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  1. 1. Unit C1-2: Human Biology (Digestive System) <ul><li>Students who have fully met the prescribed learning outcomes (PLO’s) are able to: </li></ul><ul><li>C1. Analyze the functional inter-relationships of the structures of the digestive system. </li></ul><ul><ul><li>Identify and give a function for each of the following: </li></ul></ul><ul><li>-mouth -duodenum </li></ul><ul><li> -tongue -liver </li></ul><ul><li> -teeth -gall bladder </li></ul><ul><li> -salivary glands -pancreas </li></ul><ul><li> -pharynx -small intestine </li></ul><ul><li> -epiglottis -large intestine (colon) </li></ul><ul><li> -esophagus -appendix </li></ul><ul><li> -cardiac sphincter -rectum </li></ul><ul><li> -stomach -anus </li></ul><ul><li> -pyloric sphincter </li></ul>
  2. 2. Digestion PLO’s <ul><ul><li>Describe swallowing and peristalsis. </li></ul></ul><ul><ul><li>Identify the pancreas as the source gland for insulin, and describe the function of insulin in maintaining blood sugar levels. </li></ul></ul><ul><ul><li>List at least six major functions of the liver. </li></ul></ul><ul><ul><li>Explain the role of bile in the emulsification of fats. </li></ul></ul>
  3. 3. Digestion PLO’s <ul><ul><li>Describe how the small intestine is specialized for chemical and physical digestion and absorption. </li></ul></ul><ul><ul><li>Describe the structure of the villus, including microvilli, and explain the functions of the capillaries and lacteals within it. </li></ul></ul><ul><ul><li>Describe the functions of anaerobic bacteria in the colon. </li></ul></ul><ul><ul><li>Demonstrate the correct use of the dissection microscope to examine the various structures of the digestive system . </li></ul></ul>
  4. 4. Digestion PLO’s (Last set!) <ul><ul><li>Describe the role of sodium bicarbonate in pancreatic juice. </li></ul></ul><ul><ul><li>Describe the role of hydrochloric acid (HCl) in gastric juice. </li></ul></ul><ul><ul><li>Describe the role of mucus in gastric juice. </li></ul></ul><ul><ul><li>Describe the importance of the pH level in various regions of the digestive tract. </li></ul></ul>
  5. 5. C1 – Organs and Their Functions :
  6. 6. First off…..the MOUTH!!
  7. 7. Mouth…where it all begins <ul><li>Receives food to be broken down physically (teeth)and chemically . </li></ul><ul><li>Location of starch digestion/first place of chemical digestion of starch. </li></ul><ul><li>Saliva in mouth provides optimal pH 7 for salivary amylase. </li></ul>
  8. 8. Tongue <ul><li>Forms chewed food into a bolus (ball of food) before swallowing. </li></ul><ul><li>Initiates swallowing. </li></ul>
  9. 9. Teeth! Chomp chomp…. <ul><li>Mechanical/physical breakdown of food (mastication). </li></ul>
  10. 10. Salivary Glands <ul><li>Three pairs of glands that secrete saliva into the mouth via ducts. </li></ul><ul><li>Produces saliva containing water, mucus , salivary amylase and buffers which, lubricate food, and breakdown starch into maltose. (It also contains the enzyme, lysozyme that lyses oral bacteria). </li></ul>
  11. 11. Salivary Glands
  12. 12. Pharynx <ul><li>A region between the mouth, esophagus, and trachea. </li></ul><ul><li>Passageway for food, water, air, and for the reflex action of swallowing as it enters the esophagus. </li></ul>
  13. 13. Epiglottis…so you don’t choke! <ul><li>A flap of tissue that covers the glottis (opening of the trachea). </li></ul><ul><li>Prevents food from entering the trachea when swallowing. </li></ul>
  14. 14. Esophagus <ul><li>Transfers the bolus from the mouth to the stomach by peristalsis (rhythmic smooth muscle contractions). </li></ul><ul><li>Secretes mucus for lubrication </li></ul>
  15. 15. Cardiac Sphincter <ul><li>Circular muscle at the junction of the esophagus and stomach. </li></ul><ul><li>Relaxation of sphincter allows bolus to enter stomach and contraction prevents stomach chyme from re-entering the esophagus. </li></ul>
