Ultrastructure of Brunner's glands in the horse

Investigation of the duodenal submucosal glands of Brunner in the horse for the first time at the ultrastructural level has clarified some of the unique features of these equine glands. The horse is one of the very few mammals in which Brunner's glands are comprised of both mucous and serous tubuloacinar glands. Although the ultrastructural differences between the serous and mucous cell types are marked, particularly with respect to secretory granules and rough endoplasmic reticula, these cell types closely correspond to serous and mucous cells in the upper digestive system of other mammals. A minor and distinct population of goblet cell-like mucous cells, and endocrine-like cells were also observed in equine Brunner's glands. Both the serous and mucous cells appear to empty into common ducts which enter the base of the duodenal crypts. These submicroscopic cytologic data taken together with other physiologic data would suggest that, in the horse, Brunner's glands function both to provide mucosal protection in the proximal duodenum as well as to release digestive enzymes, such as lipase or other unidentified materials.