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Stomach

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Histological section of stomach mucosa stained with Hematoxylin and Eosin (H&E). Structures include columnar epithelial cells lining the surface, gastric pits and glands in the lamina propria. The image is primarily colored in shades of pink and purple, indicating cell structures and nuclei.
Figure 1: Stomach mucosa tissue under a microscope, stained pink. Visible cells and surface features.

The stomach is a muscular organ located in the upper abdomen, between the esophagus and the small intestine. It plays a crucial role in digestion. It mixes food with gastric secretions. The stomach breaks it down into smaller particles for further digestion and absorption.

Mucosa

When not distended with food rugae, or folds, allow the stomach to collapse. The epithelial lining of the stomach is composed primarily of simple columnar epithelial cells.  These cells are specialized for secretion and protection. They are arranged in closely packed glands. These glands extend into the underlying lamina propria.  Surface mucous cells and mucous neck cells secrete mucus. This mucus forms a protective layer over the gastric epithelium. It prevents damage from gastric acid and digestive enzymes.

Within the gastric mucosa, there are millions of gastric pits that extend down into the underlying gastric glands. Gastric pits are lined with surface mucous cells. They open into the stomach lumen through which gastric secretions are released.  Parietal cells secrete hydrochloric acid (HCl). They also secrete intrinsic factor. This factor is necessary for the absorption of vitamin B12 in the small intestine. Chief cells secrete pepsinogen, the inactive precursor of the proteolytic enzyme pepsin, which helps to digest proteins. Enteroendocrine cells secrete hormones such as gastrin, somatostatin, and histamine, which regulate gastric acid secretion, motility, and other digestive functions.

Submucosa

Beneath the mucosa is the submucosa, a layer of connective tissue containing blood vessels, lymphatic vessels, and nerves. The submucosa provides support and supplies nutrients to the mucosa. It serves as a conduit for blood vessels and nerves entering the stomach wall.

Muscularis Externa

The muscularis externa is a layer of smooth muscle. It is responsible for the contractions that mix and propel food through the stomach. It consists of three layers of smooth muscle fibers. These layers are an inner oblique layer, a middle circular layer, and an outer longitudinal layer.  This specialization of a third, oblique layer aids in segmentation. It supports the churning and mixing process of mechanical digestion within the stomach.

Serosa

The outermost layer of the stomach is the serosa. It is a thin, smooth, serous membrane. This membrane covers the outer surface of the stomach and helps to protect and lubricate it. In areas where the stomach is not covered by peritoneum, such as the posterior surface, it is called the adventitia. The outermost layer in these areas is called the adventitia.   

Histopathological slide of stomach mucosa, stained pink and purple. Glandular pits are seen on the left with underlying granular glands. On the right, submucosa with collagen fibers and a lymphocyte aggregate is visible. The field is evenly illuminated.
Figure 2: Stomach mucosa histology showing glandular structures and tissue layers.
Histological cross-section of stomach tissue, emphasizing the muscularis externa. Stained with hematoxylin and eosin (H&E), producing pink hues. The muscularis externa is characterized by distinct layers of smooth muscle fibres. The image showcases the cellular structure and arrangement of tissue under high magnification.
Figure 3: Microscopic view of stomach muscularis externa layer, stained pink. Tissue structure visible.
Micrograph of stomach serosa stained with hematoxylin and eosin (H&E). The stain highlights cells with pink to rose coloration. Visible structures include the mesothelium layer at the top, followed by the subserosal connective tissue with collagen fibers and fibroblasts. Capillaries are also discernable. The image displays from top to bottom.
Figure 4: Stomach serosa microscopic view. Pink-stained tissue showing cellular structures and membranes.

Functions

Mechanical Digestion via Segmentation

Chemical Digestion with low-pH Enzymes

Specializations

 The stomach is bound by two sphincters controlling entry and exit.  The cardiac sphincter separates the esophagus from the stomach. The pyloric sphincter separates the stomach from the duodenum, the upper portion of the small intestine.
The rugae or folds of the stomach allow it to expand and collapse. This function is similar to the esophageal folds. It’s also comparable to the circular folds of the small intestine.  The rugae allow the stomach to expand and hold up to about 1 quart of food.

Figures 1, 3, & 4: Stomach, H&E, 20X Slide 156
Figure 2: Esophagus and stomach, H&E, 40X Slide 155
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.

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