Nutrition Concepts !Zoë Getz - Ch. 3 Textbook Notes September 5, 2013 !Chapter 3: Digestion, Absorption, and Transport 3.1 Digestion:! !Definitions: !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 !Reflux: a backward flow. Re= back, flux=flow !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 !!Review 3.1: !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 Sept 8, 2013 Class Nutrition Concepts Page One!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 fluids and digestive enzymes. !3.2 Absorption:! !Definitions: !!Villi: fingerlike 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 fluids. 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: !Definitions: 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 first 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 first. !3.34 The Health and Regulation of the GI Tract: !!Definitions: !Lymphatic system: a loosely organized system of vessels and ducts that convey fluids toward the heart. The GI part of the lymphatic system carries the products of fat digestion into the bloodstream. !Lymph: a clear yellowish fluid 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
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