Abstract
Human duodenal mucosa obtained in three surgical operations was examined under the electron microscope with the following results:
1. In all the three cases five different types of endocrine cells occurred in the basal parts of the crypts and of the duodenal gland ducts: 1) enterochromaffin (EC) cells with dense, polymorphous granules, 2) type 2 cells with large-sized round granules, 3) type 3 cells characterized by small round granules and an infranuclear fibrous substance, 4) type 4 cells containing similar granules and characterized by a rounded shape with a constricted neck and an apical disk provided with very long microvilli, and 5) intestinal D cells with granules morphologically identical with those in the pancreatic D cells.
2. All these types of cells seemed to face the lumen of the crypts of ducts with a narrowed apical process covered with microvilli. Discussion was made on the possible significance of this structure for the perception of some information from the lumen such as the changes in pH.
