|The esophagus relations to pharynx and mouth|
|Digestive organs (esophagus is #1)|
|Gray's||subject #245 1144|
|System||Part of the Digestive system|
|Nerve||Celiac ganglia, vagus|
The esophagus (oesophagus, commonly known as the gullet) is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. The word esophagus is derived from the Latin œsophagus, which derives from the Greek word oisophagos, lit. "entrance for eating."
- 1 Structure
- 2 Function
- 3 Clinical significance
- 4 History
- 5 In other animals
- 6 See also
- 7 Additional images
- 8 References
- 9 External links
In humans the esophagus is continuous with the laryngeal part of the pharynx at the level of the C6 vertebra. The esophagus passes through posterior mediastinum in the thorax and enters abdomen through a hole in the diaphragm at the level of the tenth thoracic vertebrae (T10). It is usually about 25cm, but extreme variations have been recorded ranging 10–50 cm long depending on individual height. It is divided into cervical, thoracic and abdominal parts. Due to the inferior pharyngeal constrictor muscle, the entry to the esophagus opens only when swallowing or vomiting.
In animals, food is ingested through the mouth. During swallowing, food passes from the mouth through the pharynx into the esophagus. The epiglottis folds down to a more horizontal position so as to prevent food from going into the trachea, instead directing it to the esophagus. Once in the esophagus, the bolus travels down to the stomach via rhythmic contraction and relaxation of muscles known as peristalsis.
At rest, the esophagus is closed at both ends by the upper esophageal sphincter at the top, and the lower esophageal sphincter at the bottom.
The upper esophageal sphincter (also called the pharyngoesophageal sphincter) refers to the superior portion of the esophagus. Unlike the lower esophageal sphincter, it consists of skeletal muscle and yet, is not under conscious control. Opening of the UES is triggered by the swallow reflex. The primary muscle of the UES is the cricopharyngeus portion of the inferior pharyngeal constrictor. During swallowing, the upper esophageal sphincter opens so the bolus can pass into the esophagus. A secondary role of the UES is to reduce backflow from the esophagus into the pharynx. It also makes the sound of eructation.
The lower esophageal sphincter is a muscular sphincter surrounding the lower part of the esophagus. The junction between the esophagus and the stomach (the gastroesophageal junction or GE junction) is controlled by the lower esophageal sphincter (LES), which remains constricted at all times other than during swallowing and vomiting to prevent the contents of the stomach from entering the esophagus. As the esophagus does not have the same protection from acid as the stomach, any failure of the LES can lead to heartburn.
Normally, the esophagus has three anatomic constrictions at the following levels:
- At the esophageal inlet, where the pharynx joins the esophagus, behind the cricoid cartilage (14–16 cm from the incisor teeth).
- Where its anterior surface is crossed by the aortic arch and the left bronchus (25–27 cm from the incisor teeth).
- Where it pierces the diaphragm (36–38 cm from the incisor teeth).
The distances from the incisor teeth are important as is useful for diagnostic endoscopic procedures.
The oesophagus fails to develop or there is a fistula between the trachea and oesophagus in about 1 in 3500 births. Conventional classification divides such fistulas into five types, based on whether the oesophagus is a continuous tube or not, and which end of the oesophagus (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.
The esophagus has a mucosa consisting of a stratified squamous epithelium without keratin, a smooth lamina propria, and a muscularis mucosae of smooth muscle. The submucosa contains the mucous secreting glands (esophageal glands), and connective structures termed papillae. The muscularis externa has a unique composition, varying over the length of the esophagus. The upper third of the muscularis is striated muscle, the middle third both smooth muscle and striated muscle, and the lower third predominantly smooth muscles. The esophagus also has an adventitia.
On histological examination, the junction can be identified the transition between nonkeratinized stratified squamous epithelium in the esophagus, and simple columnar epithelium in the stomach.  The z-line is defined as this point, and the cardia of the stomach as the area immediately distal to the z-line.  This junction usually occurs in the area of the oesphagus surrounded by the lower oesophageal sphincter, and is characterised macroscopically by changes from salmon pink to a deeper red. But, a study correlating manometric and endoscopic localization of the LES (z-line) found that the functional location of LES was 3 cm distal to the z-line. 
In Barrett's esophagus, the epithelial distinction may vary, so the histological border may not be identical with the functional border. The cardiac glands can be seen in this region. They can be distinguished from other stomach glands (fundic glands and pyloric glands) because the glands are shallow and simple tubular.
Section from the middle of the human esophagus.; a. Fibrous covering.; b. Divided fibers of longitudinal muscular coat.; c. Transverse muscular fibers.; d. Submucous or areolar layer.; e. Muscularis mucosae.; f. Mucous membrane, with vessels and part of a lymphoid nodule.; g. Stratified epithelial lining.; h. Mucous gland.; i. Gland duct.; m’. Striated muscular fibers cut across.
The oesophagus develops from the embryonic gut tube, an endodermal 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 oesophagus, stomach, and intestines. 
The sac is surrounded by a network of arteries called the vitellline plexus. Over time, these arteries consolitate into three main arteries that supply the developing gastrointestinal tract: the coeliac artery, superior mesenteric artery, and inferior mesenteric artery. The areas supplied by these arteries are used to define the midgut, hindgut and foregut. 
