The document discusses the four main types of endocrine cells found within the islets of Langerhans in the pancreas, including alpha, beta, delta, and F cells that produce glucagon, insulin, somatostatin, and pancreatic polypeptide, respectively. It notes that beta cells, which produce insulin, are the most numerous. The document also mentions that diabetes mellitus, characterized by insufficient insulin production or effect, is the most common pancreatic disease treated through various insulin formulations and noninsulin drugs, and that glucagon can be used to treat severe hypoglycemia.