||It has been suggested that Upper_esophageal_sphincter be merged into this article. (Discuss) Proposed since October 2013.|
|This article needs additional citations for verification. (December 2007)|
|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."
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.
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.
The layers of the oesophagus are as follows:
- submucosa: Contains the mucous secreting glands (esophageal glands), and connective structures termed papillae.
- muscularis externa (or "muscularis propria"): composition varies in different parts of the esophagus, to correspond with the conscious control over swallowing in the upper portions and the autonomic control in the lower portions:
- fibroareolar adventitia
Similar to rectum, it lacks serosa
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 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.
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.
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.
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