Chapter 8, Page 3  

THE STOMACH: EMBRYOLOGY, NORMAL ANATOMY, AND TUMOR DERIVATION NORMAL ANATOMY Microscopic Anatomy The normal gastric wall has the same layers as does the rest of the gut: a mucosa composed of epithelium and lamina propria with muscularis mucosae at the base, submucosa, muscularis propria, and subserosa. The Epithelium. The normal stomach has several different types of mucosa, which imperfectly correlate with the gross anatomic divisions: cardiac; body, corpus, or fundic; and antral or pyloric (figs. 8-3, 8-4, 8-5, 8-6). All mucosae have two components or compartments, the superficial pit or foveolar compartment and the deep glandular compartment. The pit compartment contains the surface epithelium that extends into the pits, which are really conduits to the lumen for glandular secretions. The surface and pit epithelia are tall columnar, with apical mucus vacuoles. These appear pale pink when stained with hematoxylin and eosin (H&E), dark red with the periodic acid-Schiff stain, and do not stain with any of the acid mucin stains, such as mucicarmine and Alcian blue (fig. 8-3). These staining characteristics indicate that these cells contain only neutral mucins. While the cells of the superficial compartment are the same throughout the gastric mucosa, the depth of the pits varies, so that in the body mucosa, the pits are short and take up about one fourth of the total mucosal thickness, while in the cardia and in the antrum, the pits are about half the total mucosal thickness. In contrast to the superficial compartment, the deep or glandular compartment differs in different parts of the stomach, not only in thickness, but also in cell type. In the cardia and in the antrum, the glands are arranged in clusters, separated by fine collagenous and smooth muscle septa. The glands contain cells that produce only neutral mucins, much like the cells of the superficial compartment (fig. 8-7). In routine preparations, their cytoplasm appears more granular than the cytoplasm of the superficial cells. In contrast, in the body and fundus, the glands contain highly specialized cells which produce acid (the parietal cells) and enzymes (the chief cells) (fig. 8-8). In H&E stained sections the parietal cells are plump, oval to round, with pale pink and slightly granular cytoplasm, while the columnar cells with darker cytoplasm are the chief or enzyme-producing cells. The parietal cells usually are more prominent in the upper part of the glandular compartment, while the chief cells are concentrated at the base. In the body mucosa, there are alternating areas of concentrated glands and shorter pits, separated by depressions in which the glandular compartment is thinner and the pits longer, the areae gastricae which can be seen grossly. The gastric mucosae contain endocrine cells, but they differ with the mucosal type (1). In the antral mucosa, the predominant endocrine cell is the gastrin-producing cell or G cell. These are located mostly in the neck and upper gland areas. In the body mucosa, G cells are rare, while the histamine-producing enterochromaffin-like (ECL) cells are more common. These are located in the lower third of the mucosa, near the chief cells. All the endocrine cells are seen better with special staining techniques, especially specific immunocytochemistry, than with the H&E stain. However, G cells can often be recognized as pear-shaped cells with finely granular cytoplasm, situated next to the basement membrane of the antral necks and glands fig. 8-9). At the junction of two different mucosal types, especially antral and body, there are transitional zones which share features of both mucosae. This transitional mucosa usually has the structure of antral mucosa, with clustered glands and tall pits; the glands usually contain mucous cells and gastrin-producing cells of antral mucosa mixed with parietal and chief cells of body mucosa. As people age, transitional mucosa seems to gradually creep proximally, especially along the lesser curvature (4). In one study of stomachs of patients with duodenal and gastric ulcers, the size of the transitional mucosa correlated with maximal acid output and the parietal cell density in the body mucosa (9). Between the pits and the glands in all mucosal types is the neck region, the generative zone for all cells of the gastric glands and pits (fig. 8-9). The cells of this narrow zone are tall, with apical mucus vacuoles, the mucous neck cells. Mitotic figures are sometimes found in this zone, especially in cases of surface epithelial injury. The Lamina Propria. The lamina propria is sparse throughout the normal stomach. In the body mucosa, there is little stroma between the glands, only scant stroma between the pits and necks, and almost no inflammatory cells of any type (fig. 8-5). In the antral and cardiac mucosae, the gland clusters are separated by a few loose collagen fibers and smooth muscle cells and the pits are more widely spaced than in the body mucosa; but even in this more spacious lamina propria, there are few inflammatory cells (fig. 8-4, 8-6). Most of the cells are smooth muscle, a few macrophages, and rare lymphocytes and plasma cells. Arterioles, venules, and capillaries are present at all levels. In contrast, lymphatics are present in the basal lamina propria, but not higher; however, in severe chronic atrophic gastritis, lymphatics may be found much higher in the mucosa (6). The Muscularis Mucosae. The muscularis mucosae is a thin double layer of smooth muscle that defines the base of the mucosa and separates it from the submucosa. Muscle fibers extend from here into the base of the mucosa, especially in the most distal part of the antrum. The Submucosa. This is a loose connective tissue layer containing blood vessels, lymphatics, nerves, and ganglion cells of the submucosal (Meissner) plexus; a few adipocytes; and a variety of scattered spindle cells that are a mix of fibroblasts, smooth muscle cells, and mast cells. The Muscularis Propria. In contrast to other parts of the gut, which have a bilayer of inner circular and outer longitudinal smooth muscle in the muscularis propria, the stomach has three muscle layers: inner oblique, middle circular, and outer longitudinal. The nerves and ganglion cells of the myenteric (Auerbach) plexus are found between the outer two muscle layers. The Subserosa and Serosa. Except where it is attached to omentum, mesocolon, and ligaments, the stomach has a thin covering of subserosal collagen, the subserosa. The subserosa is covered by a single layer of flat mesothelium, the serosa proper, a part of the visceral peritoneum. Lymphoid Tissue. There is no agreement as to whether or not the normal stomach contains lymphoid follicles (2, 3, 8). Lymphoid follicles seem to be easily induced, especially by Helicobacter pylori, a bacterium that infects the gastric mucosae, mainly the antral mucosa, so commonly that its associated gastritis may be considered a normal variant in adults in certain populations as they age. Lymphoid follicles are an expected component of that gastritis (2). In our experience, substantial lymphoid aggregates do not occur in normal stomachs in the absence of this organism. Infrequent small aggregates or follicle-like collections of small lymphocytes are occasionally found at the base of otherwise normal-appearing mucosa, but it is never clear if these lymphocytes are normal or induced by H. pylori that may be present in another part of the stomach or another stimulus.