  16. 16. Stomach <ul><li>J-shaped muscular and glandular organ on the left side of body below the diaphragm. </li></ul><ul><li>Stomach wall contains deep folds ( rugae ) which provide a greater surface area for food and fluids. </li></ul><ul><li>Storage of food </li></ul>
  17. 17. Stomach continued <ul><li>Mechanical churning of food into chyme by smooth muscle fibres. </li></ul><ul><li>Secrete mucus for protection and lubrication by goblet cells. </li></ul><ul><li>Secretes HCl and pepsinogen (inactive form of pepsin ) by gastric glands. </li></ul><ul><li>Secretes gastric juice produced by gastric glands containing H 2 O, HCl, pepsinogen (pepsin), and mucus. HCl provides optimal pH 2-3 for pepsin. </li></ul>
  18. 18. Stomach <ul><li>First place of chemical digestion of proteins . </li></ul><ul><li>Secretes gastrin (hormone), which releases more gastric juice from gastric glands. </li></ul>
  19. 19. Pyloric Sphincter <ul><li>A circular ring of muscle at the junction of the stomach and duodenum. </li></ul><ul><li>Relaxation of the sphincter allows acid chyme to enter the duodenum, </li></ul><ul><ul><li>i.e. controls the amount of chyme entering the duodenum and contraction keeps chyme within the stomach. </li></ul></ul>
  20. 20. Duodenum <ul><li>First 30cm of the small intestine. </li></ul><ul><li>Receives acid chyme from stomach, pancreatic juice from pancreas, and bile from gall bladder; peristalsis occurs here. </li></ul><ul><li>Bile begins its first emulsification of lipids here, i.e. lipids physically broken down into lipid droplets. </li></ul>
  21. 21. Duodenum
  22. 22. Duodenum Continued <ul><li>Majority of chemical digestion (see below) and the first neutralization (via NaHCO 3 ) of acidic chyme occur here. NaHCO 3 provides optimal pH 8-9 for pancreatic amylase, lipase, trypsin, intestinal & pancreatic nuclease, peptidase and maltase. </li></ul>
  23. 23. Enzymes at work <ul><ul><ul><ul><ul><li>H 2 O </li></ul></ul></ul></ul></ul><ul><li>starch maltose </li></ul><ul><li>pancreatic amylases </li></ul><ul><li>H 2 O </li></ul><ul><li>maltose glucose </li></ul><ul><li>maltase </li></ul><ul><li> </li></ul><ul><li>H 2 O </li></ul><ul><li>proteins peptides </li></ul><ul><li> trypsin </li></ul>
  24. 24. More enzymes <ul><li>H2O </li></ul><ul><li>peptides amino acids </li></ul><ul><li>peptidase </li></ul><ul><li>H2O </li></ul><ul><li>nucleic acids nucleotides </li></ul><ul><li>pancreatic & intestinal nucleases </li></ul><ul><li>H2O </li></ul><ul><li>lipid droplets glycerol & </li></ul><ul><li>lipase fatty acids </li></ul>
  25. 25. Liver <ul><li>Refer to major liver functions for specifics . </li></ul><ul><li>Accessory organ for digestion consisting of four lobes, located under the diaphragm. </li></ul><ul><li>Approximately 1.5kg in weight. </li></ul><ul><li>Highly vascularized. </li></ul><ul><li>Produces bile (bile salts) necessary for emulsifying lipids (thus increasing surface area for chemical digestion by lip ase ). </li></ul>
  26. 26. Gall Bladder <ul><li>Accessory organ for digestion. </li></ul><ul><li>Pear-shaped sac located in a depression on the underside of the liver. </li></ul><ul><li>Stores and concentrates bile from the liver and carries it to the duodenum via the bile duct. </li></ul>
  27. 27. Pancreas <ul><li>Refer to function of insulin for specifics . </li></ul><ul><li>Accessory organ for digestion. </li></ul><ul><li>Oblong gland, approximately 12.5cm, which lies behind the stomach and made up of clusters of glandular cells. </li></ul>
  28. 28. Pancreas <ul><li>Secretes pancreatic juice containing H 2 O, NaHCO 3 , pancreatic amylase , lipase , trypsin and pancreatic nuclease . </li></ul><ul><li>Secretes pancreatic juice for further digestion of starch, lipid droplets, proteins and nucleic acids, which is delivered to the duodenum via the pancreatic duct. </li></ul><ul><li>Neutralizes acid chyme by producing </li></ul><ul><li>NaHCO 3 . </li></ul><ul><li>Secretes enzymes for chemical digestion of all biological molecules. </li></ul>
