Species: rat (Rattus norvegicus; mammal).
Technique: paraffin embedding, stained with haematoxylin-eosin
A significative change in the anatomy and histology of the digestive tract happens as one transitions from the esophagus to the stomach (Figure 1).
As the other regions of the digestive dusct, the stomach is made up of four layers: mucosa, submucosa, muscularis, and serosa.
The mucosa is formed of a simple epithelium with columnar cells arranged in tightly packed folds. The deep parts of these folds (also known as the fundus) form the gastric glands (Figure 2), that may be simple or branched tubular glands. The secretory epithelium of these deeper parts of gastric glands releases mucous compounds that cover and protect the luminal surface of the stomach.
The stomach epithelium rests on the basal lamina. Beneath the basal lamina lies the lamina propria of the mucosa. The lamina propria is a thin layer of loose connective tissue with abundant diffuse lymphoid tissue, as well as collagen and reticular fibers. The muscularis mucosae is located under the lamina propria, which comprises two layers of muscle cells, one arranged circularly (perpendicular to the major axis of the stomach) and the other longitudinally (parallel to the major axis of the stomach). A third layer, with obliquely oriented cells, is occasionally observed.
The submucosa consists of connective tissue that contains many lymphocytes and plasma cells. Abundant blood and lymphatic vessels are also present in this layer.
The muscularis propria is found bebeath the mucosa. It consists of three layers of smooth muscle: the inner oblique layer, the middle circular layer, and the outer longitudinal layer. Between the circular and longitudinal layers, there are nerve fibers forming the Auerbach's plexus, which coordinates the contractions of the stomach during digestion.
The serosa layer of the stomach is similar to that found in other parts of the digestive tube. It is continued with the visceral and abdominal cavity walls.