Saturday, 7 February 2015

OESOPHAGUS OF HUMAN DIGESTIVE SYSTEM: Location, structure, function & disorder.

The oesophagus carries food and liquid from the mouth to the stomach and the rest of the intestinal tract and is an important site of common gastrointestinal disorders.


The oesophagus is a muscular tube, beginning at the pharynxand ending at the stomach. It traverses the neck and thorax, where it lies close to the trachea, the great vessels and the left atrium of the heart. The upper opening of the oesophagus lies behind the opening of the larynx and is separated from it by the arytenoid folds.
The epiglottis, attached to the back of the tongue, can flap over the larynx, protecting it during swallowing and funnelling food towards the oesophagus. Just above the gastro-oesophageal junction, the oesophagus traverses a natural hiatusor gap in the diaphragm, to enter the abdomen. The walls of the oesophagus reflect the general organization of the intestinal wall.
The walls are formed from outside to inside by:
• adventitia or serosa;
• longitudinal muscle layer;
• circular muscle layer;
• submucosal layer;
• muscularis mucosae;
• mucosa and epithelium.
The muscle in the upper third is striated muscle and in the lower two-thirds, smooth muscle similar to the rest of the gut. The lower oesophageal muscle remains in tonic contraction and forms part of the loweroesophageal sphincter. The angulationof the oesophagus as it enters the stomach and the diaphragmatic muscle help to keep the lower oesophagus closed. The vagus nerve runs alongside the oesophagus and innervates oesophageal muscle directly and via intrinsic nerves in the myenteric nerve plexus located between the longitudinal and circular muscle layers, and the submucosal plexus. The submucosa contains lobulated glands that secrete lubricating material through small ducts that penetrate the epithelial surface.
The oesophageal epithelium is a tough, non-cornified stratified squamous epithelium, which changes abruptly to a non-stratified columnar epithelium at the gastro-oesophageal junction, known as the Z-line. Importantly, venous drainage of the oesophagus forms a submucosal venous plexusthat drains directly into the systemic venous circulation, avoiding the hepatic portal vein and liver. This plexus anastomoses with veins in the stomach that drain into the hepatic portal system. In portal hypertension, collateral veins divert gastric blood to the oesophageal veins, which enlarge and form varices.


The oesophagus conveys food, drink and saliva from the pharynx to the stomach, by peristalsis. Peristalsis comprises a coordinated wave of contraction behind the bolus of food, with relaxation ahead of it, propelling the food bolus forward. It is involuntary, resulting from intrinsic neuromuscular reflexes in the intestinal wall, independent of extrinsic innervation. However, external stimuli modify the frequency and strength of peristaltic activity throughout the intestine. Very strong peristaltic contractions can cause pain. In vomiting, peristaltic waves travel in the reverse direction, propelling food upward towards the mouth.

Common disorders 

Dysphagia is difficulty in swallowing and odynophagia is painful swallowing. Sensations arising from the oesophagus are usually felt retrosternally in the lower part of the centre of the chest. Heartburn describes a burning, unpleasant retrosternal sensation that may be caused by acid reflux from the stomach into the oesophagus. Obstruction to flow down the oesophagus causes dysphagia and may be complete, halting swallowing altogether, so that the patient cannot even swallow saliva and drools continually. Chronic obstruction may lead to aspirationof food into the larynx, causing pneumonia. Refluxed stomach acid reaching the larynx can cause inflammation, causing cough and a hoarse voice. Cancer of the oesophagus or trauma, caused, for example, by a fishbone, can create a fistulafrom the oesophagus to the trachea, which lies immediately anteriorly. This can lead to recurrent infection caused by bacteria in the oesophageal fluid (aspiration pneumonia).
The lower oesophageal sphincter is relatively weak; therefore, acid refluxis common even in health, but can be excessive, when it may cause oesophagitis. Chronic acid reflux can induce the epithelium to change from the normal squamous lining to a gastric or intestine-like columnar lining. This epithelial metaplasiais called Barrett’soesophagus and it increases the risk of developing adenocarcinoma of the oesophagus. The diaphragmatic hiatus through which the oesophagus passes from the thorax to the abdomen widens with age and it may allow the upper part of the stomach to herniate into the thorax. This is known as a sliding hiatus hernia, which increases the risk of reflux oesophagitis. The sliding is aggravated by obesity and lying flat in bed. Very powerful muscular contraction and peristalsis (dysmotility) can cause discomfort or pain. Progressive failure of peristalsis and a chronically hypertonic lower oesophageal sphincter, leading to a dilated, nonfunctioning oesophagus, is called achalasia. Forceful retching or vomiting can cause a Mallory–Weisstear in the oesophageal mucosa, which may bleed, causing (usually) self-limiting haematemesis.
By contrast, oesophageal varices formed in portal hypertension can bleed catastrophically. Infections of the oesophagus are rare. The most common is candidiasis, occurring in immuno compromised patients and those with diabetes mellitus. Squamous carcinoma of the oesophagus is particularly common in southern Africa and may relate to diet, smoking and carcinogens in the soil, as well to genetic factors. Adenocarcinoma, arising from Barrett’s oesophagus, is becoming more common in the Western world.


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