  29. 29. Small Intestine <ul><li>Up to seven meters in length and 2.5cm in diameter. </li></ul><ul><li>Divided into three sections; the first 30 cm is the duodenum . </li></ul><ul><li>Walls of the small intestine are covered in villi (small finger-like projections), smooth muscle fibers, pits containing intestinal glands secreting enzymes, goblet cells secreting mucus, epithelial cells contain microvilli , and many folds which increase the surface area for chemical digestion and absorption. </li></ul>
  30. 30. Small Intestine
  31. 31. Small Intestine <ul><li>Produces intestinal juice containing H 2 O, mucus, maltase , peptidase and intestinal nuclease . </li></ul><ul><li>Provides optimal pH 8-9 for intestinal nuclease, peptidase and maltase, pancreatic amylase and nuclease, lipase, trypsin. </li></ul><ul><li>Complete digestion of carbs, proteins, nucleic acids, and lipids. </li></ul>
  32. 32. Enzymes at work <ul><ul><ul><ul><ul><li>H 2 O </li></ul></ul></ul></ul></ul><ul><li>starch maltose </li></ul><ul><li>pancreatic amylases </li></ul><ul><li>H 2 O </li></ul><ul><li>maltose glucose </li></ul><ul><li>maltase </li></ul><ul><li> </li></ul><ul><li>H 2 O </li></ul><ul><li>proteins peptides </li></ul><ul><li> trypsin </li></ul>
  33. 33. More enzymes <ul><li>H2O </li></ul><ul><li>peptides amino acids </li></ul><ul><li>peptidase </li></ul><ul><li>H2O </li></ul><ul><li>nucleic acids nucleotides </li></ul><ul><li>pancreatic & intestinal nucleases </li></ul><ul><li>H2O </li></ul><ul><li>lipid droplets glycerol & </li></ul><ul><li>lipase fatty acids </li></ul>
  34. 34. Small Intestine Cont. <ul><li>Absorption of all nutrients/monomers into the villi. </li></ul><ul><li>Receives acid chyme from stomach, secretions from the gall bladder, and pancreas. </li></ul><ul><li>Undigested material is transported to the large intestine by peristalsis . </li></ul><ul><li>Long length allows time for enzymatic reactions to occur and increases absorptive area for monomers/nutrients. </li></ul><ul><li>Increased surface area of intestinal cells by microvilli further increases absorption of monomers/nutrients. </li></ul>
  35. 35. Appendix <ul><li>Worm-like projection arising from the junction of the small and large intestine. </li></ul><ul><li>Vestigial (underdeveloped) organ with no known functions in humans, however, it may have a role in the lymphatic system. </li></ul>
  36. 36. Large Intestine (colon) <ul><li>Up to 1.5 meters long and 7.5 centimeters wide. </li></ul><ul><li>Contains a series of pouches that have a puckered appearance and also contains smooth muscle fibers for peristalsis . </li></ul><ul><li>Houses anaerobic bacteria called E. coli , which synthesizes vitamins B , and K, growth factors, amino acids, and further breaks down undigested materials by fermentation. </li></ul>
  37. 37. Large Intestine
  38. 38. Large Intestine (colon) <ul><li>Absorption of H 2 O from feces and salts, e.g. high [solute] of the feces will cause watery feces/diarrhea (recall B10, hypertonic). </li></ul><ul><li>Secretes mucus for lubrication. </li></ul>
  39. 39. Rectum <ul><li>Last 20 cm of large intestine (colon), </li></ul><ul><li>controlled by a sphincter muscle. </li></ul><ul><li>Compacts/stores feces and opens into anus. </li></ul>
  40. 40. Anus <ul><li>Opening of rectum, surrounded by sphincter muscles. </li></ul><ul><li>Controls opening of rectum. </li></ul><ul><li>Elimination of feces (defecation) by relaxing sphincter muscles. </li></ul>
  41. 41. Swallowing and Peristalsis <ul><li>Swallowing is a reflex action (automatic ) triggered when the bolus is pushed upwards by the tongue against the soft palate and back towards the pharynx . </li></ul><ul><li>The larynx elevates, bends the epiglottis , which covers the glottis in the trachea, to prevent food from entering the lungs. </li></ul>
  42. 42. Peristalsis <ul><li>Peristalsis is the alternating contracting and relaxing of smooth muscles . It occurs in the esophagus moving the bolus to the stomach and provides movement of chyme in the small intestine and undigested material in the large intestine . </li></ul>
