A. Has no tonic activity
B. Has a tone which is provided by the sympathetic system
C. Relaxes on increasing abdominal pressure
D. Relaxes ahead of the peristaltic wave
Answer is D. Relaxes ahead of the peristaltic wave.
The lower 3-4 cms of the oesophagus is thickened to form Lower Oesphageal Sphincter. The smooth circular muscle fibres of gastro-oesophageal junction is thickened to form lower oesophageal sphincter. It is not a true anatomic sphincter.
- Lower oesophageal sphincter definitely has a tone.
- Lower oesophageal sphincter tone is under parasympathetic neural control and not sympathetic system as in the question. It has vagal excitatory and vagal inhibitory fibres.
- Vagal Excitatory Fibres (VEF): Causes release of Acetylcholine and oesophageal sphincter contraction.
- Vagal Inhibitory Fibres (VIF): Causes release of NO and VIP resulting in relaxation of lower oesophageal sphincter.
- Lower oesophageal sphincter tone is also influenced by some gastrointestinal hormones and endocrinal mechanisms.
- When the peristaltic swallowing wave passes down the oesphagus there is receptive relaxation of the lower oesophageal sphincter ahead of the peristaltic wave, which propels the food into the stomach.
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