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Chapter 21a

Chapter 21a. The Digestive System. About this Chapter. Digestion function and processes Anatomy of the digestive system Motility Secretion Regulation of GI function Digestion and absorption. About this Chapter. The cephalic phase The gastric phase The intestinal phase

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Chapter 21a

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  1. Chapter 21a The Digestive System

  2. About this Chapter • Digestion function and processes • Anatomy of the digestive system • Motility • Secretion • Regulation of GI function • Digestion and absorption

  3. About this Chapter • The cephalic phase • The gastric phase • The intestinal phase • Immune functions of the GI tract

  4. Activities of the Digestive System Note: Which of these activities occur at each region of the GI tract. Explain how these activities occur, control (hormones or neural), enzymes and structural mechanisms, no need to name the transporters. • Ingestion • Digestion • Mechanical • Chemical / Secretion • Motility • Peristaltic • Segmentation • Absorption • Immunity • Elimination

  5. Fluid input intodigestive system Ingestion 2.0 L food anddrink Secretion 1.5 L saliva(salivaryglands) Fluid removedfrom digestivesystem 0.5 L bile(liver) 2.0 L gastricsecretions Absorption 7.5 L from smallintestine 1.5 L pancreaticsecretions 1.4 L from largeintestine 1.5 L intestinalsecretions Excretion 0.1 L in feces 9.0 L removedfrom lumen 9.0 L Total inputinto lumen Digestive Function and Processes • The volume of fluid entering the GI tract must equal the volume leaving 9 liters per day Figure 21-1

  6. Four Basic Processes of the Digestive System Food SECRETION DIGESTION ABSORPTION MOTILITY Lumen of digestive tract Wall Interstitialfluid Blood Figure 21-2

  7. Digestive System Anatomy • Trace through digestive system, not specific regions in addition to major parts. Also note accessory structures. • Most simply: • Oral cavity  pharynx esophagus  stomach  small intestine  large intestine rectum • Accessory • Salivary glands • Pancreas • Liver and gall bladder ANATOMY SUMMARY THE DIGESTIVE SYSTEM Oral cavity Salivaryglands Esophagus Gallbladder Liver Pancreas Stomach Smallintestine Largeintestine Rectum (a) Figure 21-3a

  8. Digestive System Anatomy • Stomach • Fundusbody antrum (pylorus) • Pyloric valve • Small intestine • Duodenum  jejunum  ileum • Accessory organs: pancreas and liver • Large intestine: colon (ascending, transverse, descending and sigmoid colons) and rectum • Anus

  9. Digestive System Anatomy • A closer look at the structure of the stomach and small intestine STRUCTURE OF THE STOMACH AND INTESTINE ANATOMY SUMMARY Esophagus Fundus Diaphragm THE DIGESTIVE SYSTEM Body Antrum Oral cavity Salivaryglands Esophagus Pylorus Mesentery Mucosa Rugae: Surface foldingincreases area Submucosa (b) The stomach Gallbladder Liver Pancreas Stomach Plica Smallintestine Circularmuscle Largeintestine Longitudinalmuscle Submucosal glands Rectum Serosa Villi (a) (d) Structure of the small intestine Figure 21-3a–b, d

  10. Digestive System Anatomy • Layers: same throughout, but modified for different functions • Mucosa • Created from • Epithelial cells • Lamina propria • Muscularismucosae • Modifications increase surface area • Rugae / Plica and villi / crypts • Submucosa • Muscularisexterna • Serosa

  11. Digestive System Anatomy SECTIONAL VIEW OF THE STOMACH Opening togastric gland Mucosa Epithelium Lymph vessel Lamina propria Arteryand vein Muscularis mucosae Submucosa Oblique muscle Muscularisexterna Circular muscle Myentericplexus Longitudinalmuscle Serosa (c) Figure 21-3c

  12. Digestive System Anatomy SECTIONAL VIEW OF THE SMALL INTESTINE Villi Crypt Mucosa Lymphvessel Muscularismucosae Submucosalplexus Submucosa Circularmuscle Myentericplexus Muscularisexterna Longitudinalmuscle Serosa Submucosalartery and vein Peyer’s patch (e) Figure 21-3e

  13. Digestive System Anatomy PLAY Interactive Physiology® Animation:Digestive System: Anatomy Review: Overall Function of the GI System

  14. Motility • Tonic contractions • Sustained • Occur in smooth muscle sphincters and stomach • Keep bolus from moving backwards • Phasic contractions • Last a few seconds • Peristalsis moves bolus forward • Segmentation mixes

  15. Contractions in the GI Tract • Peristalsis promotes forward movement Figure 21-5a

  16. Motility • Segemental contractions promote mixing PLAY Interactive Physiology® Animation:Digestive System: Motility Figure 21-5b

  17. Secretion • 9 liters / day 7 of which from secretions • Parietal cells secrete hydrochloric acid into the lumen of the stomach. Other sources include: duodenum / pancreas / salivary glands Lumen ofstomach Interstitialfluid Capillary H2O H+ H+ + OH– ATP CA K+ K+ HCO3– HCO3– CO2 Cl– Cl– Cl– Cl– Parietal cell CA = Carbonic anhydrase Figure 21-6

  18. Secretion • Anatomy of the exocrine and endocrine pancreas acini and islets Duct cellssecrete NaHCO3 Pancreatic islet cells Lumen Acinar cells Pancreaticacini Figure 21-7

  19. Secretion • Bicarbonate secretion in the pancreas and duodenum Lumen ofpancreas orintestine Pancreatic duct cellor duodenal cell Interstitialfluid Capillary H2O + CO2 CO2 CA HCO3– HCO3– + H+ Na+ Cl– Na+ Cl– ATP K+ CFTRchannel Na+ 2 Cl– K+ K+ H2O, Na+ Figure 21-8

  20. Secretion • Cl– secretion by intestinal and colonic crypt cells 1 1 Na+, K+ and Cl– enter bycotransport. Lumen Interstitialfluid 2 Cl– enters lumen throughCFTR channel. K+ 1 2 K+ 3 3 Cl– 2 Cl– Cl– Na+ is reabsorbed. Na+ CFTR channel Na+ 4 Negative Cl– in lumen attractsNa+ by paracellular pathway.Water follows. ATP 3 K+ 4 Na+,H2O Na+,H2O Figure 21-9

  21. Secretion • Digestive enzymes secreted into mouth, stomach and intestine • Mucous cells in stomach and goblet cells in intestine • Saliva is an exocrine secretion • Liver secretes bile PLAY Interactive Physiology® Animation:Digestive System: Secretion

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