Overview
The oesophagus starts dorsal to the cricoid cartilage, over the larynx. In the neck it first runs dorsal to the trachea and, from the middle third on, lies on its left side, deep in the left jugular groove. At the thoracic inlet it returns to the dorsal surface of the trachea, crosses the base of the heart in the mediastinum and passes through the diaphragm at the oesophageal hiatus. The abdominal part is very short and ends at the cardia.
Structure
- Muscular coat: striated in the cranial two-thirds and smooth in the caudal third, where the wall thickens and the lumen narrows.
- Mucosa: stratified squamous epithelium, with longitudinal folds that flatten as the bolus passes.
- Cardia: the oesophagus enters the stomach obliquely, and the muscle of the cardia forms a powerful sphincter. Together with the position of the stomach under the ribs, this means that horses can hardly vomit or belch.
Clinical relevance
- Oesophageal obstruction (choke): a bolus of dry feed (pellets, unsoaked beet pulp) or a foreign body lodges, often in the neck or at the thoracic inlet. The horse discharges saliva and food from both nostrils, coughs, stretches its neck and may show a swelling in the left jugular groove. The main complication is aspiration pneumonia.
- Strictures: after an obstruction with circumferential mucosal damage, scar strictures may form and predispose to new obstructions; they are monitored by endoscopy.
- Nasogastric intubation: the tube is passed through the ventral nasal meatus; in the oesophagus it is seen or felt in the left jugular groove and meets resistance as it advances, whereas in the trachea it slides in without resistance and vibrates with breathing.