Lecture 9 the digestive system

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Lecture 9 the digestive system

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Lecture 9 the digestive system

  1. 1. Copyright 2010, John Wiley & Sons, Inc. Chapter 19 The Digestive System
  2. 2. Copyright 2010, John Wiley & Sons, Inc. Functions of the Digestive System  Ingestion: eating  Secretion: release of water, enzymes, buffers  Mixing and propulsion: movement along GI tract  Digestion: breakdown of foods  Mechanically: by movements of digestive organs  Chemically: by enzymes  Absorption: moving products of digestion into the body  Defecation: dumping waste products
  3. 3. Copyright 2010, John Wiley & Sons, Inc. Organs of the Digestive System  Gastrointestinal (GI) tract  A tube through which foods pass and where digestion and absorption occur.  Includes: mouth, pharynx, esophagus, stomach, small intestine, large intestine  Accessory organs:  Organs that help in digestion but through which food never passes.  Includes: teeth, tongue, salivary glands, liver, gallbladder, and pancreas
  4. 4. Copyright 2010, John Wiley & Sons, Inc. Organs of the Digestive System
  5. 5. Copyright 2010, John Wiley & Sons, Inc. Layers of the Gastrointestinal (GI) Wall  Four layers from lower esophagus to anus 1. Mucosa: epithelium in direct content with food; made of connective tissue, glands, and thin muscularis mucosae 2. Submucosa: connective tissue, blood vessels, lymphatic vessels, and enteric nervous system (ENS)
  6. 6. Copyright 2010, John Wiley & Sons, Inc. Layers of the Gastrointestinal (GI) Wall 3. Muscularis: inner circular layer, outer longitudinal layer  Smooth muscle in most of GI tract  Except skeletal (voluntary muscle) in mouth, pharynx, upper esophagus, and external anal sphincter 4. Serosa: visceral layer of peritoneum  Also forms extensions: greater omentum and mesentery
  7. 7. Copyright 2010, John Wiley & Sons, Inc. Layers of the Gastrointestinal (GI) Wall
  8. 8. Copyright 2010, John Wiley & Sons, Inc. Layers of the Gastrointestinal (GI) Wall
  9. 9. Copyright 2010, John Wiley & Sons, Inc. Layers of the Gastrointestinal (GI) Wall
  10. 10. Copyright 2010, John Wiley & Sons, Inc. Mouth (Oral Cavity)  Formed by  Cheeks and tongue  Hard palate anteriorly, soft palate posteriorly  Uvula  U-shaped extension of soft palate posteriorly  During swallowing, uvula blocks entry of food or drink into nasal cavity  Tongue: muscular accessory organ  Maneuvers food for chewing  Adjusts shape for speech and swallowing  Lingual tonsils at base of tongue
  11. 11. Copyright 2010, John Wiley & Sons, Inc. Salivary Glands  Exocrine glands with ducts that empty into oral cavity  Three pairs of salivary glands  Parotid  Largest; inferior and anterior to ears  Submandibular  In floor of mouth; medial and inferior to mandible  Sublingual  Inferior to tongue and superior to submandibular  Saliva: 99.5% water, salivary amylase, mucus and other solutes  Dissolves food and starts digestion of starches
  12. 12. Copyright 2010, John Wiley & Sons, Inc. Salivary Glands
  13. 13. Copyright 2010, John Wiley & Sons, Inc. Teeth  Accessory organs in bony sockets of mandible and maxilla  Three external regions  Crown: above gums  Root: part(s) embedded in socket  Neck: between crown and root near gum line  Three layers of material  Enamel: hardest substance in body; over crown  Dentin: majority of interior of tooth  Pulp cavity: nerve, blood vessel, and lymphatics
  14. 14. Copyright 2010, John Wiley & Sons, Inc. Teeth
  15. 15. Copyright 2010, John Wiley & Sons, Inc. Teeth  Humans have two sets of teeth  The 20 deciduous teeth are replaced by the permanent teeth between ages 6 and 12 years.  The 32 permanent teeth appear between 6 years and adulthood.  Four types of teeth  Incisors (8): used to cut food  Cuspids (canines) (4): used to tear food  Premolars (8): for crushing and grinding food  Molars (12): used for crushing and grinding food
