The accessory pancreatic ducts of the starling Sturnus vulgaris: an ultrastructural and light microscopic study.

Wild starlings (Sturnus vulgaris) were utilised for a study of the small accessory pancreatic ducts that pass from the pancreas to the loop of the duodenum. These ducts do not appear to have been described before in the literature. Each duct was composed of an epithelial lining of a main cell type, which had small numbers of two other cell types intermixed. A lamina propria consisting of a loose collagenous network, richly endowed with a thick nerve plexus, separated the epithelium from the muscle coat. The muscle consisted of inner longitudinal, middle transverse and outermost spiral layers. This was surrounded by a dense collagenous tunica adventitia, and the ducts were accompanied by large blood vessels. The main columnar cells of the epithelium had a strong PAS positivity, and an alcian blue-positive reaction at high molarities of magnesium chloride (greater than 0.5 M). This indicated the presence of mucopolysaccharides with a high degree of sulphation, such as heparan sulphate. Both of the staining reactions were limited to a fine apical surface reaction which probably did not extend into the cells themselves. At the electron microscope level it could be seen that the surface coat corresponded to a filamentous layer overlying short stubby microvilli on the apical surface of the epithelium. Numerous apical electron-dense inclusion granules did not appear to participate in the histochemical reaction. Comparisons of these findings with work on the main ducts of the pancreas in other species have been made and discussed.