Comparative histophysiology of the pancreatic islets

Abstract

The embryological origin of the islet tissue from a common entodermal anlage with the exocrine pancreas has been questioned recently. The islet tissue may be of. neural crest origin, and the ancestral islet cells may have been "taste cells in the gut.". Whether the separation of exocrine and endocrine tissue in the cyclostomes is an original one or not remains an open phylogenetic key question.One or more islet hormones affect the exocrine pancreas tissue. However, the islet topography in various groups shows that intrapancreatic islet dissemination is not a general prerequisite for the normal function of the exocrine tissue.The D-cell is now generally recognized as the source of a third islet hormone. A fourth granular cell type (X-cell) may well secrete a fourth islet hormone. The significance of the amphiphil islet cells, found in various species, and of the "light" cells of the cyclostomes requires further studies.The islet function in lower vertebrates is largely unknown. So far, neither the islet cytology nor the known effects of pancreatectomy allow far-reaching conclusions. The evolution of the islet functions may be only understood when their interactions with the pituitary functions become clear. ©1973 by the American Society of Zoologists.