The fine structure of the gastric epithelium of the rainbow trout, Salmo gairdneri, Richardson

Fine structural characteristics of the columnar mucus cells lining the surface and pits of the gastric mucosa, oxyntic cells lining the glands and the gastric endocrine cells were studied. The surface mucus cells, in addition to their primary involvement in production of mucus, showed structural adaptations. Release of the mucus vesicles was achieved by exocytosis. Transition from pit gland cells was abrupt since no mucus neck cells were observed. The oxyntic cells possessed apical and basal microvillous processes, a well developed tubulovesicular system, zymogen granules and extensive RER associated with many large mitochondria. When stimulated by distension of the stomach, the apical cytoplasm was converted into a labyrinth of cytoplasmic processes, while annular lamellae, each of which showed a short peripheral linear density appeared in the basal cytoplasm. The endocrine cells showed apical modifications as microvilli, cilia and reduced glycocalyx covering. Three types were distinguished on the basis of their granular morphology.