Question 1

How does Helicobacter pylori survive in the acidic stomach environment?

Accepted Answer

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.

Question 2

What role do bacterial virulence factors play in H. pylori-induced ulcer formation?

Accepted Answer

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.

Question 3

How do NSAIDs cause peptic ulcer disease?

Accepted Answer

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.

Question 4

How does H. pylori evade the immune system to cause chronic infection?

Accepted Answer

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.

Question 5

What structural changes occur in the gastric mucosa during peptic ulcer formation?

Accepted Answer

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.

Question 6

How does H. pylori penetrate the gastric mucus layer?

Accepted Answer

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.

Question 7

What is the relationship between prostaglandins and gastric mucosal protection?

Accepted Answer

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.

消化性溃疡病 II: 病理生理学

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