Pathogenesis of Peptic Ulcer
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I now have comprehensive information from multiple authoritative sources. Here is a thorough synthesis:
Pathogenesis of Peptic Ulcer Disease
Peptic ulcer disease (PUD) arises when the balance between aggressive luminal forces and the mucosal defense mechanisms tilts toward injury. The classic dictum — "No acid, no ulcer" (Schwarz, 1910) — remains valid, but modern understanding places it within a much richer framework of infection, pharmacological insult, and impaired defense.
1. The Core Concept: Imbalance of Offense vs. Defense
The gastroduodenal mucosa is continuously exposed to acid and pepsin. Under normal conditions, a layered mucosal defense prevents ulceration:
| Aggressive Factors | Defensive Factors |
|---|---|
| Hydrochloric acid | Surface mucus layer |
| Pepsin | Bicarbonate secretion |
| H. pylori | Prostaglandin-mediated mucosal integrity |
| NSAIDs | Mucosal blood flow |
| Bile salts | Epithelial restitution |
Ulceration occurs when aggressive factors overwhelm this defense — most often through H. pylori infection (~75% of cases) or NSAID use (nearly all remaining cases).
— Mulholland and Greenfield's Surgery, Scientific Principles and Practice, 7e; Robbins & Kumar Basic Pathology
2. Helicobacter pylori — The Primary Cause
Colonization and Survival
H. pylori is a spiral-shaped, flagellated gram-negative bacterium — the only human pathogen capable of persistently infecting the acidic gastric environment. It survives by:
- Orienting along a pH gradient, moving from the acidic lumen toward the epithelial surface
- Secreting urease, which hydrolyzes urea to produce ammonia, neutralizing local acid
- Expressing over 30 outer membrane adhesins to attach to gastric epithelial cells, especially at intercellular junctions
Virulence Factors
VacA (Vacuolating Cytotoxin A)
- A pore-forming cytotoxin that inserts into the host cell membrane, forming a ring/flower-shaped pore
- Allows leakage of ions, urea, and small molecules — providing nutrients to the organism
- Also inserts into endosomal and mitochondrial membranes, causing cellular swelling and damage
CagA (Cytotoxin-Associated Gene A)
- Encoded on a pathogenicity island (cag-PAI), a segment of inserted foreign DNA
- Injected directly into host epithelial cells via a bacterial type IV secretion system (molecular "needle")
- Once inside the cell, CagA is phosphorylated by host tyrosine kinases, activating signaling pathways that:
- Disrupt cytoskeletal architecture and cell polarity
- Break down apical junctions between epithelial cells → epithelial barrier disruption
- Activate a strong inflammatory response
- Disturb normal epithelial proliferation and differentiation
— Mulholland and Greenfield's Surgery, 7e, p. 2252
How H. pylori Causes Ulcers
Three patterns of gastritis determine clinical outcome:
- Pangastritis (most common): Mild–moderate inflammation of all gastric regions; acid secretion is near-normal; usually asymptomatic — no ulcers.
- Antral-predominant gastritis (~15% of infected individuals): Intense antral inflammation → loss of somatostatin-secreting D cells → unregulated gastrin release → hypergastrinemia → increased parietal cell mass and acid output → duodenal and prepyloric ulcers. This is the classic ulcer-producing pattern.
- Corpus-predominant gastritis (~1%): Leads to gastric atrophy, hypochlorhydria, and intestinal metaplasia — a precursor to gastric adenocarcinoma rather than ulcers.
