Which of the following statement(s) regarding gastric mucosal defense is/are correct?

a. Gastric mucus, produced by the surface epithelial cells, forms an unstirred layer over the gastric surface

c. Production of gastric bicarbonate is stimulated by prostaglandins and inhibited by non-steroidal antiinflammatory drugs (NSAIDs) 

Gastric mucus is produced by the surface epithelial cell. In addition to serving as a lubricant, mucus also enhances mucosal defense by forming an unstirred layer overlying the epithelial surface. In humans, the thickness of this gel layer has been reported to be about 500 µm. The vacuoles containing mucus in the cytosol of the surface epithelial cell are released by cholinergic stimulation and prostaglandins. Synthesis and release are inhibited by aspirin-like compounds that inhibit cyclooxygenase. Gel mucus retards proton mobility by a factor of only three or four, a degree that is inadequate to maintain a near neutral pH at the apical membrane of the surface epithelial cell.

In addition to producing mucus, the gastric surface epithelial cells secrete a bicarbonate-rich fluid. The amount of bicarbonate secreted is about 5% to 10% of the amount of acid that the same surface of mucosa can produce. As with mucus, bicarbonate secretion is stimulated by cholinergic agents and prostaglandins and inhibited by cyclooxygenase inhibitors.

The release of bicarbonate into the gel mucus provides a significant mucosal defense by maintaining a near neutral acidbase milieu at the apical membrane of the surface epithelial cells. When the luminal pH is around 3.0, the apical membrane of the surface epithelial cell may be exposed to a pH of about 5.0.