Fine structure of acinar cells of human parotid gland

AbstractAcini of human parotid gland consist of pyramidal secretory cells and of flattened, basally placed, myoepithelial cells.Since secretory cells show a cytological organization intermediate between that of exocrine pancreas and that of mucous glands, human parotid is considered to be a seromucous gland. Short intercellular canaliculi extend between apical portions of secretory cells; more basally intercellular spaces, constantly separated from the lumen, are seen. Variations observed in cytology of secretory cells are believed to be more likely related to the presence of stages of a maturative cycle rather than to the existence of different types of cells. Secretory granules often show a bipartite structure consisting of a main portion and of a dense body (or core) contained in it. On the basis of the appearance of the main portion, dark and pale granules are recognizable. Dark granules are quite dense and homogeneous while pale granules, which tend to coalesce, are formed by a clear flocculent material. Together with granules endowed with intermediate characters, dark and pale granules are often present even in the same cell. Discharge of secretion into the lumen seems to take place following the fusion of the membrane of the secretory granule with the plasmalemma. In fact, bulging secretory granules and subluminal clefts are frequently seen. The shape of nuclei and the pattern of their chromatin content vary apparently with the cell cycle. Inside the nuclei, a distinct fibrous lamina, nucleoli and nuclear bodies are present. In addition, some nuclei exhibit a laminated inclusion arranged concentrically.Myoepithelial cells have an elongated body and thin processes extending among secretory cells. They are characterized by a filamentous cytoplasm poor in organelles.