anim_carbohydrate_digestion_absorption_answer_key.doc

The Carbohydrate Digestion & Absorption To complete this worksheet, select: Module: Energy Acquisition Activity: Animations Title: Carbohydrate Digestion & Absorption Introduction 1. Generally describe how the following are involved with digestion. Digestion of complex carbohydrates involves amylases produced by the salivary gland and pancreas, and brush-border enzymes in the small intestine. Carbohydrate Digestion 2. a. Where does carbohydrate digestion begin? Carbohydrate digestion begins in the mouth. b. What enzyme and glands are involved? The parotid and submandibular salivary glands are involved with the secretion of salivary amylase. 3. How does salivary amylase affect starch and glycogen (two complex carbohydrates)? Salivary amylase converts starch and glycogen into maltose, maltotriose and alpha-dextrins. 4. Why are only a few starch or glycogen molecules completely digested to maltose (a simple sugar) by the time they enter the stomach? Only a few starch or glycogen molecules are completely digested into maltose before they enter the small intestine because the acidic pH of the stomach destroys the salivary amylase. 5. a. How does the pancreas contribute to carbohydrate digestion? The pancreas also secretes amylase into the small intestine. b. Where does pancreatic amylase do its work? How has the pH been adjusted so this enzyme is functional? In the small intestine, bicarbonate ions from the pancreatic juice neutralize the acidic chyme and amylase continues the breakdown of starches and glycogen into maltose, maltotriose and alpha-dextrins. c. How do we digest cellulose (a complex plant carbohydrate)? (Be careful, this is a little tricky.) We are incapable of digesting cellulose. Cellulose requires the enzyme cellulose which we, as humans, do not synthesize or produce. 6. Where is carbohydrate digestion completed? Carbohydrate digestion is completed in the microvilli of the small intestine. 7. Four brush-border enzymes are involved in completing carbohydrate digestion. Describe what each of them achieve. Alpha-dextrinase - breaks down alpha-dextrin chains by removing glucose units. Sucrase - sucrase breaks down sucrose into glucose and fructose. Maltase Maltase breaks down maltose into glucose Lactase - breaks down lactose into glucose and galactose. Carbohydrate Absorption 8. a. Specifically, what is absorbed into the blood following carbohydrate digestion? All end products of carbohydrate digestion are absorbed. This includes, glucose, fructose and galactose. b. Specifically, where does this absorption occur? Carbohydrates are ultimately absorbed into the capillaries of the villi. 9. Describe facilitated transport of the monosaccharide fructose. Facilitated transport or diffusiion, a process that involves the use of carrier molecules to move substances across the membrane down its concentration gradient, transports fructose from the lumen into epithelial cells of the intestinal villi. It also transports monosaccharides out of the epithelial cells into the interstitial fluid. The monosaccharides eventually diffuse into the blood stream without using ATP in the process. 10. a. Describe secondary active transport of glucose and galactose. Glucose and galactose are transported into the epithelial cells of the intestinal villi. The secondary active transport mechanism couples the transport of glucose or galactose with that of sodium ions and transports the materials in the same direction as one of the substances down the concentration gradient. b. Facilitated diffusion (transport) finishes glucose and galactose absorption into the blood. Explain. Glucose and galactose are then transported from the epithelial cells to the interstitial fluid and eventually into the bloodstream via facilitated diffusion.