The GI System 3 (2023) PDF

WEEK 14 MPharm Programme The Gastro-intestinal System 3 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 GI System The Small Intestine WEEK 14 Three Main Subdivisions Duodenum & Hepatopancreatic organs Jejunum Ileum Slide 58 of 83 MPharm PHA112...

WEEK 14 MPharm Programme The Gastro-intestinal System 3 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 GI System The Small Intestine WEEK 14 Three Main Subdivisions Duodenum & Hepatopancreatic organs Jejunum Ileum Slide 58 of 83 MPharm PHA112 GI System WEEK 14 The Duodenum & Hepatopancreatic Region Slide 59 of 83 MPharm PHA112 GI System The Duodenum WEEK 14 The first 10 inches of small intestine First site of intensive digestion Receives bile & pancreatic juice via the common bile duct & main pancreatic duct Arrival of chyme stimulates release of hepatic & pancreatic secretions fatty chyme in the duodenum  release of CCK  release of bile & pancreatic enzymes acid in chyme  release of secretin  release of pancreatic bicarbonate  neutralizes the acidity Slide 60 of 83 MPharm PHA112 GI System WEEK 14 Structure of the Pancreas Slide 61 of 83 MPharm PHA112 GI System WEEK 14 Functional Anatomy of Pancreas Exocrine Duct cells secrete aqueous bicarbonate solution Acinar cells secrete pancreatic juice – proteases, amylase, lipase Endocrine Islets of Langerhans -cells – secrete insulin -cells – secrete glucagon Slide 62 of 83 MPharm PHA112 GI System WEEK 14 Secretions of the Pancreas Slide 63 of 83 MPharm PHA112 GI System WEEK 14 Hormonal Control of Pancreatic Exocrine Secretion Slide 64 of 83 MPharm PHA112 GI System WEEK 14 Activation of Pancreatic Enzymes Slide 65 of 83 MPharm PHA112 GI System WEEK 14 The Liver & Hepatic Portal Circulation Slide 66 of 83 MPharm PHA112 GI System The Liver WEEK 14 The largest gland in the body Composed of ‘plates’ of liver cells (hepatocytes) main digestive function is the production of bile Bile a fat emulsifier a yellow-green, alkaline solution contains bile salts, bile pigments, cholesterol, neutral fats, phospholipids & electrolytes stored & released from gallbladder Slide 67 of 83 MPharm PHA112 GI System WEEK 14 Fat Emulsification by Bile Salts Slide 68 of 83 MPharm PHA112 GI System WEEK 14 Slide 69 of 83 Control of Bile Release MPharm PHA112 GI System WEEK 14 Enterohepatic Circulation of Bile Salts Slide 70 of 83 MPharm PHA112 GI System WEEK 14 Digestion & Absorption in the Small Intestine Slide 71 of 83 MPharm PHA112 GI System WEEK Absorption in Small Intestine 14 Duodenum and jejunum main site of absorption freely absorb all products of carbohydrate, protein & fat digestion freely absorb most ingested electrolytes, vitamins & water absorption of calcium & iron is adjusted to the body’s needs Ileum absorbs bile salts, vitamin B12, electrolytes & water Slide 72 of 83 MPharm PHA112 GI System WEEK 14 Slide 73 of 83 Carbohydrate, Protein & fat Digestion MPharm PHA112 GI System WEEK 14 Slide 74 of 83 Carbohydrate Digestion MPharm PHA112 GI System WEEK 14 Carbohydrate Absorption Slide 75 of 83 MPharm PHA112 GI System WEEK 14 Slide 76 of 83 Protein Digestion MPharm PHA112 GI System WEEK 14 Slide 77 of 83 Protein Absorption MPharm PHA112 GI System WEEK 14 Fat Digestion and Absorption Slide 78 of 83 MPharm PHA112 GI System WEEK 14 1. Dietary fat in the form of large fat globules composed of triglycerides is emulsified by the detergent action of bile salts into a suspension of smaller fat droplets. This lipid emulsion prevents the fat droplets from coalescing and thereby increases the surface area available for attack by pancreatic lipase. 2. Lipase hydrolyzes the triglycerides into monoglycerides and free fatty acids. 3. These water-insoluble products are carried to the luminal surface of the small-intestine epithelial cells within water-soluble micelles, which are formed by bile salts and other bile constituents. 4. When a micelle approaches the absorptive epithelial surface, the monoglycerides and fatty acids leave the micelle and passively diffuse through the lipid bilayer of the luminal membranes. 5. The monoglycerides and free fatty acids are resynthesized into triglycerides inside the epithelial cells. 6. These triglycerides aggregate and are coated with a layer of lipoprotein from the endoplasmic reticulum to form water-soluble chylomicrons. 7. Chylomicrons are extruded through the basal membrane of the cells by exocytosis. 8. Chylomicrons are unable to cross the basement membrane of capillaries, so instead they enter the lymphatic vessels, the central lacteals. Slide 79 of 83 MPharm PHA112 GI System WEEK 14 Slide 80 of 83 Iron Absorption MPharm PHA112 GI System The Large Intestine WEEK 14 Consists of the colon, caecum, appendix & rectum Primarily a drying & storage organ Minor absorptive function absorbs water, electrolytes, several vitamin B complexes, vitamin K & folic acid Contains many beneficial bacteria (~500 -1000 sp) produce vitamin K & folic acid ferment indigestible molecules to produce short-chain fatty acids Slide 81 of 83 MPharm PHA112 GI System WEEK 14 Slide 82 of 83 The Large Intestine MPharm PHA112 GI System WEEK Recommended Reading 14 Sherwood L. Human Physiology: From Cells to Systems, 9th ed. International Edition (2015) Sherwood L. Introduction to Human Physiology, 8th ed. International Edition (2013) VanPutte C et al. Seeley's Anatomy & Physiology, 12th ed. International Student Edition (2019) Slide 83 of 83 MPharm PHA112 GI System