The human pancreas is located in close apposition to the duodenum. It performs both endocrine and exocrine functions, but here we discuss only its exocrine function. (The endocrine functions are discussed in Chapter 35.)
The exocrine pancreas is composed of numerous small, sac-like dilatations called acini composed of a single layer of pyramidal acinar cells (Fig. 27.9). These cells are actively involved in the production of enzymes. Their cytoplasm is filled with an elaborate system of ER and Golgi apparatus. Zymogen granules are observed in the apical region of acinar cells. A few centroacinar cells line the lumen of the acinus. In contrast to acinar cells, these cells lack an elaborate ER and Golgi apparatus. Their major function seems to be modification of the electrolyte composition of the pancreatic secretion. Because the processes involved in the secretion or uptake of ions are active, centroacinar cells have numerous mitochondria in their cytoplasm.
The acini empty their secretions into intercalated ducts, which join to form intralobular and then interlobular ducts. The interlobular ducts empty into two pancreatic ducts: a major duct, the duct of Wirsung, and a minor duct, the duct of Santorini. The duct of Santorini enters the duodenum more proximally than the duct of Wirsung, which enters the duodenum usually together with the common bile duct. A ring of smooth muscle, the sphincter of Oddi, surrounds the opening of these ducts in the duodenum. The sphincter of Oddi not only regulates the flow of bile and pancreatic juice into the duodenum but also prevents the reflux of intestinal contents into the pancreatic ducts.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.