Overview
The esophagus (oesophagus) begins dorsal to the cricoid cartilage of the larynx. In the neck it first runs dorsal to the trachea and then on its left, so the passage of a bolus can be seen in the left jugular groove. In the thorax it runs through the mediastinum, dorsal to the trachea and the heart base, crosses the diaphragm through the esophageal hiatus and opens soon after at the cardia, at the junction of the reticulum and the ruminal atrium.
Structure
- Muscular coat: in ruminants it is striated muscle along its whole length, which allows rapid transport in both directions.
- Mucosa: stratified squamous epithelium with longitudinal folds that flatten when it distends.
- Reticular groove: begins at the cardia and continues the line of the esophagus to the reticulo-omasal orifice.
Function in the ruminant
- Rumination: the esophagus returns boluses from the reticulorumen to the mouth to be chewed and mixed with saliva again, and then swallows them again.
- Eructation: fermentation gases are expelled through the esophagus; part of the gas passes into the lungs before leaving.
Clinical relevance
- Esophageal obstruction (choke): whole fruits and tubers (potatoes, apples, beets) usually lodge in the cervical part, at the thoracic inlet or over the heart base. It causes drooling, attempts to swallow and free-gas bloat, because the animal cannot eructate.
- Tubing: the orogastric tube is used to give fluids and drugs, relieve bloat and collect rumen fluid; its position is checked by palpating it in the left jugular groove or by blowing and listening over the rumen.
- Compression: enlarged mediastinal lymph nodes or abscesses can compress the esophagus and cause chronic bloat.
- Bovine viral diarrhoea (mucosal disease): causes erosions and ulcers in the esophageal mucosa, as well as in the mouth and the rest of the digestive tract.