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IB Biology Digestion

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IB Biology Digestion

  1. 1. IB Biology Digestive System
  2. 2. Digesting large molecule <ul><li>• Most food molecules are large polymers and insoluble </li></ul><ul><li>• They must first be digested to smaller soluble molecules before they can be absorbed into the blood </li></ul>
  3. 3. Enzymes and digestion <ul><li>• Enzymes are biological catalysts that increase the rate of reaction </li></ul><ul><li>• Digestive enzymes are secreted into the lumen of the gut </li></ul><ul><li>• Digestive enzyme increase the rate of reaction of the hydrolysis of insoluble food molecules to soluble end products </li></ul><ul><li>• Digestive enzymes increase the rate of reaction at body temperature </li></ul>
  4. 4. Example 1: Pancreatic Amylase <ul><li>Condition </li></ul><ul><li>• Source the Pancreas </li></ul><ul><li>• Optimal pH 7.5-7.8 </li></ul><ul><li>• Substrate is starch (amylose) </li></ul><ul><li>• End product is the disaccharide maltose </li></ul><ul><li>• Action: hydrolysis of 1-4 glycosidic bonds </li></ul>
  5. 5. Example 2: Pepsin is a protease enzyme <ul><li>Condition </li></ul><ul><li>• Source is the stomach </li></ul><ul><li>• Optimal pH is 2 </li></ul><ul><li>• Substrate is a polypeptide chains of amino acids </li></ul><ul><li>• End product is small polypeptides </li></ul><ul><li>• Action is the hydrolysis of peptide bonds within the polypeptide chain. </li></ul>
  6. 6. Example3: Pancreatic Lipases <ul><li>• Source is the pancreas </li></ul><ul><li>• The optimal pH is 7.2 </li></ul><ul><li>• The substrate is a triglyceride lipid </li></ul><ul><li>• The product is glycerol and fatty acid chains </li></ul><ul><li>• The action of pancreatic amylases also requires the presence of bile salts that emulsify the lipid . </li></ul><ul><li>This emulsification has two effects: </li></ul><ul><li>1.Increases the surface area of the lipid for the digestion of fat </li></ul><ul><li>2.Exposes the glycerol 'head' structure to the enzyme </li></ul><ul><li>• Action: hydrolysis of ester bonds between the glycerol molecules and the fatty acid chains. </li></ul>
  7. 7. Example3: Pancreatic Lipases
  8. 8. Figure 41.13 The human digestive system
  9. 9. <ul><li>Digestion begins in the oral cavity (mouth). </li></ul><ul><li>Saliva begins the chemical digestion of food. Saliva contains the protein mucin to lubricate the food for swallowing. </li></ul><ul><li>Amylase breaks down starch and glycogen. </li></ul><ul><li>Food is shaped into a ball (bolus) and is then swallowed. </li></ul>
  10. 10. <ul><li>The food then proceeds down through the esophagus through peristalsis : an involuntary contraction of smooth muscle tissue. </li></ul>
  11. 11. Figure 41.14 From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 1)
  12. 12. Figure 41.14 From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 2)
  13. 13. Figure 41.14 From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 3)
  14. 14. Pharynx (throat): <ul><li>Is where the esophagus and the windpipe meet. </li></ul><ul><li>When food is swallowed, the epiglottis closes the passage to the windpipe. </li></ul><ul><li>The epiglottis is a flap made of cartilage that cover the glottis (opening to the windpipe). </li></ul>
  15. 15. Esophagus: <ul><li>Conducts food from the pharynx to the stomach. </li></ul><ul><li>The mouth, pharynx and esophagus are responsible for carbohydrate digestion. </li></ul>
  16. 16. Stomach: <ul><li>The opening to the esophagus is called the cardiac sphincter . </li></ul><ul><li>The opening end of the stomach to the small intestine is called the pyloric sphincter . </li></ul><ul><li>The stomach produces gastric juice. </li></ul><ul><li>If the cardiac sphincter opens when it shouldn’t, you get acid reflux or heartburn. </li></ul>
  17. 17. Gastric Juice: <ul><li>Has a pH of ~ 2. </li></ul><ul><li>Contains pepsin that breaks down proteins. </li></ul><ul><li>A coating of mucus helps protect the stomach wall. </li></ul><ul><li>The stomach epithelium must be regenerated every 3 days. </li></ul><ul><li>Ulcers are generated when the stomach wall is being degraded. </li></ul>
