Harvard-MIT Division of Health Sciences and Technology HST.121: Gastroenterology, Fall 2005 Instructors: Dr. Jonathan Glickman Overview of GastroenterologyGastroenterology Made Really Simple! Food Waste NutrientsThe Basic Structure Image removed due to copyright reasons.The Propulsion System: Driven by the Muscles Food Waste Nutrients Periodic phasic contractions Local tonic contractions (sphincters)The Neural Control System: The Brain in the Gut Muscularis Mucosae Longitudinal muscle Circular muscle Mucosa Submucosal plexus Myenteric plexus (Vagus/Pelvic) ACh NENE NEACh ACh Parasympathetic nerves Sympathetic gangliaThe Neurocrine Effectors Decreased intestinal secretions Neuropeptide Y Decreased intestinal secretions Vasoactive intestinal peptice (VIP) Norepinephrine (NE) •Smooth muscle contraction •• Acetylcholine (ACh) • ActionsPeptide Smooth muscle relaxation Smooth muscle contraction Increased salivary secretions Substance P Smooth muscle contraction Enkephalins Increased gastrin secretion Gastrin-releasing peptide (GRP, bombesin) Smooth muscle relaxaton Increased intestinal and pancreatic secretions Smooth muscle relaxation Sphincter contraction Increased salivary secretion Sphincter relaxation Increased salivary, gastric, and pancreatic secretionsThe hormonal control system Satiety (CNS)L cells jejunum)Oral glucose FastingGhrelin Pancreatic enzyme, HCO3 secretionS cellsSecretin Pancreatic enzyme, HCO3 secretion Gallbladder contraction I cells jejunum) (CCK) Growth of gastric mucosa G cells (stomach) Gastric distension Gastrin ActionsSite of secretionHormone Inhibition of acid secretion Stimulation of insulin secretion (duodenum and Fatty acids, amino acids Glucagon-like peptide (GLP-1) Stimulates appetite (CNS) Stomach Inhibition of gastrin, acid secretion (duodenum) Fatty acids Duodenal motility Inhibition of gastric emptying (duodenum and Fatty acids Peptide and amino acids Cholecystokinin Stimulation of gastric acid secretion Vagal stimulation Peptide and amino acids StimuliGut-brain hormonal interactions Image removed due to copyright reasons.Salivary Secretion Acinus K, HCO3 Na, Cl Na Na H K H K Cl Cl HCO3 Alpha-Amylase Kallikrein Mucus Electrolytes Duct Hypotonic salivaGastric Secretions Pepsinogen Gastric Lipase IF Mucus Hormones Parietal cells Chief cells NE cells HCl Mucous cellsBiliary Secretion Cholesterol & bile acids Bile acids Water and electrolytes (CCK) Water and electrolytes (Secretin)Pancreatic Secretions Alpha-Amylase Na LipasesAcinus Proteases Centroacinar H K Cl HCO3 H2CO3 H2O + CO2 Carbonic Anhydrase NaCells Duct Bicarbonate Basic Pancreatic Secretions Na ParacellularCarbohydrate Digestion 1:4 glucosidic link 1:6 glucosidic link Maltose Alpha-limit dextrin Maltotriose Alpha-amylase breaks 1:4 linkages except at either end of starch molecules. This results in the production of three simple sugars as shown above.Overview of Carbohydrate Digestion Starch Maltose Dextrin Maltotriose Maltase Sucrase Glucose Lactase Dextrinase Glucose Galactose Lactose Glucose Fructose Sucrose SucraseOverview of Protein Digestion Low pH Pepsinogen Pepsin B. B. Enterokinase Trypsinogen Trypsin Trypsin Trypsinogen Trypsin Trypsin Chymotryp. Chymotrypsin Trypsin Proelastase Elastase Trypsin Procarboxy. CarboxypeptidaseOverview of Protein Digestion Stomach Small Intestine Proteins Oligopeptides Amino acids Amino acids Dipeptides Tripeptides B. B. Peptidases Pepsin Proteins Amino acids Oligopeptides Trypsin, et al.Overview of Lipid Digestion Triglycerides Chol. Ester Monoglyceride Fatty Acids Fatty Acids Fatty AcidsCholesterolLysolecithin Lipases Phospholipase A2 Chol. ester hydrolase