Chapter 3 Digestion and Absorption Dr Alisha Rovner University of Delaware Nutrition Concepts NTDT200 Fall 2013 Lecture Overview 1 Digestion 2 Absorption 3 Common Digestive Problems Learning Objectives Explain how foods move through the digestive system Describe the anatomical details of the intestinal cells that facilitate nutrient absorption Discuss common GI problems and their treatments Digestion take apart Body s way of breaking down foods into nutrients to prepare for absorption Challenges of digestion Tasks of the mouth Diaphragm swollaing and breathing Steady movement Lubrication of food enzyme Digestive enzyme functions Excretion of waste Anatomy of the Digestive Tract Gastrointestinal GI tract Flexible and muscular tube Mouth esophagus stomach small intestine large intestine rectum anus Lumen inner space within GI tract Continuous from one end until the other The Gastrointestinal Tract Anatomy of the Digestive Tract Mouth Process of digestion begins here Mastication process of chewing When stimulated taste buds detect 4 basic taste sensations sweet sour bitter salty Swallowed food passes through pharynx Epiglottis closes off airway so choking doesn t occur when swallowing After mouth full of food has been chewed and swallowed it s called a bolus Esophagus conduit from mouth to stomach Two sphincters 1 at each end Upper esophageal sphincter opens during swallowing Lower esophageal sphincter at the entrance to the stomach function closes behind bolus so doesn t slip back Anatomy of the Digestive Tract Stomach Movement of bolus retains it for awhile then transfers it to its lower portion Chyme semiliquid mass released through pyloric sphincter Pyloric sphincter opens into small intestines and closes behind chyme Anatomy of the Digestive Tract Small intestine Chyme Bypasses the opening from bile duct Travels through three segments of small intestines duodenum jejunum and ileum Large intestine colon Remaining contents arrive at ileocecccal value As contents pass to the rectum the colon withdraws water Waste is held until it s time to get rid of it Muscular Action of Digestion Segmentation Contraction of circular muscles in small intestine Mix chyme digestion food Promote contact with absorption cells Sphincter contractions Periodically open and close Control pace of GI tract contents not too slowly or quickly Muscular Action of Digestion Peristalsis Circular and longitudinal muscles working together Rate and intensity of contractions vary age and disease weight can infuence this Factors that may interfere with peristalsis Stomach action Circular longitudinal and diagonal muscles Timing the release of chyme Muscular Action of Digestion Segmentation Contraction of circular muscles in small intestine Mix chyme Promote contact with absorption cells Sphincter contractions Periodically open and close Control pace of GI tract contents Secretions of Digestion Breakdown of food into nutrients requires secretions from 5 organs Salivary glands in the mouth carbohydrte stomach protein pancreas car protein fat liver fat small intestine all three macro Secretions enter GI tract at various points Water Enzymes Protein facilitator of chemical reactions Hydrolysis Secretions of Digestion Saliva Moisten food for easy passage Protective role for teeth linings of mouth esophagus and stomach Initiates carbohydrate digestion begin Gastric juice Acts primarily in protein digestion Cells of stomach secrete mucus for protection pH 2 Secretions of Digestion Pancreatic juice and intestinal enzymes Released via ducts into duodenum Enzymes act on all three energy nutrients Sodium bicarbonate Bile Liver Gallbladder Summary of Digestive Secretions Their Major Actions Digestive Fate of Sandwich The Final Stage Undigested residues Exercise intestinal muscles Retention of water Colon Intestinal bacteria Recyclable materials Water and dissolved salts Absorption Small intestine Majority of absorption occurs here Ten feet long surface area Absorption techniques diff type nutrient Simple diffusion cross into intestines freely Facilitated diffusion need specific carrier to transport them from one side of cell membrane to another Active transport move against a concentration gradient requires energy Absorption of Nutrients 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 78 Anatomy of the Absorptive System Villi Fingerlike projections from folds of small intestines Select and regulate nutrients absorbed Microvilli Hairlike projections on each cell of every villus Traps nutrient participates and transports them into the cells Anatomy of the Absorptive System Anatomy of the Absorptive System Crypts Tubular glands that lie between intestinal villi Secrets intestinal juices into small intestine Goblet cells Cells of GI tract Secretes mucus Myth of Food Combining People shouldn t eat certain foods in combination because the digestive system can t handle it is a MYTH Foods eaten together can often enhance each other eg Vitamin C in citrus fruit can enhance iron absorption from iron containing foods Common Digestive Problems Highlight 3 Choking Food slips into trachea Cuts off breathing Foods commonly associated with choking Hot dogs whole grapes hard candy popcorn Young children 4 yrs old at risk Prevention of choking Normal Swallowing and Choking First Aid for Choking Vomiting Vomiting Adaptive mechanism of the body to try to rid itself of something irritating Medical treatment Rest and drink small amounts of liquids If large quantities of liquids lost causing hydration may be serious May be serious in infants Diarrhea Diarrhea Symptom of medical conditions treatments May occur in healthy people as result of
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