[Ultrastructure of the secretory cells of the pancreatic islets in human fetuses].

An electron microscopic study of pancreatic islets of human fetuses 16--28 weeks old discovered four types of secretory cells -- B, A, D and type IV, which has not yet been given a generally accepted name. These cells contain small secretory granules more dense than granules D. In three cases endocrine elements with "mixed" granulation (D--A) were noted. The formation of insulin- and glucagon-containing granules in the ergastoplasm and Golgi complex was observed. The hormone secretion is realized by emyocitosis.