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The esophagus (American English) or oesophagus (British English), commonly known as the foodpipe or gullet, is an organ in vertebrates which consists of a fibromuscular tube through which food passes, aided by peristaltic contractions, from the pharynx to the stomach. In humans, the esophagus is usually 18–25 centimeters (cm) long. During swallowing the epiglottis tilts backwards to prevent food from going down the larynx. The esophagus travels behind the trachea and heart, passes through the diaphragm and empties into the cardia of the stomach. The word ''esophagus'' derives from the Greek word ''oisophagos'', which means "to carry to eat."〔 The wall of the esophagus from the 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 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 third. It has two muscular rings or sphincters 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 nerves via the sympathetic trunk and parasympathetic nerves 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 gastric reflux, cancer, prominent dilated blood vessels called varices that can bleed heavily, tears, constrictions, and disorders of motility. Clinical investigations include X-rays using barium, endoscopy, and CT scans. ==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 diaphragm, and into the stomach. In humans, the esophagus generally starts around the level of the sixth cervical vertebra (C6) behind the cricoid cartilage, enters the diaphragm at about the level of the tenth thoracic vertebra (T10), and ends at the cardia of the stomach, at the level of the eleventh thoracic vertebra (T11). The esophagus is usually about 25 cm (10 in) in length. Many blood vessels 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 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.〔 The venous drainage also differs along the course of the esophagus. The upper and lower parts of the esophagus drain into the azygos and hemiazygos veins, 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.〔 Lymphatically, the upper third of the esophagus drains into the deep cervical lymph nodes, the middle into the superior and posterior mediastinal lymph nodes, and the lower esophagus into the gastric and celiac lymph nodes.〔 The esophagus is innervated by the vagus nerve and the cervical and thoracic sympathetic trunk.〔 The vagus nerve has a 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.〔 The vagus nerve plays the primary role in initiating peristalsis. The sympathetic trunk has a 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.〔 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.〔 ;Position The upper esophagus lies at the back of the mediastinum behind the trachea, and in front of the erector spinae muscles and the vertebral column. The lower esophagus lies behind the heart and curves in front of thoracic aorta. From the 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.〔 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 veins and the intercostal veins on the right side. The vagus nerve divides and covers the esophagus in a plexus.〔 ;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:〔 * 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 diaphragm 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Esophagus」の詳細全文を読む スポンサード リンク
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