A 52-year-old man with a 10-year history of peptic ulcer disease is being counseled about the pathophysiology of his condition. Which of the following is NOT a recognized mechanism of mucosal injury in peptic ulcer disease?

Explanation

## Pathophysiology of Peptic Ulcer Disease ### Mechanisms of Mucosal Injury **Key Point:** Peptic ulcer disease results from an imbalance between aggressive factors (acid, pepsin) and defensive factors (mucus, bicarbonate, blood flow, prostaglandins). ### Aggressive Factors (Cause Injury) 1. **Increased gastric acid secretion** — parietal cells produce HCl; elevated in Zollinger-Ellison syndrome and H. pylori infection 2. **Pepsin activation** — requires acidic pH; degrades mucosal proteins 3. **H. pylori colonization** — causes chronic inflammation and increased acid secretion ### Defensive Factors (Protect Mucosa) 1. **Mucus layer** — physical barrier; secreted by mucous neck cells 2. **Bicarbonate secretion** — by surface epithelial and mucous cells; neutralizes acid at mucosal surface 3. **Mucosal blood flow** — delivers oxygen, nutrients, and growth factors; maintains tissue integrity 4. **Prostaglandins (PGE₂, PGI₂)** — enhance mucus and bicarbonate secretion; maintain blood flow 5. **Epithelial cell proliferation** — rapid turnover (3–5 days) allows repair ### Why Option 3 Is Wrong **High-Yield:** Increased mucus production is a **protective response**, not an injurious mechanism. In peptic ulcer disease, the problem is *reduced* mucus quality and *impaired* bicarbonate secretion, not excessive mucus. The mucus layer becomes thin and ineffective in the presence of H. pylori or NSAIDs. ### Correct Mechanisms of Injury | Mechanism | Effect | Clinical Example | |-----------|--------|------------------| | ↑ Acid secretion | Direct mucosal damage | H. pylori, ZES | | ↓ Bicarbonate secretion | Loss of pH gradient | H. pylori, NSAIDs | | ↓ Mucus quality | Reduced barrier function | H. pylori, NSAIDs | | ↓ Blood flow | Impaired healing, ischemia | NSAIDs, stress | | ↓ Prostaglandins | ↓ Mucus, ↓ bicarbonate, ↓ blood flow | NSAIDs | **Clinical Pearl:** NSAIDs cause ulcers by inhibiting COX-1 and COX-2, which reduces prostaglandin synthesis. This leads to *decreased* mucus and bicarbonate secretion — the opposite of what option 3 describes. **Warning:** Do not confuse the body's *attempt* to protect itself (increased mucus secretion) with the actual pathophysiology. In peptic ulcer disease, protective mechanisms are overwhelmed or impaired, not enhanced.