HUN3224 Intermediate Metabolism of Nutrients I Exam I Study Guide Digestion and Absorption of Carbohydrates Lipids and Proteins A Physiology of the gastrointestinal GI tract 1 List the parts of the GI tract in the proper sequence and not the purpose function of each Also list the accessory organs and their purpose function in relation to digestion and absorption Oral cavity salivary amylase breaks down carbs and lingual lipase breaks down milk fat lysozymes kill bacteria mastication takes place here which increases surface area Esophagus muscular tube that connects the back of the mouth and stomach movement of food is via peristalsis lower esophageal sphincter relaxes to let food into the stomach and constricts to keep food from moving back into the esophagus Stomach collectively referred to as the upper digestive tract holds food mechanical mixing and breaking down of food gastric secretions absorption of alcohol and aspirin Small intestine 3 sections are duodenum jejunum and ileum digestive events occur in the lumen on the brush border and in the intestinal cell major GI hormones released by duodenum Large intestine Colon large intestine o Absorption of water and electrolytes o Movement called halstration o Fecal matter stay in ascending colon for nutrient absorption could take 10 72 hours o Microorganisms act on energy nutrients not previously digested absorbed in S I to form fermentation macronutrients absorbed in L I Gases Ex CO2 methane hydrogen fart Pyloric Sphincter circular muscular separating stomach and duodenum regulates movement of food and acid from stomach to small intestine chyme acid food Accessory Organs o Pancreas o Liver o Gallbladder two types of cells in pancreas are ductless endocrine cells that secrete hormones primarily insulin and glucagon and acinar exocrine cells that produce the digestive enzymes packed in granules and released by exocytosis into pancreatic juice Pancreatic juice produced by acinar cells contains bicarbonate neutralizes acid chyme passing into duodenum from stomach electrolytes and pancreatic digestive enzymes in a watery solution largest single internal organ of the body is made up of right and left lobes functional units lobules made up of sheets or plates of liver cells called hepatocytes located on the surface of the liver Gallbladder concentrates and stores the bile made in the liver until it is needed for fat digestion in the small intestine hormone cholecystokinin secreted into blood by enteroendocrine cells of proximal small intestine stimulates gallbladder to contract and release bile into duodenum Somatostatin works in paracrine fashion inhibits gallbladder contraction The accessory organs provide or store secretions that ultimately are delivered to the lumen of the digestive tract and aid in the digestive and absorptive processes 2 Describe how the epithelial lining of the small intestine is structured to enhance surface area to facilitate nutrient absorption Villi project out lumen of intestine and consist of enterocytes absorptive epithelial cells with capillaries and a central lacteal for transport of nutrients out of enterocyte Possess a coat or glycocalyx to make up the brush border of enterocytes Large circular folds of mucosa protrude into lumen of small intestine Microvilli hairlike extensions of plasma membrane of enterocytes make up villi B Digestion 1 For each energy nutrient a Identify major site s of digestion b Identify major end products of digestion c Describe the sequence of events in the digestion of each energy nutrient being certain to 1 Name the enzymes involved 2 Describe the function of each enzyme 3 identify the source of the enzyme e g pancreas 4 And identify the site of action for the enzyme e g lumen of S I Carbohydrates o most important nutritionally are polysaccharides and disaccharides o use of carbs depends on absorption from GI tract into bloodstream normally restricted to monosaccharides o polysaccharides disaccharides must be hydrolyzed to their constituent monosaccharide units o major site of digestion mouth stomach o key enzyme Salivary alpha amylase a glycosidase to hydrolyze alpha 1 4 glycosidic linkages continues in stomach until gastric acid penetrates food bolus and lowers pH to inactivate enzyme at this point starches are partially hydrolyzed o Major end products in lumen maltotriose Hydrolysis of starch to dextrins short chain polysaccharides maltose and Further digestion of dextrin in small intestine by alpha amylase of pancreatic origin secreted into duodenal contents Amylopectin dextrin maltose maltotriose via amylase Amylose maltose maltotriose via amylase o Digestion in brush border Hydrolysis of oligosaccharides to monosaccharides via oligosaccharidases inhibited by end products of reaction Monosaccharides transported across brush border via carriers Glucose and galactose Fructose o Sodium dependent symport transport active transport o Sodium independent GLUT 5 facilitated diffusion o GLUT 5 may also transport some glucose Sucrose and maltose alpha bonds Lactose beta bonds o As you grow beta bonds diminish and result in lactose intolerance Oligosaccharide Digestion Lactose glucose galactose via lactase Sucrose fructose glucose sucrose Dextrin maltose maltotriose glucose via dextrinase Maltose glucose glucose maltase Fats triacylglycerol o Digestive enzymes are hydrophilic and function in aqueous environment o Dietary lipid targeted for digestion is emulsified by efficient process mediated by bile salts esters o Esterases cleave ester bonds within triacylgelcyerols phospholipids and cholesterol o digestion in stomach and small intestine o in stomach lingual lipase and gastric lipase produced by chief cells Secretion can be stimulated by neural dietary and mechanical factors o most TAG digestion occurs in small intestine o In Lumen Hydrolysis of TAG to monoglycerols MAG FFA and glycerol via pancreatic lipase Emulsification of fats via bile acids bile salts increase surface area of fats Co lipase provides lipase access to TAG Lipase can function in low pH of gastric juices Formation of micelles Bile acids phospholipids in bile engulf FFA s MAG s and free End products of fat digestion transported across unstirred water layer to cholesterol brush border Bile Concentrated and stored in gall bladder Synthesized in the liver o In Intestinal cells Longchain Fas and MAGs synthesized into TAGs Esterify cholesterol CE TAGs CE free cholesterol and phospholipids incorporated into
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