The pancreas is a dual exocrine and endocrine gland. The exocrine pancreas is specialized for secretion of digestive enzymes (e.g. proteinases, lipases, amylases, and nucleases) that are carried by a duct system to the duodenum. Small areas of endocrine tissue (the islets of Langerhans) are interspersed amongst the exocrine pancreas and secrete key hormones (insulin, glucagon, and somatostatin) that control blood glucose levels.

Examine sections of pancreas (sample 1, sample 2, sample 3) with low power and observe the overall organization.

• Lobules separated by CT septa
• Adipocytes
• Pale-staining pancreatic islets of Langerhans
• Densely packed secretory acini
• Excretory ducts

Using higher magnification, examine sample 1  in more detail. Identify acini in an area where the polarized nature of the cells is apparent.

• Note that the lumens of pancreatic acini are almost too small to see with the light microscope.
• When examining the acinar cells, note the basophilic staining in the basal region due to abundant RER and the eosinophilic staining in the apical region due to abundant protein-rich secretory vesicles.
• Examine the pale staining centroacinar cells at the center of the acini leading into the intercalated ducts lined by pale staining, low cuboidal epithelium.
• Examine the ducts, recalling that the intercalated ducts lead into intralobar, interlobular, and then into the main pancreatic duct. The ductal epithelium transitions to simple columnar and eventually to stratified cuboidal-columnar epithelium in the larger excretory ducts.

Pancreatic islets (of Langerhans).