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Digestion, Absorption, and Transport
Chapter 3
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Digestion Breaking down foods into nutrients Challenges of digestion
Prepare for absorption Challenges of digestion Tasks of the mouth Diaphragm Steady movement Lubrication of food Digestive enzyme functions
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Anatomy of the Digestive Tract
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Anatomy of the Digestive Tract
Gastrointestinal (GI) tract Flexible and muscular Path Mouth → esophagus → stomach → small intestine → large intestine → rectum → anus Lumen Continuous
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Anatomy of the Digestive Tract
Mouth Process of digestion begins Mastication Four basic taste sensations Savory Aroma, texture, and temperature Pharynx Bolus
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Anatomy of the Digestive Tract
Esophagus Two sphincters Upper esophageal sphincter Lower esophageal sphincter Stomach Movement of bolus Chyme Pyloric sphincter
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Anatomy of the Digestive Tract
Small intestine Common bile duct Pancreas and gall bladder Three segments Large intestine (colon) Ileocecal valve Withdrawal of water Rectum and anus
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Anatomy of the Digestive Tract
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Opening from small intestine to large intestine Descending colon
Transverse colon Ascending colon End of small intestine Opening from small intestine to large intestine Figure 3.2: The Colon. The colon begins with the ascending colon rising upward toward the liver. It becomes the transverse colon as it turns and crosses the body toward the spleen. The descending colon turns downward and becomes the sigmoid colon, which extends to the rectum. Along the way, the colon mixes the intestinal contents, absorbs water and salts, and forms stools. Descending colon Appendix Rectum Sigmoid colon Anus Stepped Art Fig. 3-2, p. 72
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Muscular Action of Digestion
Peristalsis Circular and longitudinal muscles working together Rate and intensity of contractions vary Factors that may interfere with peristalsis Stomach action Circular, longitudinal, and diagonal muscles Timing the release of chyme
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Muscular Action of Digestion
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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
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Muscular Action of Digestion
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Muscular Action of Digestion
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Secretions of Digestion
Five organs Salivary glands, stomach, pancreas, liver, small intestine Secretions Water Enzymes Protein facilitator of chemical reactions Hydrolysis
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Secretions of Digestion
Saliva Moisten food for easy passage Protective role Carbohydrate digestion Gastric juice Protein digestion Mucus pH units
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Secretions of Digestion
Pancreatic juice Released via ducts into duodenum Enzymes act on all three energy nutrients Sodium bicarbonate Bile Liver Gallbladder
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Secretions of Digestion
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The Final Stage Vitamin and mineral absorption Undigested residues
Exercise intestinal muscles Retention of water Colon Intestinal bacteria Recyclable materials Water and dissolved salts
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Absorption Small intestine Majority of absorption Ten feet long
Surface area Absorption techniques Simple diffusion Facilitated diffusion Active transport
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Absorption
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FACILITATED DIFFUSION
Carrier loads nutrient on outside of cell . . . Carrier loads nutrient on outside of cell . . . Outside cell Energy Cell membrane . . . and then releases it on inside of cell. . . . and then releases it on inside of cell. Inside cell Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely. SIMPLE DIFFUSION FACILITATED DIFFUSION Some nutrients (such as the water-soluble 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.) ACTIVE TRANSPORT Some nutrients (such as glucose and amino acids) must be absorbed actively. These nutrients move against a concentration gradient, which requires energy. Figure 3.9: Absorption of Nutrients. Absorption of nutrients into intestinal cells typically occurs by simple diffusion, facilitated diffusion, or active transport. Occasionally, a large molecule is absorbed by endocytosis—a process in which the cell membrane engulfs the molecule, forming a sac that separates from the membrane and moves into the cell. Stepped Art Fig. 3-9, p. 78
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Anatomy of the Absorptive System
Villi Select and regulate nutrients absorbed Microvilli Enzymes and “pumps” Crypts Secretion of intestinal juices Goblet cells Mucus secretion
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Preparing Nutrients for Transport
Transport pathways Bloodstream Water-soluble nutrients and smaller products of fat digestion Liver Lymphatic system Larger fats and fat-soluble vitamins Chylomicrons Bypass liver at first
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The Vascular System Closed system of vessels Blood Heart pump
Delivers oxygen and nutrients Removes carbon dioxide and wastes Blood flow Special routing for digestive system Liver
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The Vascular System
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The Vascular System
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The Lymphatic System One-way route Entry into bloodstream
No pump Circulation between cells Entry into bloodstream Subclavian vein Nutrients in lymphatic vessels Bypass liver at first
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Health and Regulation of GI Tract
Gastrointestinal bacteria – flora Most are not harmful Benefits of gastrointestinal bacteria Factors influencing bacteria presence Diet – probiotics Others Digestion of fibers and complex proteins Vitamin production
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Health and Regulation of GI Tract
Endocrine and nervous systems Homeostatic regulation Hormones and nerve pathways Stimulation and inhibition of digestive secretions Feedback mechanisms Examples GI hormones
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Health and Regulation of GI Tract
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Health and Regulation of GI Tract
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The Digestive System at Its Best
Sensitive and responsive to environment Immunity against intestinal diseases Defense against foreign invaders Health of digestive system Healthy supply of blood Lifestyle factors Types of foods eaten Balance, moderation, adequacy, and variety
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Common Digestive Problems
Highlight 3 Common Digestive Problems
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Choking Food slips into trachea International sign for choking
Cuts off breathing International sign for choking Heimlich maneuver Foods commonly associated with choking Prevention of choking
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Choking
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Choking
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Vomiting and Diarrhea Vomiting Diarrhea Adaptive mechanism of the body
Medical treatment Dehydration and projectile vomiting Diarrhea Symptom of medical conditions & treatments Irritable bowel syndrome (IBS) Colitis Treatment
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Constipation Not a disease Symptoms of constipation Causes Prevention
Lifestyle Side effect of medications Prevention Fiber and water Physical activity
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Belching and Gas Belching Intestinal gas Hiccups Swallowed air
Prevention Intestinal gas Consumption of certain foods Individually determined Hiccups
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Heartburn and “Acid Indigestion”
Gastroesophageal reflux (heartburn) Causes Prevention Indigestion Antacids and acid controllers Damage to esophagus Barrett’s esophagus
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Ulcers Peptic ulcers Causes Ulcer treatment regimen Gastric ulcers
Duodenal ulcers Causes Bacterial infection Anti-inflammatory drugs Excessive gastric acid secretion Ulcer treatment regimen
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