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These folds give the stomach its well-known ability to enlarge when engorged with food. On the outermost layer of these folds you may see a thin line of material. This is mucus which helps protect the tissues below from the harsh environment of the stomach. The innermost layer is a lining of simple columnar epithelium (labeled in the high magnification image). This type of epithelium provides the greatest surface area for abosrption or secretion. In the stomach the epithelial cells exposed to the lumen are primarily constructed to resist digestion by the lumen contents. The epithelial layer forms depressions called gastric glands or pits. Within these pits are mucous secreting cells, parietal cells which secrete HCL, and chief cells which secrete pepsinogen.
If the lining of the stomach is examined with a hand lens, one can see that it is covered with numerous small holes. These are the openings of gastric pits which extend into the mucosa as straight and branched tubules, forming gastric glands. Types of Secretory Epithelial Cells.1  Mucous cells: secrete an alkaline mucus that protects the epithelium against shear stress and acid. 2  Parietal cells: secrete hydrochloric acid! 3  Chief cells: secrete pepsin, a proteolytic enzyme. 4  G cells: secrete the hormone gastrin.here are differences in the distribution of these cell types among regions of the stomach-for example, parietal cells are abundant in the glands of the body, but virtually absent in pyloric glands.