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.
        • Diaphragm
          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.
        • Oesophagus
          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 anaesthetic 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