Harvard-MIT Division of Health Sciences and Technology HST.121: Gastroenterology, Fall 2005 Instructors: Dr. Jonathan Glickman Overview of Gastroenterology
Gastroenterology Made Really Simple! Food Waste Nutrients
The Basic Structure Image removed due to copyright reasons.
The Propulsion System: Driven by the Muscles Periodic phasic contractions Food Waste Nutrients Local tonic contractions (sphincters)
The Neural Control System: The Brain in the Gut ACh Mucosa NE NE Muscularis Mucosae Submucosal plexus ACh Circular muscle NE Myenteric plexus ACh Longitudinal muscle Parasympathetic nerves (Vagus/Pelvic) Sympathetic ganglia
The Neurocrine Effectors Peptide Actions Acetylcholine (ACh) Norepinephrine (NE) Vasoactive intestinal peptice (VIP) Gastrin-releasing peptide (GRP, bombesin) Smooth muscle contraction Sphincter relaxation Increased salivary, gastric, and pancreatic secretions Smooth muscle relaxation Sphincter contraction Increased salivary secretion Smooth muscle relaxaton Increased intestinal and pancreatic secretions Increased gastrin secretion Enkephalins Substance P Neuropeptide Y Smooth muscle contraction Decreased intestinal secretions Smooth muscle contraction Increased salivary secretions Smooth muscle relaxation Decreased intestinal secretions
The hormonal control system Hormone Stimuli Site of secretion Actions Gastrin Vagal stimulation Gastric distension Peptide and amino acids G cells (stomach) Stimulation of gastric acid secretion Growth of gastric mucosa Cholecystokinin (CCK) Fatty acids Peptide and amino acids I cells (duodenum and jejunum) Pancreatic enzyme, HCO3 secretion Gallbladder contraction Inhibition of gastric emptying Secretin Fatty acids Duodenal motility S cells (duodenum) Pancreatic enzyme, HCO3 secretion Inhibition of gastrin, acid secretion Ghrelin Fasting Stomach Stimulates appetite (CNS) Glucagon-like peptide (GLP-1) Fatty acids, amino acids Oral glucose L cells (duodenum and jejunum) Satiety (CNS) Inhibition of acid secretion Stimulation of insulin secretion
Gut-brain hormonal interactions Image removed due to copyright reasons.
Salivary Secretion Acinus Alpha-Amylase Kallikrein Mucus Electrolytes Na H Cl Na Duct Na, Cl K, HCO 3 HCO 3 H K Cl K Hypotonic saliva
Gastric Secretions Mucous cells Mucus Pepsinogen Gastric Lipase NE cells HCl IF Parietal cells Chief cells Hormones
Biliary Secretion Water and electrolytes (CCK) Water and electrolytes Cholesterol & bile acids (Secretin) Bile acids
Pancreatic Secretions Acinus Alpha-Amylase Lipases Proteases K Na Centroacinar Cells Cl Na Duct HCO 3 H Bicarbonate Carbonic Anhydrase H 2 CO 3 Basic Pancreatic Secretions Na H 2 O + CO 2 Paracellular
Carbohydrate Digestion 1:6 glucosidic link 1:4 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 Dextrinase Lactose Lactase Sucrose Sucrase Maltase Glucose Sucrase Glucose Galactose Glucose Fructose
Overview of Protein Digestion Pepsinogen Pepsin Low ph Trypsinogen Trypsin B. B. Enterokinase Trypsinogen Chymotryp. Proelastase Procarboxy. Trypsin Trypsin Trypsin Trypsin Trypsin Chymotrypsin Elastase Carboxypeptidase
Overview of Protein Digestion Stomach Small Intestine Proteins Proteins Pepsin Trypsin, et al. Amino acids Oligopeptides Oligopeptides Amino acids Amino acids Dipeptides Tripeptides B. B. Peptidases
Overview of Lipid Digestion Triglycerides Phospholipids Chol. Ester Lipases Phospholipase A 2 Chol. ester hydrolase Monoglyceride Fatty Acids Lysolecithin Fatty Acids Cholesterol Fatty Acids