Mills Ch22 Stomach

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CHAPTER 22:  Stomach

cells, and lymphocytes. It is also normal to find occasional polymorphs and mast cells. As mentioned, the lamina pro- pria contains capillaries, arterioles, and nonmyelinated nerve fibers.A few fibers of smooth muscle may extend upward from the muscularis mucosa into the lamina propria, occasionally reaching the superficial portion of the mucosa, especially in the distal antrum. The lymphoid tissue of the stomach has not been stud- ied as extensively as that of the small bowel. The isolated lymphocytes and plasma cells in the lamina propria are predominantly of B-cell lineage and are immunoglobulin A (IgA) secreting. Intraepithelial lymphocytes are present in the stomach but are much less frequent than in the small bowel. They are commonly surrounded by a clear halo, which represents a formalin fixation artifact. These lymphocytes, as well as small numbers of lamina propria lymphocytes, are of T-cell origin. Recently it has been shown that small numbers of pri- mary lymphoid follicles (aggregates of small lymphocytes) can be found in the normal stomach (22). However, sec- ondary lymphoid follicles (follicles with germinal centers) are found only in gastritis, usually secondary to infection with H. pylori. Submucosa The submucosa is located between the muscularis mucosae and the muscularis propria and also forms the cores of the gastric rugae. It consists of loose connective tissue, in which many elastic fibers are found. The autonomic nerve plexus of Meissner is found in the submucosa, as are plexuses of veins, arteries, and lymphatics. Muscular Components In classical anatomy texts (23,24), the main muscle mass of the stomach is referred to as the muscularis externa. In North America, however, the alternative name, muscularis propria, is widely used and preferred. This is because the term muscularis externa is ambiguous, as it is sometimes not clear whether it refers to the whole of the main muscle mass or only its external layer. Three layers of fibers can be recognized in the muscula- ris propria: outer longitudinal, inner circular, and innermost oblique. The external fibers are continuous with the longi- tudinal muscle of the esophagus. The inner circular layer is aggregated into a definite sphincter mass at the pylorus, where it is sharply separated from the circular fibers of the duodenum by a connective tissue septum. The oblique muscular fibers are an incomplete layer present interior to the circular fibers and are most obvious in the cardiac area. Evidence for the presence of a circular sphincter at the cardia is controversial (25). Histologic examination is not conclusive, and although radiologic techniques show arrest of swallowed food at this level, this may be due to external compression from the adjacent crura of the diaphragm.

with regular nuclei, with an even distribution and clear cytoplasm (a fixation artifact). In pyloric mucosa, the cells are more numerous with between 20 and 50 cells per crypt (Fig. 22.12B). This wide range makes it difficult to assess mucosal biopsies for the presence of G-cell hyperplasia. Hormones from the endocrine cells either enter the blood or modulate other locally situated cells (paracrine effect). The EC cells and some of the ECL cells have argen- taffin granules, which can be stained by Fontana, Masson, or the diazo technique. Other cells are argyrophilic but not argentaffinic and may be stained by the Grimelius technique (19). Silver stains have now been replaced by more sensi- tive immunologic techniques (synaptophysin and chromo- granin) (20). Individual hormones, for example, gastrin and somatostatin, may be demonstrated by specific antibodies. In addition to the presence of hormones in epithelial cells, some hormones also are found in neurons and nerve end- ings present in the stomach wall and mucosa. It is generally believed that vasoactive intestinal peptide is predominant in neural tissue and that catecholamines, bombesin, substance P, enkephalins, and possibly gastrin are also found at these sites. When hyperplasia of G cells occurs, it is generally lin- ear. Overgrowth of ECL cells in the fundic mucosa occurs secondary to hypergastrinemia, arising as a consequence of pernicious anemia which causes destruction of parietal cells and loss of gastric acidity. ECL cell hyperplasia has been divided into five growth patterns: pseudohyperplasia, hyper- plasia, dysplasia, microinfiltration, and neoplasia (21). Lamina Propria The epithelial cells of the surface, foveolae, and glands all rest on a basement membrane, which is similar to that seen elsewhere in the intestinal tract. Within the mucosa is a well- developed lamina propria that provides structural support, consisting of a fine meshwork of reticulin with occasional col- lagen and elastic fibers that are condensed underneath the basement membrane (Fig. 22.13). The lamina propria is more abundant in the superficial portion of the mucosa between the foveolae, especially in the pyloric mucosa. It contains numerous cell types, including fibroblasts, histiocytes, plasma

FIGURE 22.13  Normal gastric oxyntic mucosa (reticulin).