Figure 167

Mucosal surface of the stomach, a. Scanning electron micrograph showing the mucosal surface of the stomach. The gastric pits contain secretory material, mostly mucus (arrows). The surface mucus has been washed away to reveal the surface mucous cells, x 1,000.

b. Higher magnification showing the apical surface of the surface mucous cells that line the stomach and gastric pits. Note the elongate polygonal shape of the cells. x3,000.

Surface mucous cells line the inner surface of the stomach and the gastric pits

The epithelium that lines the surface and the gastric pits of the stomach is simple columnar. The columnar cells are designated surface mucous cells. Each cell possesses a large, apical cup of mucinogen granules, creating a glandular sheet of cells (Fig. 16.8). The mucous cup occupies most of the volume of the cell. It typically appears empty in routine hematoxylin and eosin (H&E) sections because the mucinogen is lost in fixation and dehydration. When the mucinogen is preserved by appropriate fixation, however, the granules stain intensely with toluidine blue and with the periodic acid-Schiff (PAS) procedure. The toluidine blue staining reflects the presence of many strongly anionic groups in the glycoprotein of the mucin, among which is bicarbonate.

The nucleus and Golgi apparatus of the surface mucous cells are located below the mucous cup. The basal part of the cell contains small amounts of rough endoplasmic reticulum (rER) that may impart a light basophilia to the cytoplasm when observed in well-preserved specimens.

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 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 mucus coat.

The lining of the stomach does not function in an absorptive capacity. However, some water, salts, and lipid-soluble drugs may be absorbed; alcohol and certain drugs, e.g., aspirin, enter the lamina propria by damaging the surface epithelium.

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. 16.8). Located between the gastric pit and the gland below is a short segment

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