The mucous secretion from the surface mucous cells is described as visible mucus because of its cloudy appearance. It forms a thick, viscous, gel-like coat that adheres to the epithelial surface; thus, it protects against abrasion from rougher components of the chyme. Additionally, its high bicarbonate and potassium concentration protects the epithelium from the acidic content of the gastric juice. The bicarbonate that makes the mucus alkaline is secreted by the surface cells but is prevented from mixing rapidly with the contents of the gastric lumen by its containment within the mucous coat. Finally, prostaglandins (PGE2) appear to play an important role in protecting gastric mucosa. They stimulate secretion of bicarbonates and increase thickness of the mucus layer with accompanied vasodilatation in the lamina propria. This action improves supply of nutrients to any damaged area of gastric mucosa, thus optimizing conditions for tissue repair.
The lining of the stomach does not function in an absorptive capacity. However, some water, salts, and lipid-soluble drugs may be absorbed. For instance, alcohol and certain drugs such as aspirin or nonsteroidal anti-inﬂammatory drugs (NSAIDs) enter the lamina propria by damaging the surface epithelium. Even small doses of aspirin suppress the production of protective prostaglandins by the gastric mucosa. In addition, aspirin’s direct contact with the wall of the stomach interferes with the hydrophobic properties of the gastric mucosa.
Fundic Glands of the Gastric Mucosa
The fundic glands produce the gastric juice of the  stomach.
The fundic glands, also called gastric glands, are present throughout the entire gastric mucosa except for the relatively small regions occupied by cardiac and pyloric glands. The fundic glands are simple, branched, tubular glands that extend from the bottom of the gastric pits to the muscularis mucosae (see Fig. 17.8). Located between the gastric pit and the gland below is a short segment known as the isthmus. Isthmus of the fundic gland is a site of stem cells location (stem cell niche) in which stem cells replicate and differentiate. Cells destined to become mucous surface cells migrate upward in the gastric pits to the stomach surface. Other cells migrate downward, maintaining the population of the fundic gland epithelium. Typically, several glands open into a single gastric pit. Each gland has a narrow, relatively long neck segment and a shorter and wider base or fundic segment. The base of the gland usually divides into two and sometimes three branches that become slightly coiled near the muscularis mucosae. The cells of the gastric glands produce gastric juice (about 2 L/day), which contains a variety of substances. In addition to water and electrolytes, gastric juice contains four major components:  Hydrochloric acid (HCl) in a concentration ranging from 150 to 160 mmol/L, which gives the gastric juice a low pH (1.0 to 2.0). It is produced by parietal cells and initiates digestion of dietary protein (it promotes acid hydrolysis of substrates). It also converts inactive pepsinogen into the active enzyme pepsin. Because HCl is bacteriostatic, most of the bacteria entering the stomach with the ingested food are destroyed. However, some bacteria can adapt to the low pH of the gastric contents. Helicobacter pylori contains large amounts of urease, the enzyme that hydrolyzes urea, in its cytoplasm and on its plasma membrane. This highly active enzyme creates a protective basic “ammonia cloud” around the bacterium, allowing it to survive in the acidic environment of the stomach (Folder 17.1).