· Intro
· Anatomy
· Neural factors
· Hormonal factors
· Other physical factors
Importance |
· Prevents regurgitation and aspiration · Especially important supine, under anaesthesia |
Barrier pressure |
· Barrier pressure = sphincteric – intragastric · Normal pressures (cmH2O): barrier 26, sphincter 36, intragastric 10 · Reflux occurs when barrier pressure <13cmH2O |
Inner sphincter |
· Lower 2-4cm oesophagus. Not anatomically distinct, not a true sphincter. · Tonic contraction of circular muscle · Provides 90% of basal pressure · Innervation: CNX, abundant |
Outer sphincter |
· Right crus of diaphragm loops contralaterally around lower oesophagus. “Pinch cock” mechanism · Intermittent contraction · Applies co-ordinated pressure during inspiration, coughing · Inervation: phrenic |
Oblique entry |
· Oblique passage of oesophagus into stomach · Gastric distension -> closure of orifice · “Flap-valve” mechanism |
Intra-abdominal position |
· Sphincter is intra-abdominal · External pressure assists closure |
Intrinsic |
· Meissner’s submucosal plexus · Auerbach’s myenteric plexus: between circular and longitudinal layers · Myenteric reflex: distension > peristaltic wave (sensed and
controlled by the above). · Myogenic reflex: distension -> contraction · Swallowing: ↑VIP -> reflex relaxation |
Extrinsic |
· PSNS: CNX via oesophageal plexus. · SNS: cervical and thoracic SNS trunk via oesophageal plexus. · Complex modulation of intrinsic circuits |
↑ LOS tone |
· Gastrin · CCK · Motilin · Oestrogen |
↓LOS tone |
· Secretin · GIP · VIP · Progesterone · PGE2 · Glucagon · Severe illness ? exact cause |
Intra-abdominal hypertension |
· ↑Abdo pressure -> ↓barrier pressure o Obesity, pregnancy o Reverse Trendelenburg position o Laparoscopy |
Sphincter dysfunction |
· e.g. hiatus hernia -> ↓LOS competence |
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