Stomach

The stomach extends from the esophagus to the duodenum. It is separated from the small intestine by a muscular ring, the pyloric sphincter. The upper portion acts as a reservoir and has no or slight peristaltic contractions. The lower half has peristaltic contractions that increase in intensity toward the pyloric sphincter; it is in this region that most of the mixing actions occur.

This slide is from the lower part of the stomach. First examine the slide under the scanning objective and notice the folds, or rugae. 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.