The oesophagus connects the buccal cavity with the stomach. The stratified squamous non-keratinised epithelium lining the buccal cavity is continued through the pharynx down into the oesophagus. The lowest part of the oesophagus is lined with gastric mucosa and covered by peritoneum. The main body of the oesophagus is lined with small, simple mucous glands. Each gland opens into the lumen by a long duct which pierces the muscularis mucosae (Wilson and Washington, 1989). A sphincter is situated at the point where the oesophagus enters the stomach to prevent gastro oesophageal reflux, i.e. to prevent acidic gastric contents from reaching stratified epithelia of the oesophagus, where they can cause inflammation and irritation (Wilson and Washington, 1989; Brown et al., 1993). 

Morphologically the oesophagus is similar in man and pig; both are omnivores and have a non-keratinised epithelium, submucous glands and similar membrane enzymes. 

Like in humans, pigs can suffer from reflux oesophagitis and stress ulceration of the oesophagus. The pig oesophagus may therefore be a good model for investigation compared to the human oesophagus (Christie et al., 1995).

The human oesophagus

In humans, the pH of the normal oesophagus lumen is usually between 5 and 6. Mucous with a pH of 5 – 6 is secreted into the oesophagus for easy gliding of food. With mucus, also bicarbonate and epidermal growth factor are secreted, which together with bicarbonate present in saliva, protect the lower part of the oesophagus for the acid gastric juice (Wilson and Washington, 1989; Brown et al., 1993). Liquid passes directly, but for instance capsules taken without water can stick to the oesophagus wall for 2 h.