| Abstract: | The postnatal development of Brunner's glands in the opossum has been traced, using 170 specimens divided into 21 groups according to snout-rump length. The newborn opossum has a well developed small intestine, possessing villi and a differentiated intestinal epithelium with concentrations of PAS-positive material in the apical cytoplasm. The ducts of the glands begin to develop within 24 hours after birth and, as they proliferate, two cell types appear. A tall, columnar cell type lines the excretory duct whereas the intralobular duct system is lined by pyramidal cells. Intralobular ducts undergo differentiation by the 50 mm stage and, after this event, secretory units appear as outgrowths from the intralobular duct system. Development continues into early adulthood. Duodenal glands appear to evaginate simultaneously at localized foci, resulting in the formation of a duodenal sinus between glandular elements. The glands evaginate from the mucosa in the most proximal portion of the duodenum, involving both intestinal and gastric mucosal elements. That portion of mucosa lying between the forming glands is submerged and forms the floor of the duodenal sinus. Excretory duct epithelium often lines the sinus in part. The development of Brunner's glands in the opossum is completely independent both of pyloric and intestinal glands. |
