The ultrastructure of the centroacinar cells within the pancreas of the starling (Sturnus vulgaris).

Tissues from the dorsal lobe of the pancreas of 8 starlings (Sturnus vulgaris) were examined electron microscopically using conventionally prepared samples. Centroacinar cells were distinguished from exocrine pancreas cells by differences in size, shape, distribution, position and zymogen granule content. The centroacinar cells closely resembled ductal cells and were separated from them only by position. Both electron-lucent and electron-dense forms of centroacinar cells were observed. Centroacinar cells show a prominent single nucleus, often displaying at least one nucleolus, surrounded by cytoplasm in which lies a spectrum of both primary and secondary lysosomes, mitochondria which appear to have some tubulovesicular cristae amongst the predominating transverse cristae, a sparse para- or supranuclear Golgi apparatus, and variable populations of ribosomes and profiles of both rough and smooth endoplasmic reticulum. Cell surface features include microvilli, 'blebs' and the occasional single cilium. Centroacinar cells are believed to be involved in electrolyte secretion although, from a study of their ultrastructure, the absence of beta cytomembranes with numerous mitochondria in their neighbourhood, would appear to contra-indicate the maintenance of an osmotic gradient between the extracellular fluid and any secretory product.