A Study on the Diverticular Enlargement of the Rat's Submandibular Duct (II)

The occurrence of the submandibular duct reservoir was reported by Butcher (1972). Its form and functional volume (Schneyer, 1975) and the development of the submandibular complex (Kim, 1975) were studied. The shape of the cells in the epithelial lining of the reservoir had not been determined as yet. So via the techniques of histology and histochemical enzymatic activity, the epithelial lining and the function of the reservoir were investigated. The epithelial lining of the reservoir was not uniform in all regions. The proximal portion of the reservoir was lined by pseudostratified columnar epithelium and the distal portion was lined by stratified columnar or cuboidal epithelium. Acid phosphatase activity in the epithelial lining of the reservoir was observed as well as in the acini, granular convoluted duct and striated duct of the submandibular gland proper.

A Study on the Diverticular Enlargement of the Rat's Submandibular Duct

As recently as 1972 research on the submandibular duct reservoir was reported by Butcher (1972) using Long-Evans and wristar rats. The occurrence of the submandibular duct reservoir in other species of rodents has not been determined. The author has attempted to observe the occurrence of the submandibular duct reservoir in adult albino rats of the Sprague-Dawley strain as well as in mice and rabbits and to observe the morphodifferentiation of the submandibular gland, especially the submandibular duct reservoir in the rats. The whole submandibular and sublingual ducts associated with the glands and the sublingual caruncle were carefully excised under a stereomicroscope after perfusing the animal with 10% formalin solution. The submandibular and sublingual complexes were, in toto, post-fixed in Zenker's solution for 24 hours and sectioned serially. To observe the prenatal phase of the morphogenesis of the submandibular gland, serial sections of the head and neck at daily intervals from 14 days to 20 days in utero, were all fixed using Bouin's solution. The results have shown that in the serial sections of the glandular complexes of the adult rats, a diverticular enlargement of the submandibular duct near the sulbingual caruncle existed and was connected to the ordinary narrow excretory duct distal to the diverticular enlargement of the submandibular duct. The submandibular duct reservoir followed by the short terminal excretory duct opened into the oral cavity through the sublingual caruncle. The lining epithelium of the diverticular enlargement of the submandibular duct was the pseudostratified columnar type. No sublingual duct reservoir was found in the Sprague-Dawley strain rats that were investigated. In the mouse and the rabbit there was no submandibular duct reservoir found. The anlage of the submandibular gland was first observed in the 14 day old in utero specimens. In the 17 dey old in utero specimens, an apparent submandibular duct reservoir was present and the terminal buds (anlage of acini) were well differentiated. Secretory materials were seen in the lumina of the submandibular duct and in the terminal buds. These findings indicate that the secretion of the submandibular gland cannot enter the oral cavity until at least 16 days in utero.