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Digestion Absorption and Transport • Digestion the process of breaking down food into its basic components so they can be absorbed • CHO, fat, pro are hydrolysed • Vits, mins, water aren’t (Chapter 3) Digestion Your GI tract is like a tube! Food travels through the lumen while it gets digested Digestion • Two types of action: • Mechanical • Chemical 1 Peristalsis Sphincters: open and close 2 GI Tract Signals • Food, pH, nerves, hormones • Enterogastrones: • Gastrin • CCK • Secretin Segmentation Accessory Organs Emulsification of Fat by Bile Absorption • Taking up nutrients from lumen into the cells 3 Absorption • The huge surface area of the small intestine facilitates nutrient absorption • Folds, Villi, and Microvilli • (Oh my!) Absorption • Nutrients can be absorbed through simple diffusion, facilitated diffusion, or active transport. Carrier loads nutrient on outside of cell . . . Outside cell Carrier loads nutrient on outside of cell . . . Cell membrane Inside cell . . . and then releases it on inside of cell. SIMPLE DIFFUSION Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely. FACILITATED DIFFUSION Some nutrients (such as the watersoluble vitamins) are absorbed by facilitated diffusion. They need a specific carrier to transport them from one side of the cell membrane to the other. (Alternatively, facilitated diffusion may occur when the carrier changes the cell membrane in such a way that the nutrients can pass through.) . . . and then releases it on inside of cell. ACTIVE TRANSPORT Some nutrients (such as glucose and amino acids) must be absorbed actively. These nutrients move against a concentration gradient, which requires energy. Stepped Art Fig. 3-9, p. 81 4 Transverse colon Opening from small intestine to large intestine Ascending colon End of small intestine Descending colon Appendix Rectum Anus Sigmoid colon Stepped Art Fig. 3-7, p. 78 Where’s the Fiber? • Undigested residues, including some fibers, continue through the digestive tract and form stool. Gastrointestinal Bacteria A healthy GI tract has many different non-disease-causing bacteria known as flora or microflora. BTW “Food combining” which emphasizes separating food for digestive purposes is a myth! • Probiotics are bacteria found in the GI tract that can be beneficial to health. • Prebiotics are foods (e.g. fiber) that are used as food by intestinal bacteria. • Bacteria produce vitamins! 5 Next step: Transport • Once nutrients cross into the villi, they are transported to the rest of the body • Through blood and lymph systems Preparing for Transport Water-soluble nutrients and small products of fat digestion are released to the bloodstream. First stop is liver. Fat-soluble vitamins and larger fats form chylomicrons before being released to the lymphatic system. Then via thoracic duct to blood. Common Digestive Problems 6 Heartburn and “Acid Indigestion” Belching and Gas • Strategies • • • • Eat slowly. Chew thoroughly. Relax while eating. Watch bothersome foods. • Gastroesophageal reflux (GERD) is the backward flow of stomach contents into the esophagus. • Antacids and acid controllers may help indigestion. • Hiccups are triggered by eating or drinking too fast. Heartburn and “Acid Indigestion” • Strategies • • • • • • • • • Ulcers • Peptic ulcers can be gastric or duodenal. • Strategies • Take prescribed medicine. • Avoid caffeine- and alcoholcontaining foods. • Minimize aspirin and ibuprofen use. • No smoking. Small meals Liquids in-between meals Sit up while eating. Wait 1 hour after eating before lying down. Wait 2 hours after eating before exercising. Refrain from tight-fitting clothing. Avoid bothersome foods. Refrain from tobacco use. Lose weight if overweight. Diarrhea • Frequent, loose, watery stools • Strategies • • • • Rest Drink fluids BRAT diet Medical help is needed if it persists. 7 Constipation Possible complications: • Hemorrhoids • Diverticulosis is a condition in which the intestinal walls weaken and bulge. The bulging pockets are called diverticula. • Diverticulitis is when they are inflammed and requires intervention. Constipation • Prevention Strategies • • • • High-fiber diet Increased fluids Exercise regularly. Respond quickly to the urge to defecate. 8