The most conspicuous tissue feature of the stomach is the thick glandular mucosa, packed with gastric glands which secrete digestive enzymes and acid.
The thick mucosa of the stomach is characterized by closely packed tubular glands beneath a surface of simple columnar epithelium.
The surface is indented into numerous short gastric pits which open freely to the lumen. The entire surface consists uniformly of surface mucous cells, which protect the stomach from self-digestion.
Failure of the surface mucous cells to protect the stomach wall can lead to an ulcer. See WebPath (low mag), WebPath (high mag), or Milikowski & Berman's Color Atlas of Basic Histopathology, pp. 240-241.
Gastric glands comprise the bulk of the mucosa beneath the pits. Although lamina propria separates the individual glands, most of the mucosal volume is occupied by secretory cells, primarily parietal cells and chief cells.
The submucosa of the stomach is relatively unspecialized.
The muscularis externa of the stomach is thicker than elsewhere along the tract. The smooth muscle fibers of the muscularis may form an oblique layer in addition to the inner circular and outer longitudinal" layers that charaterize the rest of the tract. Multiple layers are often difficult to distinguish microscopically, because in any given section only one of the layers (at most) will be cut in cross section while the others will be more or less oblique.
As elsewhere along the tract, the serosa of the stomach is normally unremarkable.
With their tubular shape and mucous-secretory surface, gastric pits have a distinctly glandular appearance. However, since one single cell type, the surface mucous cell, is continuous over the entire stomach surface, the pits are usually regarded not as glands but just as short indentations of the surface epithelium.
Beneath the gastric pits, the mucosa of the stomach is filled with closely packed tubular glands, which differ by region (i.e., cardiac, fundic, pyloric). Histologically, most of the stomach wall contains gastric glands (or fundic glands). These consist primarily of parietal cells and chief cells. The fundic glands also contain mucous neck cells and stem cells.
Gastric parietal cells (oxyntic cells) secrete acid, by pumping chloride and hydrogen ions. These cells are unique not only in function but also in microscopic appearance. Parietal cells may be found at any level in the fundic glands, but they are most common in the middle region.
Gastric chief cells secrete the digestive enzymes and have typical serous-secretory appearance. Chief cells may be found at any level in the fundic glands, but they are most common in the lower region, toward the muscularis mucosae.
Mucous neck cells are inconspicuous cells with a typical mucous-secretory appearance. These cells are most common in the upper region of the fundic glands. Their specific function remains unclear.
Stem cells, located at the at the top of the glands where they open into the pits, are responsible for replenishing the gland cells and also the surface mucous cells that protect the stomach surface. These cells are difficult to notice and even more difficult to identify in routine histological preparations.
Microscopic appearance of fundic glands. In routine sections, the arrangement of secretory cells into tubular glands is often not readily apparent. The cells may appear to be all jumbled together, or associated into cords, for several reasons:
- The glands are not quite straight and not quite parallel to one another.
- The cells which comprise the glands vary in size, shape and appearance.
- There is often little or no free space in the glandular lumens.
Since tubular organization often cannot be clearly seen, the orientation of the secretory cells is also often obscure. Nevertheless, the predominant secretory cells (parietal cells and chief cells) may be recognized as epithelial by their typical round, euchromatic nuclei. The glandular architecture usually appears most neatly where chief cells predominate, deep in the mucosa near the mucularis mucosae.
Individual glands are separated from one another by a thin stroma of lamina propria. The lamina propria may be recognized by the densely heterochromatic, irregular or flattened nuclei of its fibroblasts and endothelial cells. This lamina propria contains the capillaries which nourish the glands and the stomach surface and which also supply the materials needed for secretion.
The junction between esophagus and stomach is marked by a sharp transition from the stratified squamous epithelium of the esophageal mucosa to the simple columnar epithelium of the gastric mucosa.
The mucosa of the stomach is divided, somewhat arbitrarily, into three regions: the cardiac stomach, the fundic stomach, and the pyloric stomach.
These anatomical regions display differ histologically primarily in the length and composition of the mucosal glands.
Cardiac glands are relatively short, relative to the fundic and pyloric glands.
Fundic glands are described above.
Pyloric glands are especially extensive. These glands are functionally and structurally similar to Brunner's glands of the duodenum. Both are tubular mucous glands which secrete alkaline mucus. They remain within the mucosa in the stomach but expand across the muscularis mucosae to fill the submucosa of the duodenum.
Both cardiac and pyloric glands are predominantly mucous (i.e., few parietal or chief cells). This makes functional sense, since mucus can help protect the adjacent regions of the tract from damage by stomach acid and digestive enzymes. Surface mucous cells protect the stomach lining, but the esophagus and duodenum lack any such protection.
The pyloric stomach is also characterized by a considerable thickening of the muscularis externa, forming the pyloric sphincter.
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Last updated: 17 May 2010 / dgk