GIT – Motility

Master answer

• Main barrier to reflux is the lower oesophageal sphincter (LOS).
• Sphincter pressure maintained at 15-25 mmHg > gastric pressure.
• Factor which maintain sphincter pressure are Anatomical, neurological and hormonal.

Anatomical factors which Minimse GOR:

• Functional anatomy of LOS
  • Internal (Circular SM) and external sphincters (in continuity with diaphragm)
  • Small portion of distal oesophagus is intra-abdominal
    • ↑ Intra-abdominal pressure → ↑ distal LOS pressure → ↑ LOS barrier pressure

Neuronal factors which minimise GOR:

• Vagal (ACh) outflow
  • Contracts the ”internal sphincter”
  • ↑ circular SM tone → ↑ LOS pressure → ↑ LOS barrier pressure
• Phrenic nerve stimulation
  • Contracts ”external sphincter” via ”pinch-cock” mechanism
  • ↑ LOS pressure → ↑ LOS barrier pressure

Hormonal Factors which limit GOR:

• ↑ LOS tone → ↑ LOS barrier pressure
  • Gastrin, CCK, motilin, α-adrenergic stimulation
• ↓ LOS tone → ↓ LOS barrier pressure
  • Secretin, VIP, GIP, glucagon, progesterone, and prostaglandins

Gladwin 2016

Answer by Gladwin