The ducts of the pancreas are lined by cuboidal cells for some of the smaller ducts and by taller, more columnar cells for some of the larger ducts. The endocrine pancreas is composed of approximately 1 million Islets of Langerhans, each approximately 100 to 200 microns in diameter. The Islets of Langerhans are approximately equally distributed throughout the substance of the exocrine pancreas. The endocrine pancreas is surrounded by a network of fine capillaries. Each endocrine islet is composed of numerous cell types of which the beta cells are the most abundant.
Beta cells secrete insulin.
Alpha cells secrete glycogen. Other relatively more minor cell populations are delta cells, PP cells, D1 and D2 cells and enterochromaffin cells. Gray H. Gray's Anatomy, 15th Edition. 916 et seq. Bloom and Fawcett a textbook of histology.