NORMAL OESOPHAGUS

The oesophagus is a muscular tube connecting the oropharynx to the stomach. It begins at the lower margin of the cricopharyngeous muscle and is approximately 25cm long. It is composed of striated muscle in the upper third, smooth muscle in the lower two thirds, and is lined throughout by squamous epithelium.

In the mediastinum, the oesophagus is closely related to the two trunks of the vagus nerve, the trachea, the aorta and the heart. Both aortic and left bronchial impressions can be visualized during a barium swallow examination.

In addition to demonstrating the normal mucosal pattern of the oesophagus, a barium swallow may show a slight constriction approximately 2cm above the diaphragm, below which is an area of dilatation known as the vestibule, or phrenic ampulla. This area of dilatation should not be confused with the radiological appearances of hiatus hernia.

The oesophagus enters the stomach at an oblique angle just below the diaphragmatic crura approximately 40cm from the incisor teeth.

Food is transported from the pharynx to the stomach by co-ordinated contraction of the muscular layers of the body of the oesophagus. This peristaltic contraction wave is relatively slow and moves down the oesophagus at a rate of 2-6cm per second. When initiated by swallowing, it is known as primary peristalsis, as distinct from secondary peristalsis, which originates below the hypopharynx with no antecedent swallowing movement.

The barrier functions of the oesophagus depend on the upper cricopharyngeal and lower oesophageal sphincters (LOS). The LOS is a zone of high pressure (normally between 15 and 35mmHg) extending over the lowest 3-4cm of the oesophagus; it has no definite anatomical counterpart.

Manometric studies of oesophageal motility are readily accomplished using a transnasal catheter. On swallowing, the normal upper sphincter relaxes before passage of the bolus and then contracts; this is followed by a peristaltic contraction along the body of the oesophagus, and the LOS relaxes just prior to the contraction wave reaching it, thus allowing passage of the bolus into the stomach.

The LOS alone is not, however, sufficient to prevent gastro-oesophageal reflux, but is aided by compression of the subdiaphragmatic portion of the oesophagus as a result of a rise in intragastric or intra-abdominal pressure. The acute angle of entry of the oesophagus into the stomach is an additional protective factor.

The pH within the oesophagus is usually 5-7, unless there is reflux of acidic gastric contents. A pH of less than 4 is normally considered pathological, though it occurs for brief periods in normal subjects; assessment is best made by continuous 24 hour pH monitoring.

Endoscopically, the body of the oesophagus appears as a smooth featureless tube with visible submucosal blood vessels. At the gastro-oesophageal junction, the transition from oesophageal to gastric mucosa is easily seen as an irregular circumferential line known as the ora serrata, gastric rosette, or Z-line. Peristaltic waves will often be seen during the examination.

The luminal surface of the oesophagus is lined by non-keratinized squamous epithelium. Papillae, which are extensions of the lamina propria, penetrate for a short distance into the epithelium. The lamina propria is separated from the underlying submucosa by a thin layer of smooth muscle, the muscularis mucosae. Deep to the submucosa is the circular muscle layer, the myenteric plexus lying between this and the deeper longitudinal muscle.