Key mechanisms in ulcerogenesis:
- H. pylori-induced cytokines (IL-8, TNF-α, IFN-γ) from mucosal inflammatory cells stimulate further gastrin release from G cells
- Eradication of H. pylori normalizes basal acid output within 4 weeks and peak acid output within 6 months
- Duodenal gastric metaplasia: Acid overload causes the duodenal epithelium to undergo gastric metaplasia → H. pylori (which binds only gastric-type epithelium) colonizes the duodenum → active chronic duodenitis → duodenal ulcer
Impaired mucosal defense:
- Reduced duodenal bicarbonate secretion (↓40% vs. normal in duodenal ulcer patients)
- Decreased mucosal prostaglandin E₂ production
- Increased epithelial cell apoptosis
- Disrupted epithelial barrier permeability (via CagA)
- All normalize after H. pylori eradication
— Mulholland and Greenfield's Surgery, 7e, pp. 2250–2256; Yamada's Textbook of Gastroenterology, 7e
3. NSAIDs — The Second Major Cause
NSAIDs cause ulceration primarily through systemic suppression of prostaglandin synthesis (inhibition of COX-1 and COX-2):
- Prostaglandins normally stimulate mucus and bicarbonate secretion, maintain mucosal blood flow, and promote epithelial restitution after injury
- COX-1 inhibition → ↓ prostaglandin E₂ and I₂ → loss of all cytoprotective effects → mucosal vulnerability
- NSAIDs also cause direct topical injury in the stomach (being weak acids, they enter gastric cells in their non-ionized form and trap acid within the cell)
- NSAID-associated ulcers occur with equal frequency in the stomach and duodenum, though acute erosions are more common in the stomach
Risk amplifiers:
- Age > 65 (eightfold increased risk of bleeding vs. threefold in younger patients)
- Concomitant H. pylori infection (the two are independent and synergistic risk factors)
- Concurrent corticosteroid use (suppresses prostaglandin synthesis, impairs healing)
- Cigarette smoking (reduces mucosal blood flow and healing)
COX-2 selective inhibitors were developed to reduce GI toxicity but lose this advantage when combined with aspirin.
— Mulholland and Greenfield's Surgery, 7e, pp. 2256–2257
4. Hyperacidity States
Even without H. pylori or NSAIDs, excessive acid alone can cause ulcers:
- Zollinger-Ellison Syndrome: Gastrin-secreting tumors (gastrinomas) cause constitutive, massive acid hypersecretion → multiple ulcers in stomach, duodenum, and even jejunum
- Hypercalcemia (hyperparathyroidism, chronic renal failure): Calcium stimulates gastrin production → secondary acid hypersecretion
- Systemic mastocytosis: Histamine from mast cells directly stimulates parietal cells
— Robbins & Kumar Basic Pathology
5. Other Contributing Factors
| Factor | Mechanism |
|---|---|
| Cigarette smoking | Reduces mucosal blood flow; delays healing |
| Corticosteroids (high-dose) | Suppress prostaglandin synthesis |
| Alcohol-related cirrhosis | Associated with impaired mucosal defense |
| Chronic renal failure | Hypercalcemia → hypergastrinemia |
| COPD | Mechanism incompletely understood |
| Psychological stress | Minor role in functional dyspepsia; limited in PUD |
| Stress ulcers (ICU) | Major trauma, sepsis, respiratory failure → ischemia of mucosa |
6. Sites of Ulceration
PUD occurs wherever mucosa is exposed to acid-peptic juice:
- Duodenum (first portion / bulb) — most common
- Gastric antrum — second most common
- Esophagus — in GERD or Barrett's esophagus
- Jejunum — in Zollinger-Ellison syndrome
- Meckel's diverticulum — if it contains ectopic gastric mucosa
Summary
| Cause | Proportion | Primary Mechanism |
|---|---|---|
| H. pylori | ~75% | Inflammation → ↑ acid + ↓ mucosal defense |
| NSAIDs | ~20–25% | ↓ Prostaglandins → mucosal vulnerability |
| Acid hypersecretion (ZES, etc.) | <5% | Overwhelming acid load |
The pathogenesis of PUD is best understood as a multifactorial disruption in which gastric infection, pharmacological agents, and acid hypersecretion individually or synergistically overwhelm the mucosal defense system — ultimately leading to a breach of the epithelial barrier by acid and pepsin.
Sources: Mulholland and Greenfield's Surgery, Scientific Principles and Practice, 7e | Robbins & Kumar Basic Pathology | Yamada's Textbook of Gastroenterology, 7e | Sleisenger and Fordtran's Gastrointestinal and Liver Disease
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