Stomach and Abomasum - Pathology

()Map ALIMENTARY SYSTEM (Map)

Introduction to the Stomach and Abomasum

• In most animals, after swallowing, food leaves the oesophagus and enters the stomach. In ruminants, food enters the abomasum after fermentation in the forestomach.
• The stomach acts as a reservoir in which a semi-solid mass (chyme) is formed from the ingested food before passing into the duodenum.
• With the exception of water, little absorption occurs in the stomach.
• Gastric juice is highly acidic, and contains:
  • HCl, produced by the parietal cells
    • Maintains gastric pH at 2, which denatures protein.
  • Pepsin, derived from pepsinogen, produced by zymogen cells
    • The action of HCl facilitates this.
• Surface epithelial cells and mucous neck cells produce mucus which forms an alkaline sheet over the epithelial surface.
  • Provides protection from the gastric juice.
• The cells of the mucosa are renewed at different rates. This is an important considerination in the pathogenesis of certain gastric diseases.
  • Surface epithelial cells and mucous neck cells are replaced about every 3 days.
  • Parietal cells and zymogen cells are produced at a slower rate; the parietal cells have a half-life of 23 days.

Defence Mechanisms

1. Secretions :
   • Mucus (inhibits contact with mucosa, protects surface).
   • Acid (parietal cells)
   • Digestive enzymes (pepsin from gastric chief cells)
2. Epithelium:
   • Provides a barrier
     • Stratified squamous epithelium; multilayered, high cell turnover
3. Movement:
   • Continuous movement discourages persistence of insult at mucosa.