What is not correct regarding the mucosal barrier: a) formed by basement of mucus glands, b) stimulated by prostaglandin (PG) to secrete mucus, c) Brunner's glands to deal with gastric pH, or d) protects gastric mucosa from irritative materials such as bile salts?

Gastric Mucosal Barrier: Identifying the Incorrect Statement

Option (a) is incorrect—the mucosal barrier is not formed by the basement membrane of mucus glands, but rather by the adherent mucus gel layer secreted onto the epithelial surface combined with bicarbonate secretion that creates a pH gradient.

Understanding the Gastric Mucosal Barrier Components

The gastric mucosal barrier consists of several integrated protective mechanisms:

The Adherent Mucus Gel Layer

• The primary structural component is the continuous adherent mucus gel layer that sits on top of the gastric epithelium, not a basement membrane of glands 1
• This adherent mucus creates a stable, unstirred layer that supports surface neutralization of acid and acts as a physical barrier against luminal pepsin 1
• The mucus gel layer holds a large H+ concentration gradient (10^5) from lumen to mucosa under physiological conditions 2

Bicarbonate Secretion and pH Gradient

• Bicarbonate secretion into the adherent mucus gel creates a pH gradient with near-neutral pH at the epithelial surface, despite luminal acid 1
• This bicarbonate secretion is quantitatively sufficient to maintain near-neutral pH at the mucus-mucosal surface interface 1
• The mucus bicarbonate barrier is sufficient for protection of gastric mucosa against acid and pepsin under normal physiological conditions 1

Evaluating Each Statement

Statement (b): Prostaglandin Stimulation - CORRECT

• Prostaglandins do stimulate mucus synthesis and secretion as part of their cytoprotective function 3
• Prostaglandins also stimulate mucosal bicarbonate secretion, mucosal blood flow, and cellular repair 3
• Endogenous prostaglandins likely influence mucus and bicarbonate secretion by both stomach and duodenum 4
• Inhibition of prostaglandin synthesis by NSAIDs is associated with increased gastroduodenal mucosal damage and ulceration 3

Statement (c): Brunner's Glands and Gastric pH - CORRECT

• Brunner's glands (located in the duodenum) secrete bicarbonate-rich mucus to neutralize gastric acid entering the duodenum 5
• Brunner's glands produce PG II (pepsinogen II) but not PG I, contributing to duodenal protection 5
• These glands help deal with gastric pH as it enters the duodenum, making this statement correct 5

Statement (d): Protection from Bile Salts - CORRECT

• The mucosal barrier does protect against irritative materials including bile salts 6, 2
• Bile salts are classic barrier-breaking agents that, when combined with acid, can damage the mucosa 2
• The adherent mucus gel layer provides physical protection against various luminal irritants 1

Common Pitfalls to Avoid

• Do not confuse the adherent mucus gel layer (which forms the barrier) with the basement membrane of mucus-secreting glands 1
• The barrier is a functional property at the epithelial surface, not an anatomical structure within glands 2
• While no discrete anatomical "barrier" has been described, the gel mucus and epithelial phospholipids are considered constituents of the functional barrier 2
• The barrier maintains its protective function through active bicarbonate secretion, not just passive mucus coverage 1