Gastric Mucosa: Structure, Protective Mechanisms & Functions

The gastric mucosa is the specialized inner lining of the stomach, engineered to withstand a hostile luminal environment (pH 1–3, pepsin, bile reflux, mechanical abrasion) while performing digestive and endocrine functions.

Histologic Layers (Lumen → Serosa)

• Surface epithelium: Simple columnar mucus-secreting cells (foveolar cells). Continuous sheet; tight junctions form barrier. Turnover: 3–7 days.
• Gastric pits (foveolae): Invaginations lined by surface epithelium; open into glands.
• Gastric glands (fundic/oxyntic): Contain:
  • Parietal (oxyntic) cells → HCl, intrinsic factor.
  • Chief (zymogenic) cells → pepsinogen.
  • Mucous neck cells → acidic mucus.
  • Enterochromaffin-like (ECL) cells → histamine.
  • Stem cells (isthmus) → differentiate upward (surface) and downward (gland).
• Pyloric glands (antrum): Mucus-secreting + G cells (gastrin), D cells (somatostatin).
• Lamina propria: Loose connective tissue, capillaries, lymphatics, immune cells (MALT), fibroblasts, myofibroblasts.
• Muscularis mucosae: Thin smooth muscle (inner circular, outer longitudinal) — local mucosal folding/movement.

Mucosal Defense Barriers (Prevent Autodigestion)

1. Mucus-bicarbonate layer: Surface mucous cells + neck cells secrete high-MW mucus gel; epithelial HCO₃⁻ secretion → pH gradient (lumen pH 1–2 → epithelial surface pH ~7).
2. Tight junctions + hydrophobic phospholipid monolayer: Paracellular barrier to H⁺ back-diffusion.
3. Rapid epithelial restitution: Migration of adjacent cells over defects (minutes–hours); proliferation from isthmal stem cells (days).
4. Rich mucosal blood flow: Delivers O₂, nutrients, HCO₃⁻; removes H⁺; "mucosal firewall."
5. Prostaglandins (PGE₂, PGI₂): Stimulate mucus/HCO₃⁻, maintain blood flow, inhibit acid. NSAIDs inhibit → ulcer risk.
6. Growth factors (EGF, TGF-α, bFGF, trefoil peptides): Promote healing.

Functions

• Acid/pepsin secretion → protein denaturation, pepsin activation.
• Intrinsic factor → B₁₂ absorption (terminal ileum).
• Gastrin, ghrelin, somatostatin → endocrine regulation of appetite, acid, motility.
• Limited absorption: alcohol, aspirin, water (minor).
• Antimicrobial: Acid kills most ingested pathogens.

Clinical Relevance

Gastritis, peptic ulcer, gastric cancer, Menetrier's disease, H. pylori infection all involve mucosal disruption. Endoscopy + biopsy assesses architecture, inflammation, metaplasia, dysplasia.