Zo Ge tz C h 3 Text b o o k N o t es Nutrition Concepts September 5 2013 Chapter 3 Digestion Absorption and Transport 3 1 Digestion De nitions Digestion the process by which food is broken down into absorbable units Digest take apart Absorption the uptake of nutrients by the cells of the small intestine for transport into either the blood or the lymph Absorb suck in Gastrointestinal tract the digestive tract Principal organs are stomach and intestines Gastro stomach intestinalis intestine Mouth process of digestion starts here First step is mastication Fluids dissolve the food in this process and also help the tongue taste only particles in solution can react with taste buds Tastes include sweet sour bitter and salty Digestive system all the organs and glands associated with the ingestion and digestion of food Bolus a portion with respect to food the amount swallowed at one time Bolus lump Chyme the semiliquid mass of partly digested food expelled by the stomach into the duodenum Chymos juice Peristalsis wavelike muscular contractions of the GI tract that push its contents along Peri around Stellein wrap Segmentation a periodic squeezing or partitioning of the intestine at intervals along its length by its circular muscles Re ux a backward ow Re back ux ow Catalyst a compound that facilitates chemical reactions without itself being changed in the process pH the unit of measure expressing a substance s acidity or alkalinity The lower the pH the higher the acidity or alkalinity The lower the pH the higher the H ion concentration and the stronger the acid A pH above 7 is alkaline or base a solution in which OH ions predominate Stools waste matter discharged from the colon also called feces Explain how foods move through the digestive system describing the actions of the organs muscles and digestive secretions along the way Food enters mouth and travels down the esophagus and through the upper and lower esophageal sphincters to the stomach Date Se p t 8 2 013 Class N ut r it io n Co n ce p t s Page On e Review 3 1 Then travels through the pyloric sphincter to the small intestine on through the ileocecal valve to the large intestine past appendix to the rectum ending at the anus Wavelike contractions of peristalsis and the periodic squeezing of segmentation keep things moving at a reasonable pace Along the way secretions from the salivary glands stomach pancreas liver and small intestine deliver uids and digestive enzymes 3 2 Absorption De nitions Villi ngerlike projections from the folds of the small intestine singular villus Microvilli tiny hairlike projections on each cell of every villus that can trap nutrient particles and transport them into the cells singular microvillus Crypts tubular glands that lie between the intestinal villi and secrete intestinal juices into the small intestine Goblet cells cells of the GI tract and lungs that secrete mucus Travel of foods Contents of digest tract kept moving forward slowly but steadily at a pace that permits completion Food must be lubricated with uids Too much liquid and too rapidly Too little paste and too dry and compact to move at all For digestive enzymes to work food must break down into small particles and in enough liquid so every particle is accessible Once digestion is complete and nutrients have been absorbed from the GI tract into the body the remaining waste must be excreted Excreting all the water along with the solid residue is both wasteful and messy So water is withdrawn and a solid waste product is left that is easy to pass Digestive enzymes designed to digest carbs fat and protein Cells of GI tract made of carbohydrate fat and protein Cells must be protected against powerful digestive juices that they secrete When waste matter reaches end of GI tract must be excreted periodically Review 3 2 Anatomical details of the intestinal cells that facilitate nutrient absorption The many folds and villi of the small intestine dramatically increase its surface area facilitating nutrient absorption Nutrients pass through the cells of the villi and enter either the blood if they are water soluble or small fat fragments or the lymph if they are fat soluble 3 3 The Circulatory Systems De nitions Page 2 Aorta the large primary artery that conducts blood from the heart to the body s smaller arteries Arteries vessels that carry blood from the heart to the tissues Capillaries small vessels that branch from an artery Capillaries connect arteries to veins Exchange of oxygen nutrients and waste materials takes place across capillary walls Veins vessels that carry blood to the heart Hepatic portal vein the vein that collects blood from the GI tract and conducts it to the liver Portal gateway Hepatic vein the vein that collects blood from the liver and returns it to the heart Hepatic liver Review 3 3 Explain how nutrients are routed in the circulatory systems from the GI tract into the body and identify which nutrients enter the blood directly and which must rst enter the lymph Nutrients leaving the digestive system via the blood are routed directly to the liver before being transported to the body s cells Those leaving via the lymphatic system large fats and fat soluble vitamins eventually enter the vascular system but bypass the liver at rst 3 34 The Health and Regulation of the GI Tract De nitions Lymphatic system a loosely organized system of vessels and ducts that convey uids toward the heart The GI part of the lymphatic system carries the products of fat digestion into the bloodstream Lymph a clear yellowish uid that is similar to blood except that it contains no red blood cells or platelets Lymph from the GI tract transports fat and fat soluble vitamins to the bloodstream via lymphatic vessels Thoracic duct the main lymphatic vessel that collects lymph and drains into the left subclavian vein Subclavian vein the vein that provides passageway from the lymphatic system to the vascular system Flora bacteria in the intestines Yogurt milk product that results from the fermentation of lactic acid in milk by lactobacillus bulgaricus and streptococcus thermophilus Probiotics living microorganisms found in foods and dietary supplements that when consumed in suf cient quantitates are bene cial to health Homeostasis the maintenance of constant internal conditions such as blood chemistry temperature and blood pressure by the body s control systems A homeostatic system is constantly reacting to external forces to maintain limits set by the body s
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