Chapter 21 The Digestive System

Chapter 21 The Digestive System - Ch 21: Digestion Ch...

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Unformatted text preview: Ch 21: Digestion Ch Anatomy of digestive system (review!) 4 major processes of digestive system: 1. Motility 2. Secretion 3. Digestion 3. 4. Absorption 4. Fort Mackinac Mackinac Is, MI GI Anatomy GI Fig 21-1 Motility Motility 2 purposes: Forward movement of food Mechanical mixing GI smooth muscles contract GI spontaneously spontaneously Pacemaker cells, (Interstitial Cells of Pacemaker Cajal), connected by gap junctions, generate slow wave potentials generate APs spread throughout longitudinal APs muscles (gap junctions) ⇒ wave of contraction contraction 2+ Like cardiac muscle, Ca2+ can regulate contraction strength contraction 1. 2. 3. 3. 4. 4. Motility Motility Secretion Secretion Digestion Digestion Absorption Absorption Different Patterns of Contraction Different Tonic Contractions Sustained contraction, usually in the stomach stomach Phasic Contractions Peristaltic contractions progressive waves moving along segments of progressive longitudinal layer → forward propulsion circular layer contracts proximal to bolus circular bolus Especially esophagus Segmental contractions alternate contraction & relaxation lead to mixing A side effect of narcotics Fig 21-4 Secretion Secretion 1. 2. 3. 3. 4. 4. Motility Motility Secretion Secretion Digestion Digestion Absorption Absorption 9 L of fluid pass through the GIT of (only 2 L from food & drink) ⇒ Secretion and Reabsorption important important Ions and water; similar to renal Ions mechanisms mechanisms Saliva Hydrochloric Acid (Parietal Hydrochloric Cells) Cells) Bicarbonate (enzyme necessary ?) Bicarbonate Enzymes (zymogens) Enzymes Mucus (Goblet cells) Mucus (Goblet Bile (bile salts – function?) Bile Net Fluid Balance in GI system Net Fig 21-5 Activation of Zymogens / Proenzymes Proenzymes Regulation of GIT p 689 689 ANS Parasympathetic (R & R) Sympathetic Emotional (cephalic reflexes) E.g., smell of food ENS (Enteric Nervous System) Self-contained (intrinsic) GI peptides can have regulatory GI role as hormones or paracrines role E.g., Gastrin, CCK Table 21-1 Digestion Overview Digestion Mechanical breakdown and mixing aid Mechanical enzymatic breakdown enzymatic Chewing Tonic contractions, esp. stomach Enzymatic breakdown converts Enzymatic macromolecules into absorbable units macromolecules Bile emulsifies fats Optimal pH of enzymes indicates location of Optimal activity activity 1. 2. 3. 3. 4. 4. Motility Secretion Digestion Absorption Absorption Overview Absorption Most nutrient absorption takes place in ? Fats absorbed into lacteals Everything else absorbed into portal vein Alcohol & aspirin across gastric epithelium Additional: H2O, ions & some vitamins O, absorbed in ________________ absorbed Mechanisms analogous to renal absorption 1. 1. 2. 3. 3. 4. 4. Motility Motility Secretion Secretion Digestion Digestion Absorption Absorption CHO Digestion & Absorption Digestion ~50% of calories in average American diet diet Starch (polysaccharide) and sucrose Starch (disaccharide) (disaccharide) Cellulose (roughage) not digestible Enzymes: amylases, disaccharidases amylases, (maltase, sucrase, lactase) (maltase, Absorbed only as monosaccharides (glucose, fructose) (glucose, Small intestine Fig 21-14 Protein Digestion and Absorption Protein Variable digestibility 30-60% of protein not from diet First digestion in Stomach by HCl Proteases secreted as proenzymes Pepsin(-ogen), trypsin, etc. Absorption of single a.a. and di- and Absorption tripeptides tripeptides Specific receptors required for larger Specific chains chains May serve as allergens (Ch 24) May (Ch DDAVP Lipid (fat) Digestion Lipid Mostly triglycerides in diet Cholesterol, Fat-soluble Cholesterol, vitamins, others. vitamins, Combination with bile salts Combination creates an emulsion creates Colipase and lipase allow Colipase formation of small micelles formation Absorption of fat via Absorption diffusion across apical CM diffusion Chylomicrons in the cell are Chylomicrons absorbed into lacteals absorbed See fig 21-19 Other Stuff Other Water soluble vitamins— mediated transport Fat soluble vits. via absorption Water,Ions and Minerals Various locations and methods, Various e.g, diffusion, carrier proteins e.g, Nucleic Acids Colon Cancer Colon 2nd largest cause of cancer deaths Cellulose (indigestible) = fiber, Cellulose roughage roughage Significance of “roughage” in diet?? Olestra Olestra Biotechnology focus p.698 Biotechnology Consumers want fat in their foods → Consumers search for low cal fat substitutes search 1996, Procter & Gamble market Olestra 1996, Olestra = Olean = sucrose polyester (sucrose Olestra molecule + 6-8 FA) molecule Cannot be digested, nor absorbed Unpleasant side effects Absorption of fat sol. vitamins pot. Absorption problem problem Phases of Digestion/Absorption Phases 1. 2. 3. 4. Cephalic Gastric Intestinal Defecation 1. 1. 2. 3. 4. Cephalic Gastric Intestinal Defecation •Anticipation •Salivation •Mastication •Mechanical digestion •Deglutition •Peristalsis in esophagus Reflux Esophagitis = Heartburn = GERD Heartburn Reflux Lower esophageal Lower sphincter dysfunction sphincter Why reflux against gravity? Why See p.700 GERD, cont’d 1. 1. Intrapleural pressure ↓ Intrapleural during inspiration ⇒ Wall of esophagus expands ⇒ Subatmospheric pressure in esophageal lumen sucks acidic stomach contents into esophagus esophagus 1. 1. 2. 3. 4. Cephalic Gastric Intestinal Defecation •Storage •Relaxation or contraction as needed. •Digestion •HCl (Parietal cells) •Pepsin (Chief cells) •Mechanical •Immune Protection •Ingested pathogens •Respiratory mucus 1. 1. 2. 3. 4. Cephalic Gastric Intestinal – Chyme (ingesta) enters small intestine Intestinal Chyme Defecation o Neutralization of HCl o NaHCO3 from pancreas o Running Problem: Peptic Ulcer and antacids, including H2 antagonists and proton pump inhibitors o Pancreatic enzymes o Digest protein, CHO o Bile acids o Emulsion of Fat o Absorption of H2O 1. 2. 3. 4. Cephalic Gastric Intestinal Defecation Bacterial fermentation of CHO and proteins Lactate, some vitamins are digested and/or absorbed Lactate, More H2O absorption More Osmotic diarrhea vs. secretory diarrhea Osmotic Osmotic-solutes prevent H2O reabsorption Lactose intolerance Secretory- bacterial toxins ("flush out' pathogens) Defecation Reflex Fig 21-21 Lactose Intolerance Lactose Clinical focus p. 707 Lactose = glucose + galactose Lactase only found in juvenile Lactase mammals mammals Adaptive (dominant) mutation in Adaptive populations with dairy-based cultures Lactose intolerance in 95% of Native Americans, 90% of Asian Americans 70% of African Americans 50% of Mexican Americans ...
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