The lamina propria of the stomach is relatively scant and restricted to the limited spaces surrounding the gastric pits and glands. The stroma is composed largely of reticular fibers with associated fibroblasts and smooth muscle cells. Other components include cells of the immune system, namely, lymphocytes, plasma cells, macrophages, and some eosinophils. When
FIGURE 17.14 • Photomicrograph of cardiac glands. This photomicrograph shows the esophagogastric junction. Note the presence of the stratified squamous epithelium of the esophagus in the upper right corner of the micrograph. The cardiac glands are tubular, somewhat tortuous, and occasionally branched. They are composed mainly of mucus-secreting cells similar in appearance to the cells of the esophageal glands. Mucous secretion reaches the lumen of the gastric pit via a short duct segment containing columnar cells. 240.
inflammation occurs, as is often the case, neutrophils may also be prominent. Occasional lymphatic nodules are also present, usually intruding partially into the muscularis mucosae.
The muscularis mucosae is composed of two relatively thin layers, usually arranged as an inner circular and outer longitudinal layer. In some regions, a third layer may be present; its orientation tends to be in a circular pattern. Thin strands of smooth muscle cells extend toward the surface in the lamina propria from the inner layer of the muscularis mucosae. These smooth muscle cells in the lamina propria are thought to help outflow of the gastric gland secretions.
The submucosa is composed of a dense connective tissue containing variable amounts of adipose tissue and blood vessels, as well as the nerve fibers and ganglion cells that compose the submucosal (Meissner’s) plexus. The latter innervates the vessels of the submucosa and the smooth muscle of the muscularis mucosae.
FIGURE 17.15 • Photomicrograph of pyloric glands. This photomicrograph shows a section of the wall of the pylorus. The pyloric glands are relatively straight for most of their length but are slightly coiled near the muscularis mucosae. The lumen is relatively wide, and the secretory cells are similar in appearance to the surface mucous cells, suggesting a relatively viscous secretion. They are restricted to the mucosa and empty into the gastric pits. The boundary between the pits and glands is, however, hard to ascertain in routine H&E preparations. 120.
The muscularis externa of the stomach is traditionally described as consisting of an outer longitudinal layer, a middle circular layer, and an inner oblique layer. This description is somewhat misleading, as distinct layers may be difficult to discern. As with other hollow, spheroidal organs (e.g., gallbladder, urinary bladder, and uterus), the smooth muscle of the muscularis externa of the stomach is somewhat more randomly oriented than the term layer implies. Moreover, the longitudinal layer is absent from much of the anterior and posterior stomach surfaces, and the circular layer is poorly developed in the periesophageal region. The arrangement of the muscle layers is functionally important, as it relates to its role in mixing chyme during the digestive process as well as to its ability to force the partially digested contents into the small intestine. Groups of ganglion cells and bundles of unmyelinated nerve fibers are present between the muscle layers. Collectively, they represent the myenteric (Auerbach’s) plexus, which provides innervation of the muscle layers.