HUN3224 Intermediary 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 note the purpose function of each Also list the accessory organs and their purpose function in relation to digestion and absorption The order of the GI tract is as follows Mouth esophagus stomach small intestine large intestine Absorption and digestion is mostly in the small intestine absorption passage of simple molecules across gut wall and into blood or lymph digestion hydrolysis of energy nutrients Elimination of wastes is mostly in the large intestine waste nondigestable carbs and macronutrients and harmful substances Accessory organs Liver pancreas and gallbladder 4 layers of the GI tract Muscularis smooth muscle Inner layer mucosa layer which is composed of 3 parts 1 epithelial lining exocrine secrete enzymes and endocrine secrete hormones glands 2 Lamina Propria has connective tissue lymphatic and blood vessels and lymphoid tissue 3 Lingoid Muscularis mucosa thin layer of smooth muscle contain white blood cells Second Layer Submucosa Layer Connective tissue lymphoid etc Special Submucosa plexus controls movement of whole mucosa and blood flow Third Layer Muscularis Externa Two layers of smooth muscle circular inner and longitudinal outer in between Submucosa and serosa layers has myenteric plexus controls frequency and strength of contractions of the GI tract and regulates GI secretions Outermost Layer Serosa Layer Peritoneum layer that covers all organs in abdominal and pelvic cavities highly vascular 2 Describe how the epithelial lining of the small intestine is structured to enhance surface area to facilitate nutrient absorption The mucosa layer is in large circular folds called Folds of Kerckring which maximizes the surface area and maximizes its ability to absorb nutrients B Digestion 1 For each energy nutrient a Identify major site s of digestion Digestion begins in the mouth first phase is cephalic phase salivation seeing food etc Carbohydrate and lipid digestion occur in the mouth while protein digestion begins in the stomach Carbohydrate digestion does NOT occur in the stomach because the pH of the stomach inactivates salivary amylase so the stomach cannot digest carbs HCl decreases the pH of the stomach Most digestion in the stomach is of PROTEINS Digestion in the lumen is when digestion of carbs is resumed In the lumen Pancreatic amylase breaks down alpha 1 4 bonds of carbs protein digestion pancreatic proteases breaks down proteins into smaller peptides trypsinogen trypsin activates other enzymes fat digestion pancreatic lipase breaks triglycerides into free fatty acids monoacylglycerols and glycerol the emulsification of fats increasing the surface area of fats from bile must occur first co lipase connects triglycerides to enzyme also the formation of micelles Digestion on the brush border all 3 macronutrients mainly carbs the end products of fat digestion must be transported across the unstirred water layer to the brush border by micelles Bile acids and phospholipids in bile engulf FFAs MAGs and free cholesterol because they are not water soluble this is where the end of digestion of carbs occurs Digestion on the intestinal cell protein and lipid digestion b Identify major end products of digestion Carbohydrate end products in the mouth Amylose hydrolyzes alpha 1 4 bonds into maltose and maltotriose amylopectin turns alpha 1 6 links into maltose maltotriose and dextrin Carbohydrate end product in the lumen Hydrolysis of starch to dextrin maltose and maltotriose via pancreatic amylase Carbohydrate end product on the brush border monosaccharides from oligosaccharides via oligosaccharides Lactose glucose and galactose sucrose glucose and fructose dextrin glucose maltose and maltotriose maltose glucose and glucose Protein end product in the stomach some hydrolysis to smaller polypeptides proteoses peptones these are caused by the partial hydrolysis of proteins which would explain why this process is endopeptidase via pepsin an example of an endopeptidase Protein end product in the lumen Hydrolysis of proteins and smaller peptides to di and tripeptides and amino acids via pancreatic proteases Protein end product on the brush border Hydrolysis of oligopeptides via aminopeptidases to tri and di peptides and free amino acids Protein end product in the intestinal cell di and tripeptides are hydrolyzed to amino acids via intracellular cytosolic peptidases Lipid end product in the stomach Limited hydrolysis via lingual gastric lipase Lipid end product in the lumen Hydrolyses of triacylglycerols TAG to monoacylglycerols MAGs free fatty acids FFAs and glycerol then engulfed by bile acids and phospholipids into micelles Lipid end product in the intestinal cell Long chain FAs and MAGs synthesized into TAGs Cholesterol is esterified CE TAGs CE free cholesterol and phospholipids incorporated into chylomicrons lipoprotein particles that consist of triglycerides phospholipids cholesterol and proteins They transport dietary lipids from the intestines to other locations in the body 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 A 1 Salivary Amylase 2 Hydrolyzes alpha 1 4 bonds into maltose and maltotriose 3 Saliva 4 The oral cavity B 1 Pancreatic Amylase 2 Hydrolyzes alpha 1 4 bonds hydrolysis of starch to dextrin maltose and maltotriose 3 Pancreas Digestive enzymes produced by acinar exocrine cells in the pancreas 4 Lumen These enzymes Oligosaccharidases enzymes are inhibited by their end products C 1 Lactase 2 Converts lactose to glucose and galactose 3 4 Brush border microvilli D 1 Sucrase 2 Converts sucrose to glucose and fructose 3 4 Brush border microvilli E 1 Dextrinase 2 Converts dextrin to glucose maltose and maltriose 3 4 Brush border microvilli F Maltase 2 Converts maltose to glucose and glucose 3 4 Brush border microvilli Lipids A 1 Lingual Lipase 2 Hydrolysis of milk fat 3 Saliva 4 The oral cavity B 1 Lingual Gastric Lipase note lingual lipase continues from the oral cavity both lingual lipase and salivary amylase are part of the bolus to continue to the stomach 2 Limited hydrolysis of TAG s to MAG
View Full Document
Unlocking...