2015B12 Describe the physiological factors that contribute to the competence and
tone of the lower oesophageal sphincter.

 

List:

·       Intro

·       Anatomy

·       Neural control

·       Physical factors

·       Hormonal factors

 

Intro:

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

 

Anatomy:

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

 

Neural control:

Innervation

·  Meissner’s submucosal plexus

·  Auerbach’s myenteric plexus (between circular and longitudinal layers)

Intrinsic

·  Myenteric reflex: distension > peristalsis (e.g. swallowing)

·  Myogenic reflex: distension -> contraction

Extrinsic

·  PSNS: CNX via oesophageal plexus

·  SNS: cervical and thoracic SNS trunk via oesophageal plexus

·  Complex modulation of intrinsic circuits

 

Physical factors:

Gravity

·  Trendelenburg positioning -> ↑regurgitation

Pressure

·  ↑Abdo pressure -> ↓barrier pressure

o Obesity

o Pregnancy

o Laparoscopy

Sphincter

·  e.g. hiatus hernia -> ↓LOS competence

 

Hormonal factors:

↑ LOS tone

·  Gastrin

·  CCK

·  Motilin

·  Oestrogen

↓LOS tone

·  Progesterone (i.e. pregnancy)

·  VIP (causes reflex relaxation after swallowing)

·  GIP

·  Secretin

·  PGE2

·  Glucagon

·  Severe illness

 

 

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