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. Outside cell Cell membrane Inside cell SIMPLE DIFFUSION Carrier loads nutrient on outside of cell... FACILITATED DIFFUSION... and then releases it on inside of cell. Carrier loads nutrient on outside of cell... ACTIVE TRANSPORT... and then releases it on inside of cell. Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely. 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.) 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 Appendix Ascending colon End of small intestine Descending colon 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. 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! BTW Food combining which emphasizes separating food for digestive purposes is a myth! 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
Belching and Gas Strategies Eat slowly. Chew thoroughly. Relax while eating. Watch bothersome foods. Hiccups are triggered by eating or drinking too fast. Heartburn and Acid Indigestion Gastroesophageal reflux (GERD) is the backward flow of stomach contents into the esophagus. Antacids and acid controllers may help indigestion. Heartburn and Acid Indigestion Strategies 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. Ulcers Peptic ulcers can be gastric or duodenal. Strategies Take prescribed medicine. Avoid caffeine- and alcoholcontaining foods. Minimize aspirin and ibuprofen use. No smoking. 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