ORGANIZATION OF THE ENDOCRINE PANCREAS - HYPOTHETICAL UNIFYING VIEW OF THE PHYLOGENETIC DIFFERENCES

The comparative morphology of the endocrine pancreas is seemingly quite divergent in the vertebrate classes of bony fish, amphibians, reptiles, birds, and mammals. However, a hypothesis based on the concept of regional differences of islets unifies this apparent diversity. Such a hypothesis has several elements: (1) the splenic portion of the pancreas has a larger concentration of islet tissue than most other parts of the pancreas; (2) islets in the splenic portions are larger and contain A, B, and D cells but only few or no PP cells; (3) islets of the duodenal portion are smaller and are principally B cells with numerous D cells and occasional A cells. In an often limited area of this portion PP cells are found in greater number than elsewhere usually as a major component of the islets. This organization may have functional significance and not be just an embryological pattern. Higher nonmammalian vertebrates are readily encompassed by this hypothesis and mammals may be included as well. These concepts may have important implications for our understanding of the mammalian pancreas. © 1979.