pharynx (which is associated with thegills). However, some fish, includinglampreys,chimaeras, andlungfish, have no true stomach, so that the esophagus effectively runs from the pharynx directly to theintestine, and is therefore somewhat longer.[41]
The muscle of the esophagus in many mammals is initially striated but then becomes smooth muscle in the caudal third or so. Incanines andruminants, 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.[42]
Contrary to popular belief,[46] an adulthuman body would not be able to pass through the esophagus of awhale, which generally measures less than 10 cm (4 in) in diameter, although in largerbaleen whales it may be up to 25 cm (10 in) when fully distended.[47]
A structure with the same name is often found in invertebrates, includingmolluscs andarthropods, connecting the oral cavity with the stomach.[48] In terms of thedigestive system of snails and slugs, the mouth opens into an esophagus, which connects to the stomach. Because oftorsion, which is the rotation of the main body of the animal during larval development, the esophagus usually passes around the stomach, and opens into its back, furthest from the mouth. In species that have undergone de-torsion, however, the esophagus may open into the anterior of the stomach, which is the reverse of the usual gastropod arrangement.[49] There is an extensiverostrum at the front of the esophagus in all carnivorous snails and slugs.[50] In the freshwater snail speciesTarebia granifera, the brood pouch is above the esophagus.[51]
In thecephalopods, the brain often surrounds the esophagus.[52]
^Purves, Dale (2011).Neuroscience (5th ed.). Sunderland, MA: Sinauer. p. 341.ISBN978-0-87893-695-3.
^abcdefDrake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell (2005).Gray's anatomy for students. illustrations by Richard M. Tibbitts and Paul Richardson. Philadelphia: Elsevier/Churchill Livingstone. pp. 192–94.ISBN978-0-8089-2306-0.
^abPatti, MG; Gantert, W; Way, LW (October 1997). "Surgery of the esophagus. Anatomy and physiology".The Surgical Clinics of North America.77 (5):959–70.doi:10.1016/s0039-6109(05)70600-9.PMID9347826.
^Drake, Richard L.; Vogl, Wayne; Mitchell, Adam W.M. (2009).Gray's anatomy for students. illustrations by Richard M. Tibbitts and Paul Richardson. Philadelphia: Elsevier/Churchill Livingstone. p. 215.ISBN978-0-443-06952-9.
^abcdHall, Arthur C. Guyton, John E. (2005).Textbook of medical physiology (11th ed.). Philadelphia: W.B. Saunders. pp. 782–784.ISBN978-0-7216-0240-0.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Anthony DiMarino, Jr.; Stanley B. Benjamin, eds. (2002).Gastrointestinal disease : an endoscopic approach. section editors Firas H. Al-Kawas (2nd ed.). Thorofare, NJ: Slack. p. 166.ISBN978-1-55642-511-0.
^Richard M. Gore; Marc S. Levine, eds. (2010).High-yield imaging (1st ed.). Philadelphia: Saunders/Elsevier. p. 151.ISBN978-1-4557-1144-4.
^Barrett, Kim E. (2014).Gastrointestinal physiology (2nd ed.). New York: Mc Graw Hill. pp. Chapter 7: "Esophageal Motility".ISBN978-0-07-177401-7.
^Long, Richard G; Scott, Brian B, eds. (2005).Specialist Training in Gastroenterology and Liver Disease. Elsevier Mosby. pp. 25–26.ISBN978-0-7234-3252-4.
^abcChaurasia, B.D. (2013). "19".Human Anatomy. Vol. 2 (6th ed.). 4819/XI, Prahlad Street, 24 Ansari Road, Daryaganj, New Delhi 110002, India: CBS Publishers and Distributors. p. 255.ISBN978-81-239-2331-4.{{cite book}}: CS1 maint: location (link)
^abcdGary C. Schoenwolf (2009). "Development of the Gastrointestinal Tract".Larsen's human embryology (4th ed.). Philadelphia: Churchill Livingstone/Elsevier.ISBN978-0-443-06811-9.
^Uhlén, Mathias; Fagerberg, Linn; Hallström, Björn M.; Lindskog, Cecilia; Oksvold, Per; Mardinoglu, Adil; Sivertsson, Åsa; Kampf, Caroline; Sjöstedt, Evelina (23 January 2015). "Tissue-based map of the human proteome".Science.347 (6220): 1260419.doi:10.1126/science.1260419.ISSN0036-8075.PMID25613900.S2CID802377.
^Standring S, Borley NR, eds. (2008).Gray's anatomy : the anatomical basis of clinical practice. Brown JL, Moore LA (40th ed.). London: Churchill Livingstone. pp. 1163, 1177,1185–6.ISBN978-0-8089-2371-8.
^abcRomer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 344–345.ISBN978-0-03-910284-5.
^abcdHume, Ian D.; Stevens, C. Edward (2005).Comparative physiology of the vertebrate digestive system (1st pbk. ed.). Cambridge: Cambridge University Press. p. 15.ISBN978-0-521-61714-7.
^Kutsch, W; Breidbach, O (1994).The nervous systems of invertebrates : an evolutionary and comparative approach. Basel: Birkhäuser. p. 117.ISBN978-3-7643-5076-5.
