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Peptic Ulcer Disease II: Pathophysiology
Peptic ulcer disease develops when protective mechanisms of the gastrointestinal mucosa are overwhelmed by harmful factors, leading to localized erosi…
H. pylori, the major cause of peptic ulcer disease, PUD, survives the stomach's acidic environment by producing urease.
Urease hydrolyzes urea into ammonia, locally neutralizing gastric acid and creating a protective microenvironment.
The bacterium then uses its flagella and mucolytic enzymes to penetrate the mucus layer and adhere to gastric epithelial cells via outer membrane proteins.
Additionally, it injects virulence factors like CagA through a type IV secretion system, disrupting cellular signaling. Meanwhile, VacA damages mitochondria, causes cell death, and suppresses T-cell responses to aid immune evasion.
H. pylori survives long-term by evading the immune system and keeping inflammation active, which gradually damages the stomach lining.
NSAID-induced PUD inhibits cyclooxygenase-1 enzymes, reducing prostaglandins essential for mucus and bicarbonate secretion and mucosal repair.
This impairs gastric defenses, allowing acid and pepsin to erode the mucosa, leading to ulcer formation.
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Q1: How does Helicobacter pylori survive in the acidic stomach environment?
H. pylori produces the enzyme urease, which hydrolyzes urea into ammonia and carbon dioxide. This creates a localized alkaline microenvironment around the bacterium, neutralizing gastric acid and allowing it to survive. The ammonia also reduces mucus viscosity, enhancing the bacterium's motility toward the epithelial surface.
Q2: What role do bacterial virulence factors play in H. pylori-induced ulcer formation?
H. pylori injects cytotoxin gene-associated protein A (CagA) through a type IV secretion system, disrupting cellular signaling and cell junctions. Vacuolating toxin A (VacA) forms membrane pores, damages mitochondria, induces apoptosis, and suppresses T-cell responses. These virulence factors collectively damage the gastric epithelium and promote immune evasion.
Q3: How do NSAIDs cause peptic ulcer disease?
NSAIDs inhibit cyclooxygenase-1 (COX-1) enzymes, reducing prostaglandin synthesis. Prostaglandins are essential for mucus secretion, bicarbonate secretion, blood flow, and mucosal repair. Without adequate prostaglandins, gastric defenses weaken, exposing the mucosa to acid and pepsin, which erode the tissue and cause ulcer formation.
Q4: How does H. pylori evade the immune system to cause chronic infection?
H. pylori alters its surface proteins to avoid recognition by toll-like receptors and induces regulatory T cells, which suppress inflammatory T-helper cell responses. This immune evasion allows persistent infection and chronic inflammation, gradually damaging the stomach lining and leading to ulcer development.
Q5: What structural changes occur in the gastric mucosa during peptic ulcer formation?
Both H. pylori infection and NSAID use impair mucosal defense, leading to chronic inflammation, epithelial damage, and necrosis. Ulcers appear as well-defined lesions extending into the submucosa. In severe cases, ulcers penetrate deeper layers, potentially causing perforation and peritonitis, which can lead to clinical manifestations and complications.
Q6: How does H. pylori penetrate the gastric mucus layer?
H. pylori uses its spiral, corkscrew shape and flagella to penetrate the gastric mucus layer. Once through the mucus, it employs mucolytic enzymes to further break down the protective barrier. The bacterium then adheres to gastric epithelial cells using outer membrane proteins, establishing infection.
Q7: What is the relationship between prostaglandins and gastric mucosal protection?
Prostaglandins are critical for maintaining gastric mucosal defense by promoting mucus secretion, bicarbonate secretion, and blood flow to the mucosa. They also support cellular repair mechanisms. When prostaglandin synthesis is inhibited by NSAIDs, these protective functions fail, leaving the mucosa vulnerable to acid and pepsin damage.