Structure and function of the endocrine cell types of the islets.

Abstract

Publisher Summary This chapter presents the structure and function of the endocrine cell types of the islets. The islet cells are apparently interposed between and around the network of capillaries. Three cell types in the human islet can be identified with electron microscopy based upon ultrastructural differences in their secretory granules: (1) beta granules, which are round or rectangular with a crystalline structure; (2) alpha granules, which are round with a central dense core; and (3) delta granules, which are round, less dense than alpha granules and have an amorphous appearance. Electron microscopic autoradiographic studies accomplished on beta cells maintained in vitro indicated that radioactive-labeled tyrosine and leucine are first incorporated into the endoplasmic reticulum, then into the Golgi complex, and finally into beta granules. Recent electron microscopic autoradiographic studies indicate that the translocation of pro-insulin to the Golgi complex and the subsequent transport of the newly formed beta granules from the Golgi complex are energy dependent, requiring ATP. Studies on isolated islets of diabetics may be feasible, as normal human islets have been isolated by the collagenase technique and maintained in vitro in one instance.