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運動營養學專題研究 Sport Nutrition Chapter 5 Gastric emptying, digestion, and absorption 張振崗 教授 Jeukendrup A, Gleeson M. Sport nutrition: an introduction to energy production and performance, 2nd Ed. Human Kinetics, 2010 1 Chapter 16 The Digestive System PowerPoint® Lecture Slides prepared by Jason LaPres Lone Star College - North Harris Copyright © 2010 Pearson Education, Inc. 2 3 Digestive Tract Digestive tract also called gastrointestinal (GI) tract or alimentary canal Is a muscular tube Extends from oral cavity to anus: Passes through pharynx, esophagus, stomach, and small and large intestines 4 Accessory Organs Figure 16-1 5 Digestive Tract Figure 16-1 6 Functions of the Digestive System -1 Ingestion Occurs when materials enter digestive tract via the mouth Mechanical processing Crushing and shearing Makes materials easier to propel along digestive tract Digestion The chemical breakdown of food into small organic fragments for absorption by digestive epithelium 7 Functions of the Digestive System -2 Secretion Is the release of water, acids, enzymes, buffers, and salts By epithelium of digestive tract, and glandular organs Absorption Movement of organic substrates, electrolytes, vitamins, and water Across digestive epithelium Into interstitial fluid of digestive tract Excretion 排遺 Removal of waste products from body fluids 8 Digestive Tract Lining of the digestive tract protects surrounding tissues against Corrosive effects of digestive acids and enzymes Mechanical stresses, such as abrasion Bacteria either ingested with food or that reside in digestive tract Major layers of the digestive tract Mucosa Submucosa Muscularis externa Serosa 9 The Structure of the Digestive Tract Figure 16-2 10 Segments of the Intestine Figure 16-10 11 The Intestinal Wall Histology of the Small Intestine Plicae circulares 環行皺襞 : Transverse folds in intestinal lining Are permanent features: Intestinal villi: A series of fingerlike projections: in mucosa of small intestine Covered by simple columnar epithelium: do not disappear when small intestine fills covered with microvilli ~3300 cm2 absorptive area 12 The Intestinal Wall Figure 16-11a 13 The Intestinal Wall Figure 16-11b 14 The Intestinal Wall Figure 16-11c 15 Daily secretion of intestinal juices Saliva: 1000 ml Gastric secretions: 1500 ml Pancreatic secretion: 1000 ml Bile: 1000 ml Small intestine: 2000 ml Large intestine: 200 ml Total: 6700 ml Mostly reabsorbed 16 17 18 19 20 21 Absorption of water 99% water absorption in small intestine, by simple diffusion Water flow toward compartment with lower water concentration (higher solute concentration) Osmole: number of solute particles mOsm/kg (osmolality), mOsm/L (osmolarity 滲透壓) ~290 mOsm/L for most body fluids If ingested high osmolarity, water move into gut lumen 22 Osmosis 滲透 23 24 Absorption of vitamins Mostly in small intestine via diffusion Digestion free vitamins from coenzymes Fat-soluble vitamins absorbed along with FA Water-soluble vitamins Incorporated into chylomicrons Transported through lymphatic system Not retained to any great extent in body Additional vit K, B12, thiamine, riboflavin can be formed by bacteria in colon 25 26 Absorption of minerals Minerals not very well absorbed in human intestine Absorption rate, retention rate depend on intake, storage, and requirement 27 28 29 Regulation of gastric emptying Gastric motility and secretion mostly automatic Stomach signals: usually positive feedback Nervous signals from stretching and extension of stomach wall, relax pyloric sphincter Release of gastrin Intestinal signals: usually negative feedback Duodenum contains receptors for pH, distension of duodenum, osmolarity 30 Factors for gastric emptying Fluid volume in stomach, exponential Not affected by exercise up to 80% VO2max High osmolarity reduce gastric emptying Short- or long-term high intensity exercise reduce gastric emptying Not important in 200-400 mOsm/L, typical for most sport drinks High energy density reduce gastric emptying Temperature of food usually no effect Psychological stress reduce gastric emptying 31 Regulation of gastric emptying 32 Rate of gastric emptying