Morphological architecture of the developing pancreas in quail embryos: A histological and ultrastructural perspective.

Organogenesis of the avian pancreas is a critical developmental process that ensures proper digestive and metabolic functions in birds. This study investigated the morphogenesis and ultrastructural differentiation of the quail pancreas. Fifty-eight quail embryos from day 5 to day 17 of incubation were used for this study. The developing pancreas consistently composed of exocrine and endocrine portions. On day 5, primitive pancreatic tubules (duct-like structures) appeared within the duodenal mesenchyme, lined with pseudostratified and simple columnar epithelium, and associated with early endocrine clusters representing the islets of Langerhans. By day 6, the pancreas was enclosed by a delicate capsule, and the pancreatic cells became cuboidal to pyramidal with prominent basally located nuclei. Progressive lobulation occurred from days 8 and 9, forming dorsal, ventral, third, and splenic lobes with increased vascularization and telocytes distribution. On 10th day of incubation, four distinct lobes were established, and each lobe had its own capsule on 14th day. By day 17, mature serous acini exhibited basophilic basal cytoplasm and apical zymogen granules, indicating functional secretory activity. Ultrastructurally, exocrine acinar cells displayed abundant rough endoplasmic reticulum, prominent nuclei, and diverse zymogen granules. Centroacinar and intercalated ductal cells formed the initial ductal network. Telocytes appeared in perivascular and interacinar regions, suggesting a regulatory role in tissue organization. Endocrine islets were made of α-, β-, and δ-cells, each possessing distinct secretory granules corresponding to glucagon, insulin, and somatostatin secretion, respectively. Grossly, the pancreas developed progressively between the duodenal limbs and attained distinct lobular organization by hatching. These findings elucidate the prehatching structural maturation of the quail pancreas, establishing a foundation for understanding avian pancreatic development and function.