The pancreas is an exocrine and endocrine gland.
Unlike the liver, in which the exocrine and secretory (endocrine) functions reside in the same cell, the dual functions of the pancreas are relegated to two structurally distinct components.
 The exocrine component synthesizes and secretes en zymes into the duodenum that are essential for digestion in the intestine.  The endocrine component synthesizes and secretes the hormones insulin and glucagon into the blood. These hormones regulate glucose, lipid, and protein metabolism in the body.
The exocrine pancreas is found throughout the organ; within the exocrine pancreas, distinct cell masses called islets of Langerhans are dispersed and constitute the endocrine pancreas.
The exocrine pancreas is a serous gland.
The exocrine pancreas closely resembles the parotid gland, with which it can be confused. The secretory units are acinar or tubuloacinar in shape and are formed by a simple epithelium of pyramidal serous cells (Fig. 18.20a and Plate 68, page 662). The cells have a narrow free (luminal) surface and a broad basal surface. Periacinar connective tissue is minimal.
The serous secretory cells of the acinus produce the digestive enzyme precursors secreted by the pancreas. Pancreatic acini are unique among glandular acini; the initial duct that leads from the acinus, the intercalated duct, actually begins within the acinus (Fig. 18.20b; Fig. 18.21). The duct cells located inside the acinus are referred to as centroacinar cells.
The acinar cells are characterized by distinct basophilia in the basal cytoplasm and by acidophilic zymogen granules in the apical cytoplasm (see Figs. 18.20a and 18.21). Zymogen granules are most numerous in the pancreas of fasting individuals. The squamous centroacinar cells lack both ergastoplasm and secretory granules (see Fig. 18.21); thus, they stain very lightly with eosin. This weak staining helps identify them in routine histologic sections.
Zymogen granules contain a variety of digestive enzymes in an inactive form.
Pancreatic enzymes can digest most food substances. The inactive enzymes, or proenzymes, contained in pancreatic zymogen granules are listed here along with the specific substances they digest when activated.  Proteolytic endopeptidases (trypsinogen, chy carboxypeptidase, proaminopeptidase) digest proteins by by cleaving amino acids from the carboxyl or amino end of the peptide.
chapter 18 Digestive System III: Liver, Gallbladder, and Pancreas PANCR EAS 647
FIGURE 18.20 • Pancreatic acinus and its duct system. a. In this photomicrograph of a thin, H&E–stained plastic section, an intercalated duct can be seen beginning within a pancreatic acinus. The cells forming the duct within the acinus are the centroacinar cells. The eosinophilic zymogen granules are clearly seen in the apical cytoplasm of the parenchymal cells. 860. b. In this schematic diagram, observe the beginning of the intercalated duct. Note the location and shapes of the centroacinar cells within the acinus. They represent the initial lining of the intercalated duct, which drains into an intralobular collecting duct.
 Amylolytic enzymes (-amylase) digest carbohydrates by cleaving the glycosidic linkages of glucose polymers. Lipases digest lipids by cleaving ester bonds of triglycerides, producing free fatty acids. Nucleolytic enzymes (deoxyribonuclease and ribonuclease) digest nucleic acids, producing mononucleotides.