An investigation of the vascular organisation of the canine submandibular gland.

It is known that parasympathetic nerve stimulation elevates venous pressure in the dog submandibular gland, and that the venous pressure wave is transformed to that of the arterial pulse. The vascular arrangements and histological characteristics of the dog submandibular gland were therefore examined to establish which anatomical structures are responsible for the change in venous pressure during salivation induced by parasympathetic stimulation. The acinar and ductal circulations were found to be arranged in parallel and arteriovenous anastomoses were identified in both. Microsphere injection studies demonstrated the opening of arteriovenous anastomoses in actively secreting glands. Smooth muscle cells were rarely found in venous blood vessels but venous valves were abundant in both circulations. Dense connective tissue was observed to enclose the ductal system and its accompanying structures (blood vessels, lymphatic vessels and nerves); it was most abundant in the hilum and diminished aborally. The mechanism responsible for elevating venous pressure during parasympathetic salivation is thus probably related to opening of the arteriovenous anastomoses; the increase in the amount of surrounding dense connective tissue in a central direction may facilitate the preservation of the transmitted arterial pressure and pulse in the venous system.