The oesophagus is a muscular tube, about 25cm long, with a sphincter (valve) at each end. Its function is to transport food and fluid, after being swallowed, from the mouth to the stomach. No absorption of nutrients takes place in the oesophagus. A mouthful of food which has been chewed and swallowed is called a bolus. This is propelled from the pharynx (throat) into the oesophagus, and is swept towards the stomach in peristaltic waves. These muscular contractions are involuntary, and cannot normally be felt. When food is not passing through, the oesophagus is folded in, or collapsed.
The sphincters at either end of the oesophagus are normally closed, acting as valves. The upper one, below the pharynx, opens upon swallowing to allow entry into the oesophagus. The lower one, at the entrance to the stomach, also only opens to allow food and fluid to pass through. This one - the gastro-oesophageal or lower oesophageal sphincter - plays an important role in stopping reflux of acidic stomach contents back into the oesophagus. Although mucus is produced in the oesophagus, it is not as protective as mucus in the stomach, and so is more susceptible to damage by gastric juice.