Stomach Self-Protection: How Cells Prevent Acid Damage

The stomach lumen contains concentrated HCl (pH 1.5–3.5) and pepsin—yet the mucosa remains intact. Multiple overlapping cellular mechanisms provide this protection:

1. Mucus-Bicarbonate Barrier

• Surface Mucous Cells: Secrete high-molecular-weight mucus gel (MUC5AC) → physical barrier.
• Mucous Neck Cells: Secrete additional mucus.
• Surface Epithelial Cells: Actively secrete HCO₃⁻ trapped in mucus → creates pH gradient (lumen pH 1–2 → epithelial surface pH 6–7).

2. Tight Junctions

Apical junctional complexes (zonula occludens) seal intercellular spaces, preventing H⁺ back-diffusion.

3. Rapid Epithelial Restitution & Renewal

• Surface cells live 3–7 days; migrate from isthmus/neck of glands.
• Restitution: adjacent cells spread over micro-erosions within minutes (trefoil factors, EGF).
• Proliferation: stem cells in isthmus divide to replace lost cells.

4. Prostaglandins (PGE₂, PGI₂)

Stromal and epithelial cells produce PGs → stimulate mucus/HCO₃⁻ secretion, maintain mucosal blood flow, inhibit acid secretion. NSAIDs inhibit COX → reduce PGs → ulcer risk.

5. Mucosal Blood Flow

Rich capillary network delivers O₂/nutrients, removes H⁺, supports rapid turnover.

6. Growth Factors

EGF, TGF-α, FGF, HGF from saliva, Brunner's glands, macrophages → promote healing.

7. Innate Immune Defense

Macrophages, neutrophils, antimicrobial peptides (defensins) combat H. pylori and other pathogens.

Disruption of any layer (NSAIDs, H. pylori, stress, alcohol, ischemia) can cause gastritis or ulcers.