5 - Salivary Gland Histology

Abstract

The paired major salivary glands contain serous acini in the parotid, serous and mucous in the submandibular gland, and mucous in the sublingual gland, in which the mucous acinar cells at the beginning of the secretory cycle stain more strongly than mature mucous cells and have been previously misinterpreted as serous cells. The acinar mucin in the parotid is neutral, in the submandibular gland is neutral and acidic, and in the sublingual gland is mainly acidic. Ionic calcium shields the polyanionic charges of the molecules of secretory material and allows their condensation into secretory granules at the Golgi apparatus. The level of ionic calcium in the salivary glands is higher than in the plasma because of the sequestered ionic calcium in the secretory granules. Microscopical concretions called sialomicroliths are present in the parenchyma of all submandibular glands and a minority of parotids. They are formed intracellularly when secretory granules and other organelles are degraded in autophagosomes during periods of secretory inactivity. They may be expelled into lumina, where they may impact in small ducts and cause obstructive atrophic foci. Striated ducts in the parotid and submandibular gland modify the isotonic primary saliva to produce final saliva that is hypotonic with low levels of sodium and chloride. There are numerous small minor salivary glands in the oral cavity and they are essentially histologically similar to the sublingual gland, apart from the posterior lingual glands of von Ebner, which are serous. All types of parenchymal cells are capable of proliferation.