Lower Oesophageal Sphincter
Figure 4.3 Progression of a peristaltic wave through the oesophagus interrupted by the second peristaltic wave. When swallows are repeated in quick succession, then the contraction of the oesophagus is inhibited until the last swallow occurs; only the final peristaltic wave proceeds uninterrupted to the cardia carrying any food bolus or drug formulation with it.
If the subject is upright, gravity assists the movement of the swallowed material which may arrive at the lower oesophageal sphincter before relaxation has begun. This is especially true for non-viscous liquids whose entry in stomach may be slightly delayed until the lower oesophageal sphincter relaxes. Secondary peristaltic waves arise from distension of the oesophagus and serve to move sticky lumps of food or refluxed materials into the stomach. Initiation of secondary peristalsis is involuntary and is not normally sensed. Variation in the size of the bolus being swallowed leads to a variation in the amplitude of oesophageal contraction.
The pH of the oesophagus is between 6 and 7. After a meal, reflux of gastric acid is seen as sharp drops in pH which rapidly return to baseline. This is a normal physiological occurrence. Gastro-oesophageal reflux disease (heartburn) occurs when gastric acid damages the oesophageal mucosa either through prolonged contact or reduced resistance of the mucosa to damage.
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