Fine structure of the acinar and duct cell components in the parotid and submandibular salivary glands of the rat: A TEM, SEM, and HRSEM study

Parenchymal and stromal components of the rat parotid and submandibular glands were examined by conventional and high resolution scanning electron microscopy (HRSEM). Freeze-fractured specimens were subjected to HCl and NaOH extraction procedures to better differentiate connective tissue and cellular components. In addition, the internal three-dimensional morphology of the secretory acinar cells and duct cells was revealed by maceration with a dilute osmium tetroxide solution to selectively remove some of the cytoplasmic components. SEM and HRSEM examination of the HCl-treated samples of both glands revealed a fine filamentous network immediately surrounding each acinus. Coarser bundles of collagen that linked neighboring acini were also observed. NaOH-extracted samples selectively removed the cellular components and showed more clearly the three-dimensional structure of the connective-tissue stroma. A dense-collagenous network surrounded each lobule while more internal regions consisted of a honeycomblike pattern of evacuated spaces previously occupied by secretory acini. These spaces were smoothened in appearance and often interconnected. Apically-located secretory granules and profiles of the rough endoplasmic reticulum and Golgi apparatus in perinuclear regions were encountered in the acinar and duct cells of macerated samples by HRSEM. In addition, a phenylephrine-induced experimental condition performed in some rats resulted in a significant increase in secretory granule size and density of the serous cells.