  16. 16. Copyright 2010, John Wiley & Sons, Inc. Digestion in the Mouth  Mechanical digestion  Chewing mixes food with saliva  Rounds up food into a soft bolus for swallowing  Chemical digestion  Salivary amylase (enzyme) breaks down polysaccharides (starch)  maltose and larger fragments  Continues in the stomach for about an hour until acid inactivates amylase
  17. 17. Copyright 2010, John Wiley & Sons, Inc. Pharynx and Esophagus  Food passages from mouth  stomach  Swallowing: 3 stages  Voluntary stage: bolus of food  oropharynx  Pharyngeal stage: oropharynx  esophagus  Soft palate moves up and epiglottis moves down; prevent food from entering nasopharynx and larynx  Esophageal: food  stomach by peristalsis  Esophageal sphincters:  Upper: controls entry  esophagus  Lower: controls entry  stomach; GERD affects
  18. 18. Copyright 2010, John Wiley & Sons, Inc. Pharynx and Esophagus
  19. 19. Copyright 2010, John Wiley & Sons, Inc. Pharynx and Esophagus
  20. 20. Copyright 2010, John Wiley & Sons, Inc. Stomach  J- shaped enlargement of GI tract  Mixing chamber and holding reservoir  Very elastic/expandable and muscular  Four regions  Cardia: surrounds upper opening  Fundus: superior and to left of cardia  Body: large central portion  Pylorus: lower part leading to pyloric sphincter and duodenum
  21. 21. Copyright 2010, John Wiley & Sons, Inc. Stomach
  22. 22. Copyright 2010, John Wiley & Sons, Inc. Stomach
  23. 23. Copyright 2010, John Wiley & Sons, Inc. Stomach Wall: Four Layers 1. Mucosa  Empty stomach lies in folds called rugae  Epithelium: simple columnar; glands secrete mucus  Gastric glands line gastric pits 2. Secretory cells  Mucous cells  mucus  Parietal cells  HCl and intrinsic factor  These secretions collectively called gastric juice  Intrinsic factor helps with vitamin B12 absorption needed for RBC formation. If missing  anemia  Chief cells  inactive enzyme pepsinogen  G cells secrete gastrin (hormone) into blood
  24. 24. Copyright 2010, John Wiley & Sons, Inc. Stomach Wall: Four Layers 3. Muscularis: Three layers  Outer: longitudinal  Middle: circular  Inner: oblique (extra layer not in other organs) provides for efficient gastric contractions 4. Serous membrane (serosa)  Visceral peritoneum: covers organs  Extensions of serosa  Greater omentum: hangs from curve of stomach  Mesentery: attaches small intestine to posterior wall of abdomen and provides route for vessels
  25. 25. Copyright 2010, John Wiley & Sons, Inc. Stomach Wall: Four Layers
  26. 26. Copyright 2010, John Wiley & Sons, Inc. Digestion and Absorption  Digestion  Mechanical digestion  Stretching of stomach wall  nerve impulses   Secretion + mixing waves   Food mixed with juice  now called chyme  Chemical digestion  Pepsin (pepsinogen + HCl) digests protein  peptides (small chains of amino acids)  Gastric emptying through pyloric sphincter  Carbohydrates fastest, proteins next, fats last  Once in duodenum  feedback inhibition of stomach  Little absorption: water, ions, some drugs
  27. 27. Copyright 2010, John Wiley & Sons, Inc. Pancreas  Location: behind stomach  Produces pancreatic juice in acinar cells  Passes into duodenum via pancreatic duct  Secretions that help digestion  Sodium bicarbonate (NaHCO3): pH 7.1-8.2)  Digestive enzymes: many  Pancreatic lipase: fat-digesting  Pancreatic amylase: starch-digesting  Proteases: made in inactivated form  Activated by enterokinase from small intestine  Chymotrypsinogen, trypsinogen, carboxypeptidase  RNAase and DNAase
  28. 28. Copyright 2010, John Wiley & Sons, Inc. Liver and Gallbladder  Weighs 1.4 kg (3 lb): 2nd largest organ in the body; large right lobe + 3 smaller parts  In right upper quadrant, below diaphragm  Bile production and pathway  Hepatocytes (liver cells) make bile   Bile canaliculi  bile ducts  hepatic duct   Gallbladder (green, pear-shaped organ that stores bile)   Cystic duct  common bile duct  duodenum
  29. 29. Copyright 2010, John Wiley & Sons, Inc. Liver and Gall Bladder  Functional unit is lobule  Consists of hepatocytes in rows that radiate around central vein  Sinusoids (permeable capillaries with phagocytic [Kuppfer] cells) are between cells  Blood reaches liver lobules from  Hepatic artery (branch of celiac): blood high in O2  Hepatic portal vein (formed by veins from digestive organs and spleen): blood low in O2 but rich in nutrients from digestive organs
