HUN3224 - Intermediate Metabolism of Nutrients IExam 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 electrolyteso Movement called halstrationo Fecal matter stay in ascending colon for nutrient absorption could take 10-72 hourso Microorganisms act on energy nutrients not previously digested/absorbed in S.I to form: fermentation macronutrients absorbed in L.I.- GasesEx: 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 Organso Pancreas: two types of cells in pancreas are: ductless endocrine cells that secrete hormones (primarily insulin and glucagon) and acinar exocrine cells that produce the digestiveenzymes, 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 digestiveenzymes in a watery solution.o Liver: 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 hepatocyteso Gallbladder: located on the surface of the liver. Gallbladder concentrates and stores the bile madein 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 thedigestive tract and aid in the digestive and absorptive processes. 2. Describe how the epithelial lining of the small intestine is structured to enhance surfacearea 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 villiB. 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 disaccharideso use of carbs depends on absorption from GI tract into bloodstream, normally restricted to monosaccharideso polysaccharides & disaccharides must be hydrolyzed to their constituent monosaccharide unitso major site of digestion: mouth, stomacho 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 hydrolyzedo Major end products: (in lumen) Hydrolysis of starch to dextrins (short chain polysaccharides), maltose and maltotriose 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 galactoseo Sodium- dependent (symport transport); active transport- Fructoseo Sodium independent (GLUT 5); facilitated diffusiono GLUT 5 may also transport some glucose- Sucrose and maltose alpha bonds- Lactose beta bondso 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 environmento Dietary lipid targeted for digestion is emulsified by efficient process, mediated by bile saltso Esterases cleave ester bonds within triacylgelcyerols, phospholipids, and cholesterol esterso digestion in stomach and small intestineo in stomach, lingual lipase and gastric lipase (produced by chief cells). Secretion can be stimulated by neural, dietary, and mechanical factorso most TAG digestion occurs in small intestineo 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
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