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The oesophagus is a muscular tube that connects the back of the throat to the stomach. It is part of the digestive system and is located in the centre of the chest, behind the windpipe. The oesophagus has two sphincters, or circular bands of muscle, at either end: the upper oesophageal sphincter (UES) and the lower oesophageal sphincter (LES). These sphincters sense when food is passing through and relax to let it pass into the stomach. The oesophagus also has longitudinal muscle fibres, which help reduce the tension of circular muscle contractions. The oesophagus is made up of four layers, one of which is a muscle layer called the muscularis propria.
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What You'll Learn
The oesophagus is a hollow, muscular tube
The oesophagus is a muscular tube that connects the back of the throat to the stomach. It is a hollow structure, allowing food and drink to pass through and enter the stomach. The oesophagus is located behind the trachea, in the centre of the chest, and is part of the digestive system.
The oesophagus has a number of muscles, including the upper esophageal sphincter (UES) and the lower esophageal sphincter (LES). The UES and LES act as valves, opening to allow food and liquid to pass through and then closing to prevent stomach acid and digestive juices from entering the oesophagus. The UES and LES are composed of smooth muscle fibres, which contract and relax to open and close the sphincters. The LES, in particular, has smooth muscles that help keep the sphincter tightly closed, protecting the oesophagus from stomach acid.
The oesophagus itself consists of four layers: mucosa, submucosa, muscularis propria, and adventitia or serosa. The muscle layer, or muscularis propria, is further divided into an outer longitudinal muscle layer and an inner circular muscle layer. The longitudinal muscles help reduce the tension associated with circular muscle contractions, which aids in peristaltic movements. The circular muscles, on the other hand, contract radially to propel food downwards through the oesophagus and into the stomach.
The upper third of the oesophagus contains striated muscle, followed by a zone of overlap with smooth muscle. The distal two-thirds of the oesophagus are formed solely by smooth muscle. The oesophageal muscles in the upper portion, used for swallowing, are under voluntary control. The remaining portion, composed of smooth muscle, is not under voluntary control.
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The oesophagus has two sphincters
The oesophagus is a fibromuscular tube that is part of the digestive system. It is a hollow structure that connects the pharynx to the stomach, allowing food and liquid to pass through. The oesophagus has two sphincters, the upper and lower oesophageal sphincters (UES and LES, respectively), which are located at the openings of the oesophagus. These sphincters are ring-shaped muscles that act as valves, controlling the passage of food and liquid into the oesophagus and preventing the backflow of stomach contents.
The UES is a high-pressure zone found at the transition between the pharynx and the cervical oesophagus. It senses the presence of food and liquid, relaxing to allow their passage and contracting when no food is present to prevent the backflow of stomach acid and digestive juices. The UES is composed of striated muscle fibres and is supplied by fibres originating from the nucleus ambiguus.
The LES, on the other hand, is located where the oesophagus meets the stomach. It also has a high-pressure zone and serves to protect the oesophagus from the reflux of gastric contents, including stomach acid. The LES consists of smooth muscles that contract to keep the sphincter tightly closed. In response to inhibitory signals, such as swallowing, the smooth muscles relax, allowing the sphincter to open and food to pass through. The LES does not possess dilator muscles, and its opening depends solely on the relaxation of the smooth muscles. The LES is supplied by fibres arising from the dorsal motor nucleus.
Both sphincters play a crucial role in the proper functioning of the oesophagus. Any malfunction or disease affecting these sphincters can lead to various oesophageal conditions, such as gastroesophageal reflux disease (GERD) and achalasia. GERD is a chronic disorder characterised by the backflow of stomach acid into the oesophagus, resulting in symptoms like heartburn, chest pain, and hoarseness. Achalasia is a rare disorder where the LES fails to open when it should, preventing food from reaching the stomach.
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The oesophagus has four layers
The oesophagus, also known as the food pipe, food tube, or gullet, is a fibromuscular tube that connects the pharynx to the stomach. It is a part of the digestive system and is located behind the trachea, extending from the neck to the abdomen. The oesophagus has four distinct layers, each serving a specific function:
The innermost layer of the oesophagus is called the mucosa. It is a tough, stratified squamous epithelium that acts as a protective barrier against the abrasive effects of food. The mucosa consists of three sublayers: the mucous membrane, the lamina propria, and the muscularis mucosa. The mucous membrane is composed of squamous and columnar epithelial cells, which cover the inner surface of the oesophagus. The lamina propria is a smooth layer that provides support to the mucous membrane. The muscularis mucosa is a thin layer of irregularly arranged smooth muscle fibres.
The second layer of the oesophagus is the submucosa. It contains mucus-secreting glands that produce mucus to protect the lining of the oesophagus. The submucosa also houses the submucosal plexus, a network of nerve cells that is a part of the enteric nervous system.