  30. 30. Copyright 2010, John Wiley & Sons, Inc. Bile  Functions of bile  Emulsification: breaking apart clusters of fats so they are more digestible  Absorption of fats  Formation and recycling of bile  Bilirubin from heme when RBCs broken down  Bile is digested  stercobilin: gives feces brown color  Bile salts reabsorbed into blood in small intestine (ileum)  portal vein  liver  Gallstones may form from bile  Obstruct bile ducts from gallbladder  pain
  31. 31. Copyright 2010, John Wiley & Sons, Inc. Liver, Gallbladder, Duodenum
  32. 32. Copyright 2010, John Wiley & Sons, Inc. Liver
  33. 33. Copyright 2010, John Wiley & Sons, Inc. Liver
  34. 34. Copyright 2010, John Wiley & Sons, Inc. Liver Functions 1. Carbohydrate metabolism  Polysaccharide stored in liver as glycogen  Converts glycogen, fructose, galactose, lactic acid, amino acids  glucose to blood glucose 2. Lipid metabolism  Produces cholesterol, triglycerides; makes bile  Makes lipoproteins for lipid transport 3. Protein metabolism  Remove NH2 from amino acids  ammonia (NH3)  urea  to kidneys (urine)  Synthesize most plasma proteins: albumin
  35. 35. Copyright 2010, John Wiley & Sons, Inc. Liver Functions 4. Removes many harmful substances from blood  Detoxifies alcohol  Inactivates steroid and thyroid hormones  Eliminates some drugs (like penicillin) into bile 5. Excretion of bilirubin  From heme (in RBCs) to bile  feces 6. Stores fat-soluble vitamins (ADEK) and minerals (Fe, Cu) 7. Activates vitamin D
  36. 36. Copyright 2010, John Wiley & Sons, Inc. Small Intestine  Length  10 feet long in living person  Extends from pylorus of stomach to cecum of large intestine  Three major regions: duodenum, jejunum, ileum  Functions  Site of most of digestion  Essentially all nutrient absorption occurs here  Ends in ileocecal sphincter (in RLQ)
  37. 37. Copyright 2010, John Wiley & Sons, Inc. Small Intestine
  38. 38. Copyright 2010, John Wiley & Sons, Inc. Small Intestine
  39. 39. Copyright 2010, John Wiley & Sons, Inc. Intestinal Wall Structure  Same 4 layers but with modifications  Epithelium in mucosa: simple columnar  Absorptive cells with microvilli  Goblet cells: secrete mucus  Intestinal glands secrete  Enzymes that complete digestion  Secretin, cholecystokinin (CCK), glucose- dependent insulinotropic peptide (GIP)  Lymphatic tissue within wall: defense
  40. 40. Copyright 2010, John Wiley & Sons, Inc. Intestinal Wall Structure  Submucosa has duodenal glands   Alkaline mucus  helps neutralize stomach acid  Circular folds  In mucosa and submucosa; increase surface area  Villi: fingerlike projections of mucosa  Increase absorptive surface area  Microvilli on absorptive cells further enhance absorption  Contain vessels that absorb nutrients:  Arteriole, capillary, venule  Lacteal (lymph capillary) for lipid absorption
  41. 41. Copyright 2010, John Wiley & Sons, Inc. Intestinal Wall Structure
  42. 42. Copyright 2010, John Wiley & Sons, Inc. Digestion in Small Intestine  Mechanical digestion  Segmentation activity: for mixing  Peristalsis for movement of intestinal contents after most absorption completed: slow waves  Chemical digestion: 2 L/d of secretions  Alkaline chyme due to bicarbonate  From pancreas and alkaline mucus from small intestine  Enzymes produced by cells on villi  Peptidases: breaks small peptides  Disaccharidases: sucrase, lactase, and galactase
  43. 43. Copyright 2010, John Wiley & Sons, Inc. Absorption in the Small Intestine  Chyme enters small intestine carrying partially digested carbohydrates and proteins  Intestinal juice (composed of bile, pancreatic juice, intestinal juice) completes digestion  90% of absorption of products of digestion occurs in the small intestine  Monosaccharides; amino acids  Fatty acids and monoglycerides  Phosphate sugar, and bases of DNA, RNA
  44. 44. Copyright 2010, John Wiley & Sons, Inc. Summary: Carbohydrate Digestion  Amylases (salivary and pancreatic):  Starch and dextrin  maltose  Disaccharidases (from small intestine):  Maltose: maltose  glucose + glucose  Lactase: lactose  glucose + galactose  Sucrase: sucrose  glucose + fructose
