Pathogenesis of Peptic Ulcer

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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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