Abstract
Anatomical, histological, and ultrastructural studies of the European beaver stomach revealed several unique morphological features. The prominent attribute of its gross morphology was the cardiogastric gland (CGG), located near the oesophageal entrance. Light microscopy showed that the CGG was formed by invaginations of the mucosa into the submucosa, which contained densely packed proper gastric glands comprised primarily of parietal and chief cells. Mucous neck cells represented <0.1% of cells in the CGG gastric glands and 22–32% of cells in the proper gastric glands of the mucosa lining the stomach lumen. These data suggest that chief cells in the CGG develop from undifferentiated cells that migrate through the gastric gland neck rather than from mucous neck cells. Classical chief cell formation (i.e., arising from mucous neck cells) occurred in the mucosa lining the stomach lumen, however. The muscularis around the CGG consisted primarily of skeletal muscle tissue. The cardiac region was rudimentary while the fundus/corpus and pyloric regions were equally developed. Another unusual feature of the beaver stomach was the presence of specific mucus with a thickness up to 950 µm (in frozen, unfixed sections) that coated the mucosa. Our observations suggest that the formation of this mucus is complex and includes the secretory granule accumulation in the cytoplasm of pit cells, the granule aggregation inside cells, and the incorporation of degenerating cells into the mucus.
Highlights
There are two species of beavers: the European beaver (Castor fiber) and the Canadian beaver (Castor canadensis)
The stomach of the Canadian beaver is distinguished from that of most mammals by the presence of the cardiogastric gland (CGG), a gland-like structure located along the lesser curvature near the oesophageal entrance
The CGG was located immediately behind the oesophageal entrance along the lesser curvature of the stomach; it was visible as a dark red, globular structure with a diameter of approximately 5 cm (Figure 1A)
Summary
There are two species of beavers: the European beaver (Castor fiber) and the Canadian beaver (Castor canadensis). Both species are herbivorous and belong to a small group of mammals with diet containing a large quantity of woody plants. Beavers are the second largest rodents after capybaras. The gross morphology of the Canadian beaver stomach was first reported in 1868 [1]. The stomach of the Canadian beaver is distinguished from that of most mammals by the presence of the cardiogastric gland (CGG), a gland-like structure located along the lesser curvature near the oesophageal entrance. No publications have described the morphological features of the European beaver stomach
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