  45. 45. Copyright 2010, John Wiley & Sons, Inc. Protein and Fat Digestion  Pepsin, trypsin, chymotrypsin, and carboxypeptidase  Proteins small peptides  Peptidases at surface:  Peptides  amino acids, dipeptides, and tri-peptides  Lipase (pancreatic)  Triglyceridesfatty acids + monoglycerides
  46. 46. Copyright 2010, John Wiley & Sons, Inc. Absorption of Products of Digestion  By diffusion, facilitated diffusion, osmosis and active transport  Carbohydrates monosaccharides  Via portal system (blood) to liver  Proteins (jejunum + ileum)  amino acids  Via portal system (blood) to liver  Lipids   Short-chained fatty acids or monoglycerides or  blood in villi  Larger lipids coated by proteins in chlyomicrons  lacteals  lymphatics (lymph)  then blood
  47. 47. Copyright 2010, John Wiley & Sons, Inc. Absorption of Products of Digestion  Water and salt  Primarily osmotic movement that accompanies other nutrients  Vitamins  Fat-soluble (A, D, E, K) absorbed with fat  Water-soluble (B’s, C) with simple diffusion  B12  Combines with intrinsic factor for transport through duodenum and jejunum  Finally can be absorbed by active transport in ileum
  48. 48. Copyright 2010, John Wiley & Sons, Inc. Absorption of Products of Digestion
  49. 49. Copyright 2010, John Wiley & Sons, Inc. Absorption of Products of Digestion
  50. 50. Copyright 2010, John Wiley & Sons, Inc. Large Intestine  Structure: 4 regions  Cecum  Ileocecal sphincter  Appendix attached  Colon: ascending, transverse, descending and sigmoid  Rectum  Anal canal with sphincters  Wall: standard 4 layers  Mucosa: goblet cells secrete mucus  Muscularis: incomplete longitudinal layer
  51. 51. Copyright 2010, John Wiley & Sons, Inc. Large Intestine
  52. 52. Copyright 2010, John Wiley & Sons, Inc. Large Intestine
  53. 53. Copyright 2010, John Wiley & Sons, Inc. Large Intestine
  54. 54. Copyright 2010, John Wiley & Sons, Inc. Digestion and Absorption  Ileocecal sphincter limits rate of emptying of ileum  Slow peristalsis  Mass peristalsis  Triggered by presence of food in stomach  Wastes move from mid-colon  rectum  Bacterial digestion  Produce some B-vitamins + vitamin K  Produce gases: flatus  Colon absorbs salt + water
  55. 55. Copyright 2010, John Wiley & Sons, Inc. Defecation Reflex  Stretch of rectum wall  neural reflex  contraction of longitudinal muscle  Combined pressure + parasympathetic activity relaxes internal anal sphincter  External anal sphincter is voluntary  Contraction of diaphragm and abdominal muscles aid defecation
  56. 56. Copyright 2010, John Wiley & Sons, Inc. Control: Phases of Digestion  Rule: activate forward and inhibit behind  Three phases: cephalic, gastric, intestinal 1. Cephalic: smell, sight, thought of food   Cranial nerves VII + IX stimulate salivary glands  Cranial nerve X (vagus) stimulates gastric glands 2. Gastric: stretching, pH of stomach   Gastrin activates stomach and relaxes pyloric sphincter 3. Intestinal phase: intestinal hormones play key roles
  57. 57. Copyright 2010, John Wiley & Sons, Inc. Control: Phases of Digestion  Secretin  Released when acidic chyme enters intestine  Stimulates release of pancreatic juice high in bicarbonate to buffer acidic chyme from stomach  Cholecystokinin (CCK)  Released when chyme rich in amino acids and fatty acids enters intestine  Stimulates release of pancreatic juice high in digestive enzymes  Decreases gastric motility and secretion  Causes gallbladder to contract and eject bile
  58. 58. Copyright 2010, John Wiley & Sons, Inc. Aging  Decreased GI secretion, motility, strength of responses  Loss of taste, increased risk for periodontal disease, difficulty swallowing, hiatal hernia, gastritis, peptic ulcer disease  Increased risk for gallbladder problems, cirrhosis of liver, pancreatitis, constipation, hemorrhoids, diverticulitis
  59. 59. Copyright 2010, John Wiley & Sons, Inc. End of Chapter 19  Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.

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