The third layer is the muscularis propria, which is primarily responsible for the movement of food through the oesophagus. This layer consists of two types of muscles: an outer longitudinal layer and an inner circular layer. The longitudinal muscles help reduce the tension associated with circular muscle contractions, augmenting peristaltic movements. The circular muscles, on the other hand, contract radially to propel food downwards towards the stomach.
The outermost layer of the oesophagus is the adventitia or serosa, depending on the region of the oesophagus. In most parts of the oesophagus, the adventitia forms the outer layer, consisting of connective tissue. However, in the distal and intraperitoneal portions of the oesophagus, there is an outer covering of serosa instead of adventitia.
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Smooth muscle differentiation in the oesophagus
The oesophagus is a muscular tube that carries food and liquid from the throat to the stomach. It is composed of four layers: the mucosa, submucosa, muscularis propria, and adventitia or serosa. The muscularis propria, or muscle layer, is further divided into an outer longitudinal and an inner circular layer. The oesophagus is unique in that it is made up of both skeletal and smooth muscles. The upper third of the oesophagus contains striated muscle, followed by a zone of overlap with smooth muscle, while the lower two-thirds are formed by smooth muscle alone.
The smooth muscle differentiation process in the oesophagus has been a subject of debate for many years. Initially, it was proposed that smooth muscle cells (SMCs) directly transdifferentiated into skeletal muscle cells. However, immunohistochemistry and ultrastructural studies indicated the presence of two separate precursor cell populations. Lineage tracing with a SMC-specific Cre transgene in mice proved that ESMs did not derive from SMCs. Instead, it was found that pharyngeal mesoderm-derived, Isl1+ progenitor cells seed the proximal portion of the oesophagus and then migrate towards the anterior end, differentiating in a "transition zone" near the migratory front.
The oesophageal smooth muscle layer is important for several functions. It helps to regulate the lower oesophageal sphincter (LES), which is composed entirely of smooth muscles. The LES remains tightly closed, preventing stomach acid and digestive juices from entering the oesophagus. In response to inhibitory signals, the smooth muscles in the LES relax, allowing food to pass through to the stomach. The pressure in the LES is determined by the myogenic tone of the smooth muscles, as well as the presence of inhibitory nitrergic nerves and excitatory cholinergic nerves. The myogenic tone is an intrinsic property of the smooth muscle cells, leading to spontaneous contractions.
The smooth muscle layer also has sensory functions. Vagal afferent neurons merging from the oesophageal smooth muscle layer are sensitive to mechanical distension, while those with receptive fields in the mucosa respond to various osmo-, chemo-, thermo-, and mechanical intraluminal stimuli. These vagal afferents can transduce pressure into painful sensations.
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Oesophageal motility disorders
The oesophagus is a muscular tube that carries food and liquid from the throat to the stomach. It is composed of four layers: mucosa, submucosa, muscularis propria, and adventitia or serosa. The muscularis propria layer is further divided into an outer longitudinal and an inner circular muscular layer. The oesophageal body comprises two types of muscles: striated muscles in the proximal portion and smooth muscles in the distal portion. The transition from skeletal to smooth muscles occurs in the mid-oesophagus.
One of the most common symptoms of oesophageal motility disorders is chest pain, which may occur before or after swallowing or at random times. Other symptoms include regurgitation, difficulty swallowing (dysphagia), heartburn, hoarseness or sore throat, vomiting or vomiting blood, bad breath (halitosis), and weight loss. Diagnosis of oesophageal motility disorders typically involves a thorough physical examination, a review of the patient's history, and the elimination of other potential causes for the symptoms. Tests such as oesophageal manometry, esophagoscopy, upper endoscopy, barium swallow, biopsy, and acid- and reflux-related tests may also be ordered.
Treatment for oesophageal motility disorders depends on the specific type of disorder. Lifestyle changes, such as eating smaller, more frequent meals and softer foods, can help reduce pressure on the lower oesophageal sphincter. Medications, such as acid-suppressing drugs, may also be prescribed. In some cases, surgery, such as Heller myotomy or oesophageal dilation, may be necessary to correct the disorder.
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Frequently asked questions
Yes, the esophagus is a hollow muscular tube that connects the back of the throat to the stomach. It has both smooth and skeletal muscles.
The muscles in the esophagus help propel food down to the stomach. The upper muscles, used for swallowing, are under voluntary control. The lower esophageal sphincter (LES) is a ring-shaped muscle that senses when food is passing through and relaxes to let it through to the stomach. It also stays shut to prevent stomach acid from entering the esophagus.
The wall of the esophagus consists of four layers: mucosa, submucosa, muscularis propria (the muscle layer), and adventitia/serosa. The muscle layer further divides into an outer longitudinal and an inner circular muscular layer.