  18. 18. <ul><li>After chemical digestion in the stomach, the food has been turned into a nutrient broth called chyme . </li></ul><ul><li>It takes 2to 6 hours for the stomach to empty. </li></ul>
  19. 20. Structure: Small Intestine <ul><li>In the small intestine digestion is completed. The products of digestion are absorbed into the blood stream. </li></ul>
  20. 21. Structure: Small Intestine <ul><li>Villus which increase the surface area for absorption of the products of digestion </li></ul><ul><li>(b) Microvilli border of the epithelial cell increases the surface are for absorption. </li></ul><ul><li>(c) Lacteals are connect to the lymphatic system for the transport of lipids. </li></ul><ul><li>(d) In the wall of the small intestine are the blood vessels to transport absorbed products to the general circulation, There are also the muscle to maintain peristalsis </li></ul>
  21. 22. Small intestine: <ul><li>After leaving the stomach, food enters the small intestine (SI). </li></ul><ul><li>The SI is the major organ of digestion and absorption. </li></ul><ul><li>The first part of the SI is called the duodenum . </li></ul>
  22. 23. Figure 41.16 The duodenum
  23. 24. Pancreas: <ul><li>Produces hydrolytic enzymes and an alkaline solution made of bicarbonate. </li></ul><ul><li>The bicarbonate acts as a buffer to help neutralize the acidic chyme. </li></ul>
  24. 25. Liver: <ul><li>In digestion, the liver produces bile. </li></ul><ul><li>Bile contains no digestive enzymes, but contains salts which acts as a detergent and helps in the absorption of fats. </li></ul><ul><li>Bile also contains some wastes of the liver (red blood cell destruction). </li></ul>
  25. 26. SI: <ul><li>Breaks down and absorbs fats with the help of bile from the liver. </li></ul><ul><li>Nearly all fate that enters the SI is completely undigested. </li></ul><ul><li>The SI also produces lipase to aid in lipid digestion. </li></ul>
  26. 27. Figure 41.17 Enzymatic digestion in the human digestive system
  27. 29. Large Intestine (LI): <ul><li>Is also called the colon . </li></ul><ul><li>It is connected to the SI with a sphincter. </li></ul><ul><li>The cecum is the pouch located in the LI near the SI. </li></ul><ul><li>The appendix is a finger-like extension of the cecum. </li></ul>
  28. 30. LI: <ul><li>The primary job of the LI is to reabsorb water. </li></ul><ul><li>Together, the SI and the LI reabsorb ~ 90% of the water that was used for digestion. </li></ul><ul><li>Wastes become more solid as they move through the LI through peristalsis and results in feces . </li></ul>
  29. 31. LI: <ul><li>The end of the LI (colon) is called the rectum . </li></ul><ul><li>Between the rectum and the anus there are 2 sphincters; one involuntary and the other voluntary. </li></ul>
  30. 32. Absorption and assimilation <ul><li>Insoluble food molecules are digested to soluble </li></ul><ul><li>products in the lumen of the gut. </li></ul><ul><li>Absorption: </li></ul><ul><li>1.The soluble products are first taken up by various mechanisms into the epithelial cells that line the gut. </li></ul><ul><li>2.These epithelial cells then load the various absorbed molecules into the blood stream. </li></ul><ul><li>Assimilation: </li></ul><ul><li>1.The soluble products of digestion are then transported to the various tissues by the circulatory system. </li></ul><ul><li>2.The cells of the tissues then absorb the molecules for use within this tissues </li></ul>
  31. 33. Absorption and assimilation
  32. 34. Vertebrate Digestive Systems: <ul><li>Vary depending on the diet of the organism. </li></ul><ul><li>The oral cavity contains incisors, canines and molar teeth. </li></ul><ul><li>The law is designed for the diet. </li></ul><ul><li>Herbivores have a very long cecum and LI. </li></ul><ul><li>Carnivores and omnivores have a small cecum and a shorter LI. </li></ul>
  33. 35. Figure 41.21 The digestive tracts of a carnivore (coyote) and a herbivore (koala) compared

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