The microvasculature of rat salivary glands. A scanning electron microscopic study.

The blood vessels together with the parenchymal components of rat salivary glands were studied by scanning electron microscopy (SEM) after removal of stromal connective tissue by acid hydrolysis plus enzymatic digestion. The three-dimensional vascular architecture was also studied by SEM of vascular corrosion cats. Each cluster of 4-5 polymorphous acini is connected with the convoluted duct via an intercalated duct. The convoluted duct usually has a sigmoid course and drains to the intralobular striated duct (about 20 microns in diameter); this has a rather straight course before connecting with the interlobular excretory duct. Myoepithelial cells with radiating processes were observed on the stromal surface of the secretory acini. Pericytes with longitudinal and circular processes were also observed surrounding the stromal surface of capillaries. The acini and convoluted ducts are surrounded by plexuses of capillaries derived from terminal arterioles which run along the intralobular duct system. The sinusoidal capillary plexus enveloping the striated duct receives blood from capillaries surrounding the acini and convoluted ducts through portal venules. The interlobular excretory ducts are richly supplied by a subepithelial network of capillaries which receive blood directly from the interlobular artery and drain into the interlobular vein. Thus, the excretory duct circulation is separated from the intralobular circulation. No arterio-venous anastomoses were observed in the gland. However, veno-venous and arterio-arterial anastomoses were often seen along the excretory duct; such anastomoses may participate in controlling the direction of blood flow through the vascular plexus around the excretory duct. The well-developed subepithelial plexus of capillaries observed around this duct is appropriate for its known absorptive/secretory functions. The capillary network around the acini is densest in the parotid gland and sparsest in the sublingual gland. The subepithelial capillary network of the excretory ducts of the submaxillary gland is denser than those of the other two glands which had similar densities.