The oesophagus develops as part of the foregut tube. 
In the esophagus, as in much of the gastrointestinal tract, smooth muscles contract in sequence to produce a peristaltic wave which forces a ball of food (called a bolus) down and through the LES into the stomach.
The stomach generates strong acids (HCl) and enzymes (such as pepsin) to aid in food digestion. This digestive mixture is called gastric juice. The inner lining of the stomach has several mechanisms to resist the effect of gastric juice on itself, but the mucosa of the esophagus does not. The esophagus is normally protected from these acids by a one-way valve mechanism at its junction with the stomach. This one-way valve is called the esophageal sphincter (ES), and this, along with the angle of His formed here, prevents gastric juice from flowing back into the esophagus.
During peristalsis, the oesophageal sphincter allows the food bolus to pass into the stomach. It prevents chyme, a mixture of bolus, stomach acid, and digestive enzymes, from returning up the esophagus. The oesophageal sphincter is aided in the task of keeping the flow of materials in one direction by the diaphragm.
The esophageal sphincter is a functional sphincter but not an anatomical sphincter. That is to say, though there is no thickening of the smooth muscle, as in the pyloric sphincter, chyme is (usually) prevented from travelleling back from the stomach up the esophagus. The lower crus of the diaphragm helps this sphincteric action. 
Inflammation of the esophagus is known as esophagitis. Substances ingested (for example, corrosives), some medications (such as Bisphosphinates), food allergies, infection, and reflux of gastric acids from the stomach can all lead to esophagitis. As of 2014[update] the cause of some forms of esophagitis, such as eosinophilic esophagitis, is not known. Esophagitis can cause painful swallowing and is usually treated by managing the cause of the oesophagitis - such as managing reflux or treating infection.  :863-867
Prolonged oesophagitis, particularly from gastric reflux, is one factor thought to play a role in the development of Barrett's oesophagus. In this condition, the lining of the oesophagus changes from multiple layers of flat cells to a single layer of taller, secretory cells. The new cells are known as cuboidal epithelia and are the same as the lining of the stomach. Barrett's oesophagus is thought to be one of the main contributors to the development of esophageal cancer. :863-867
Cancer of the oesophagus differs geographically. In some countries, such as China and Iran, cancer of the flat cells lining the oesophagus is common. In Western countries, oesophageal cancer is more common in people who already have Barrett's esophagus, and occurs in the cuboidal cells. In its early stages, oesophageal cancer may not have any symptoms at all. When severe, esophageal cancer may eventually cause obstruction of the oesophagus, making swallowing of any solid foods very difficult and causing weight loss. The progress of the cancer is staged using a system that measures how far into the oesophageal wall the cancer has invaded, how many lymph nodes possess the cancer, and whether there are any metastases in different parts of the body. Oesophageal cancer is often managed with radiotherapy, chemotherapy, and may also be managed by partial surgical removal of the esophagus. Inserting a stent into the oesophagus, or inserting a nasogastric tube, may also be used to ensure that a person is able to digest enough food and water. Unfortunately, As of 2014[update] the prognosis for oesophageal cancer is still poor, so palliative therapy may also be a focus of treatment.  :869-870
Oesophageal varices refer to engorged blood vessels visible within the oesophageal walls. These blood vessels are engorged more than normal, and in the worst cases may partially obstruct the oesophagus. 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 diseases such as cirrhosis. Oesophageal varices often do not have symptoms until they rupture. A ruptured varice is considered a medical emergency, because varices can bleed a lot. A bleeding varice may cause a person to throw up blood, or may cause symptoms of hypovolemic shock. To deal with a ruptured varice, 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 to ensure that they don't become dehydrated.  :941-942
An X-ray of swalloed barium may be used to reveal the size and shape of the esophagus, and whether there are any masses. The oesophagus may also be imaged using a flexible camera inserted into the esophagus, called an endoscopy. If the stomach undergoes endoscopy, the camera will also have to pass through the esophagus. During an endoscopy, a biopsy maybe taken. If cancer of the oesphagus is being investigated, other tests, such as a CT scan, may also be used. :860-870
Deficiencies in the strength or the efficiency of the LES lead to various medical problems involving acid damage on the esophagus.
|This section requires expansion. (December 2013)|
In other animals
In most fish, the esophagus is extremely short, primarily due to the length of the pharynx (which is associated with the gills). However, some fish, including lampreys, chimaeras, and lungfish, have no true stomach, so that the esophagus effectively runs from the pharynx directly to the intestine, and is therefore somewhat longer.
In tetrapods, the pharynx is much shorter, and the esophagus correspondingly longer, than in fish. In amphibians, sharks and rays, the esophageal epithelium is ciliated, helping to wash food along, in addition to the action of muscular peristalsis. In the majority of vertebrates, the esophagus is simply a connecting tube, but in birds, it is extended towards the lower end to form a crop for storing food before it enters the true stomach.
- Physiology at MCG 6/6ch2/s6ch2_30
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- BU Histology Learning System: 10801loa
- BU Histology Learning System: 11101loa
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