Submandibular duct salivary bladder of the rat.

This investigation is a light and electron microscopic description of the submandibular duct salivary bladder of the rat, a dilation of the distal end of the main excretory duct. The wall of the bladder consists of a mucosa with pseudostratified epithelium, a submucosal layer of connective tissue, and an underlying layer of striated muscle. The pseudostratified columnar epithelium lining the bladder is composed of three cell types: light cells, dark cells, and basal cells. The lamina propria contains bundles of collagen, attenuated fibrocytes, capillaries with fenestrated endothelia, and nerve fibers which enter the epithelial layer. The capillaries of the submucosa are not fenestrated. The morphology of the wall of this structure provides evidence that the primary fluid of the submandibular gland is modified in the bladder by transepithelial fluid and ion transport.