nutrition e5 chapter 03
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Digestion and Absorption
Chapter
3
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Taste and Smell: The Beginnings of Our Food Experience
• The Chemosenses• Olfactory cells• Gustatory cells• Common chemical sense• Cephalic phase responses
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The Gastrointestinal Tract• Organization
• Mouth to anus• Accessory organs
• Salivary glands, liver, pancreas, gallbladder
• Functions• Ingestion• Transport• Secretion• Digestion• Absorption• Elimination
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Overview of Digestion
• Physical movement• Peristalsis• Segmentation
• Chemical breakdown• Enzymes• Other secretions
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Overview of Absorption• Absorptive mechanisms
• Passive diffusion• Facilitated diffusion• Active transport
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Assisting Organs
• Salivary glands• Moisten food• Supply enzymes
• Liver• Produces bile
• Gallbladder• Stores and secretes bile
• Pancreas• Secretes bicarbonate• Secretes enzymes
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Putting It All Together: Digestion and Absorption
• Mouth• Enzymes
• Salivary amylase acts on starch• Lingual lipase acts on fat
• Saliva• Moistens food for swallowing
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Putting It All Together: Digestion and Absorption
• Stomach• Hydrochloric acid
• Prepares protein for digestion• Activates enzymes
• Pepsin• Begins protein digestion
• Gastric lipase• Some fat digestion
• Gastrin (hormone)• Stimulates gastric secretion and movement
• Intrinsic factor• Needed for absorption of vitamin B12
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Putting It All Together: Digestion and Absorption
• Small intestine• Sections of small intestine
• Duodenum, jejunum, ileum• Digestion
• Bicarbonate neutralizes stomach acid
• Pancreatic & intestinal enzymes
• Carbohydrates• Fat• Protein
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Putting It All Together: Digestion and Absorption
• Small intestine• Absorption
• Folds, villi, microvilli expand absorptive surface• Most nutrients absorbed here• Fat-soluble nutrients go into
lymph• Other nutrients into blood
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Putting It All Together: Digestion and Absorption
• Large intestine• Digestion
• Nutrient digestion already complete• Some digestion of fiber by bacteria
• Absorption• Water• Sodium, potassium, chloride• Vitamin K (produced by bacteria)
• Elimination
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Regulation of GI Activity
• Nervous system• Regulates GI activity
• Local system of nerves• Central nervous system
• Hormonal system• Increases or decreases GI activity
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Circulation of Nutrients
• Vascular system• Lymphatic system
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Influences on Digestion and Absorption
• Psychological Influences• Chemical Influences• Bacterial Influences
© Corbis
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Nutrition and GI Disorders
• Constipation• Hard, dry, infrequent stools• Reduced by high fiber, fluid intake,
exercise• Diarrhea
• Loose, watery, frequent stools• Symptom of diseases/infections• Can cause dehydration
• Diverticulosis• Pouches along colon• High-fiber diet reduces formation
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Nutrition and GI Disorders
• Heartburn and Gastroesophageal Reflux • Reduced by smaller meals, less fat
• Irritable Bowel Syndrome (IBS)• Colorectal cancer• Gas• Ulcers
• Bacterial cause• Dyspepsia
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Cephalic Phase Responses
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Sphincters in Action
• Movement from one section of the GI tract to the next is controlled by muscular valves called sphincters.
• When closed, the sphincter prevents the backflow of material from the duodenum to the stomach.
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Peristalsis and Segmentation
• Peristalsis and segmentation help to break up, mix, and move food through the GI tract.
• Periodic muscle contractions at intervals along the GI tract that alternate forward and backward movement of contents, thereby breaking apart chunks of the food mass and mixing in digestive juices.
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Enterohepatic Circulation• During this recycling
process, bile travels from the liver to the gallbladder and then to the small intestine, where it assists digestion.
• In the small intestine, most of the bile is reabsorbed and sent back to the liver for reuse.
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Down the Wrong Pipe
• When you swallow, the epiglottis closes off the air passage and prevents choking.
• If you have ever had a drink go “down the wrong pipe” and you choked, likely, your epiglottis didn’t completely do it’s job.
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The Stomach
• The stomach churns and mixes food with stomach secretions.
• Hydrochloric acid unfolds protein and stops salivary amylase action.
• Pepsin begins protein digestion.• The pyloric sphincter controls
movement of chyme from stomach to the small intestine.
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Lactose Intolerance
• Of all the world’s populations, Native Americans have the highest level of lactose intolerance, with 100 percent intolerance.
• Ninety-eight percent of Southeast Asians are intolerant, while only 2 percent of the Swedish population are intolerant.
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Short Bowel Syndrome
• Those who suffer from short bowel syndrome have difficulty absorbing fat-soluble vitamins.
• To enhance absorption, treatment includes taking a fat-soluble vitamin supplement that easily mingles with water.
• These patients may also need to take intramuscular shots of B12 because they are unable to absorb this water-soluble vitamin.
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Chewing Gum and Colon Surgery• In a new study, it has been
observed that chewing gum immediately following abdominal surgery, including colon surgery, can cause a marked decrease or stoppage of intestinal function (ileus).
• Ileus can lead to a longer hospital stay, increased risk of infection, and breathing difficulties.
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Gastrointestinal Flora Abound
• Your entire body has about 100 trillion cells, but this is only one-tenth the number of protective microorganisms normally living in your body.
• More than 500 bacterial species alone live in your GI tract.