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Lecture Human anatomy and physiology - Chapter 23: The digestive system (part c)

Chapter 23 part c provides knowledge of the digestive system. The main contents in this chapter include all of the following: Pancreas, pancreatic juice, regulation of bile secretion, regulation of pancreatic secretion, digestion in the small intestine, requirements for digestion and absorption in the small intestine,.and other contents. | 23 The Digestive System: Part C Pancreas Location Mostly retroperitoneal, deep to the greater curvature of the stomach Head is encircled by the duodenum; tail abuts the spleen Pancreas Endocrine function Pancreatic islets secrete insulin and glucagon Exocrine function Acini (clusters of secretory cells) secrete pancreatic juice Zymogen granules of secretory cells contain digestive enzymes Figure 23.26a Small duct Acinar cells Basement membrane Zymogen granules Rough endoplasmic reticulum (a) Pancreatic Juice Watery alkaline solution (pH 8) neutralizes chyme Electrolytes (primarily HCO3–) Enzymes Amylase, lipases, nucleases are secreted in active form but require ions or bile for optimal activity Proteases secreted in inactive form Pancreatic Juice Protease activation in duodenum Trypsinogen is activated to trypsin by brush border enzyme enteropeptidase Procarboxypeptidase and chymotrypsinogen are activated by trypsin Figure 23.27 Stomach Pancreas Epithelial cells Trypsinogen (inactive) Chymotrypsinogen (inactive) Procarboxypeptidase (inactive) Trypsin Chymotrypsin Carboxypeptidase Membrane-bound enteropeptidase Regulation of Bile Secretion Bile secretion is stimulated by Bile salts in enterohepatic circulation Secretin from intestinal cells exposed to HCl and fatty chyme Regulation of Bile Secretion Gallbladder contraction is stimulated by Cholecystokinin (CCK) from intestinal cells exposed to proteins and fat in chyme Vagal stimulation (minor stimulus) CKK also causes the hepatopancreatic sphincter to relax Regulation of Pancreatic Secretion CCK induces the secretion of enzyme-rich pancreatic juice by acini Secretin causes secretion of bicarbonate-rich pancreatic juice by duct cells Vagal stimulation also causes release of pancreatic juice (minor stimulus) Figure 23.28 Chyme enter- ing duodenum causes release of cholecystokinin (CCK) and secretin from duodenal enteroendocrine cells. CCK (red dots) and secretin (yellow dots) enter the bloodstream. CCK induces . | 23 The Digestive System: Part C Pancreas Location Mostly retroperitoneal, deep to the greater curvature of the stomach Head is encircled by the duodenum; tail abuts the spleen Pancreas Endocrine function Pancreatic islets secrete insulin and glucagon Exocrine function Acini (clusters of secretory cells) secrete pancreatic juice Zymogen granules of secretory cells contain digestive enzymes Figure 23.26a Small duct Acinar cells Basement membrane Zymogen granules Rough endoplasmic reticulum (a) Pancreatic Juice Watery alkaline solution (pH 8) neutralizes chyme Electrolytes (primarily HCO3–) Enzymes Amylase, lipases, nucleases are secreted in active form but require ions or bile for optimal activity Proteases secreted in inactive form Pancreatic Juice Protease activation in duodenum Trypsinogen is activated to trypsin by brush border enzyme enteropeptidase Procarboxypeptidase and chymotrypsinogen are activated by trypsin Figure 23.27 Stomach Pancreas Epithelial cells Trypsinogen .