Gastrointestinal protection — What is present in the stomach to prevent self-digestion of the gastric mucosa?

Introduction:
The stomach produces potent acid and proteases to digest food, yet the organ itself normally avoids autodigestion. This question targets the protective mechanisms that shield the gastric epithelium from its own secretions.

Given Data / Assumptions:

• Gastric juice contains hydrochloric acid and pepsin.
• Gastric epithelium is exposed to mechanical and chemical stress.
• Physiological defenses exist to preserve mucosal integrity.

Concept / Approach:
The primary barrier is a thick mucus–bicarbonate layer secreted by surface mucous cells. Mucus forms a gel that traps bicarbonate, maintaining a near-neutral pH at the cell surface and preventing acid and pepsin from diffusing to epithelial membranes. Tight junctions and rapid epithelial turnover offer additional protection, while adequate mucosal blood flow supports healing and bicarbonate delivery.

Step-by-Step Solution:

Verification / Alternative check:
Clinical observations show that NSAIDs, H. pylori infection, or severe stress that compromise mucus/bicarbonate production or tight junctions predispose to gastritis and peptic ulcers, underscoring the protective role of the mucus barrier.

Why Other Options Are Wrong:

• Acid: it contributes to digestion and would increase damage if unopposed.
• Enzymes: pepsin digests proteins; it is harmful to unprotected mucosa.
• Hormones: regulate secretion and motility but do not provide a physical barrier.
• Bile salts: produced by the liver/gallbladder; their reflux can harm the gastric lining.

Common Pitfalls:
Assuming regulation alone is sufficient. Physical barrier plus bicarbonate buffering and epithelial defenses are key to preventing self-digestion.

Final Answer:
Mucus.