THE MAIN EXCRETORY DUCT (STENSENS) OF THE HUMAN PAROTID-GLAND - A TRANSMISSION AND SCANNING ELECTRON-MICROSCOPE STUDY

The epithelial cells of the human parotid main excretory duct (Stensen ) were studied by transmission (TEM) and scanning (SERI) electron micr oscopy through a variety of procedures that allowed the visualization; of their three-dimensional microanatomy. Stensen's duct in humans is Lined, in its distal portion, with a pseudostratified epithelium with tall principal cells and smaller basal cells, while the epithelium bec omes progressively stratified cylindrically toward the oral stoma. Gob let cells are scattered among the other epithelial cells. The principa l cells exhibit, on their lateral surfaces, numerous flattened laminar folds probably involved in transporting processes. A well-developed s mooth endoplasmic reticulum intermingled with mitochondria occupies th e cellular apices. Some vesicles are recognized on the cytoplasmic sur faces of the apical and lateral plasmalemma when cytoplasmic organelle s are removed. All these features are interpreted as being involved in the process of endocytosis. In both TEM and SEM, the principal cells show a relevant number of irregular apical protrusions that may repres ent a kind of apocrine secretion. Thus, with regard to function, the h uman Stensen's duct seems to modify the composition of saliva by proce sses of resorption and secretion, the latter coming from goblet cells as well. The basal cells have a surface microanatomy completely differ ent from that of principal cells. They exhibit, in fact, only sparse m icrovillosities and smooth areas on their lateral aspect, while their stromal surface is greatly augmented by irregular thin ramified proces ses. The role of basal cells is also discussed.