Oesophagus

Describe the control of gastrointestinal motility, including sphincter function.

The oesophagus is a muscular tube connecting the pharynx to the stomach. The oesophagus has:

  • Skeletal muscle in its upper third
  • Smooth muscle in its lower third

Lower Oesophageal Sphincter

The LoS is:

  • The most distal 2-4cm of the oesophagus
  • Macroscopically indistinguishable from the rest of the oesophagus
    • However it has a higher concentration of nerve cells and is able to constrict at a higher pressure
  • Tonically innervated by the vagus
  • Important in the prevention of reflux
    Competency of the LoS is required to prevent reflux
    • Barrier pressure is the pressure difference between the pressure at the lower oesophageal sphincter and the pressure in the stomach, and is typically ~15-25mmHg
      Barrier pressure is affected by:
      • Changes in lower oesophageal sphincter pressure
        • Swallowing
          Barrier pressure decreases during swallowing, and transiently increases immediately afterwards.
        • Anatomical
          • Age
            Sphincter tone is decreased in neonates and the elderly.
          • Diaphgram
            An external sphincter is formed by the diaphragmatic crura, and exerts a pinch-cock action on the oesophagus.
          • Stomach
            A fold in the stomach wall just distal to the GOJ creates a flap valve, which occludes the GOJ when gastric pressure rises.
          • Oeosophagus
            The oesophagus enters the stomach at an oblique angle, limiting retrograde flow.
        • Hormonal
          • Gastrin, motilin, α-agonism increase LoS tone
          • Progesterone, glucagon, vasoactive intestinal peptide (VIP) decrease LoS tone
        • Drugs
          • ETOH, IV and volatile anaestetic agents, and anticholinergics decrease LoS tone
          • Suxamethonium, metoclopramide, and anticholinesterases increase LoS tone
      • Changes in gastric pressure
        • Raised intraabdominal pressure
          • Obesity
          • Pregnancy
      • Disease
        • Hiatus hernia
          GOJ moves into the thorax, causing:
          • Loss of pinch-cock action
          • Negative intrathoracic pressure reduces LoS pressure and therefore barrier pressure

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References

  1. Chambers D, Huang C, Matthews G. Basic Physiology for Anaesthetists. Cambridge University Press. 2015.
  2. ANZCA July/August 1999
  3. Kahrilas PJ, Pandolfino JE. Hiatus hernia. GI Motility online. 2006.
  4. ANZCA August/September 2015
Last updated 2017-10-08

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