  43. 43. Pancreas and Insulin <ul><li>An accessory organ of digestion (exocrine gland), which produces pancreatic juice (H2O, NaHCO 3 , pancreatic amylase, lipase, trypsin, and pancreatic nuclease) and empties into the duodenum via pancreatic duct. </li></ul>
  44. 44. Insulin <ul><li>Also produces a hormone called insulin (from the islets of Langerhans) (endocrine gland) which is secreted into the bloodstream and has the following effects when the concentration of glucose in the blood/blood glucose is high : </li></ul><ul><li>i) Stimulates cells permeability to C 6 H 12 O 6 ; </li></ul><ul><li>stimulates liver, fat, and muscle cells to metabolize C 6 H 12 O 6 . </li></ul><ul><li>ii) Stimulates liver and muscle cells to store excess C 6 H 12 O 6 as glycogen . </li></ul><ul><li>iii) Promotes the buildup of fats and proteins, </li></ul><ul><li>and inhibits their use as an energy source. </li></ul>
  45. 45. Six Major Functions of the Liver <ul><li>Digestive System </li></ul><ul><li>Produces bile (which is stored in the gall bladder) to emulsify lipids. </li></ul><ul><li>Stores excess glucose as glycogen to maintain glucose levels. </li></ul><ul><li>Circulatory System </li></ul><ul><li>Produces blood proteins/plasma proteins from the amino acids (e.g. albumin, gamma-globulin, fibrinogen). </li></ul><ul><li>Detoxifies blood by removing alcohol, drugs, and other poisonous materials. </li></ul><ul><li>Converts Hb from worn out RBCs for the production of bile. </li></ul>
  46. 46. Functions of Liver (5 and 6) <ul><li>Excretory System </li></ul><ul><li>Produces urea from the breakdown of amino acids and excretes it as a N-waste. </li></ul><ul><li>Metabolizes ammonia (N-waste) to urea and excretes it in the urine. </li></ul>
  47. 47. C2 – Enzymes and Digestive Reactions They Promote <ul><li>Introduction </li></ul><ul><li>Enzymes are hydrolytic , that is, adding H 2 O breaks bonds. </li></ul><ul><li>1.) Carbohydrates </li></ul><ul><li>(a) Salivary amylase , produced in the salivary glands; optimal pH 7 . </li></ul><ul><li>(b) Pancreatic amylase , produced in the pancreas; optimal pH 8-9 . </li></ul><ul><li>(c) Maltase , produced in the small intestine (intestinal glands); optimal pH 8-9 . </li></ul>
  48. 48. Enzymes cont. <ul><li>2.) Proteins </li></ul><ul><li>(a) Pepsin , produced in the stomach (gastric glands); optimal pH 2-3 . </li></ul><ul><li>(b) Trypsin , produced in the pancreas; optimal pH 8-9 . </li></ul><ul><li>(c) Peptidase , produced in the small intestine (intestinal glands); optimal pH 8-9 . </li></ul><ul><li>NOTE : pepsin, inactive pepsinogen and trypsin are examples of enzymes called proteases . </li></ul>
  49. 49. Enzymes cont. <ul><li>3.) Lipids </li></ul><ul><li>Lipase , produced in the pancreas; optimal pH 8-9 . </li></ul><ul><li>4.) Nucleic acids/nucleotides </li></ul><ul><li>(a) Pancreatic nuclease , produced in the pancreas; optimal pH 8-9 . </li></ul><ul><li>(b) Intestinal nuclease , produced in the small intestine (intestinal glands); optimal pH 8-9 . </li></ul>
  50. 50. C2 – Components of Digestive Secretions <ul><li>NOTE: * = Enzyme. </li></ul><ul><li>Saliva </li></ul><ul><li>Produced by cells of three pairs of salivary glands located in the head, secreted into ducts which then enters the mouth. </li></ul><ul><li>Composed of: </li></ul><ul><ul><li>H2O </li></ul></ul><ul><ul><li>Mucus </li></ul></ul><ul><ul><li>Buffers </li></ul></ul><ul><ul><li>Salivary amylase* </li></ul></ul>
  51. 51. Gastric Juice <ul><li>Produced by gastric glands and mucus cells in the stomach. </li></ul><ul><li>Composed of: </li></ul><ul><ul><li>H 2 O </li></ul></ul><ul><ul><li>Mucus </li></ul></ul><ul><ul><li>HCl </li></ul></ul><ul><ul><li>Pepsin* </li></ul></ul>
  52. 52. Pancreatic Juice <ul><li>Produced by cells of the pancreas, travels to the pancreatic duct and then to the duodenum. </li></ul><ul><li>Composed of: </li></ul><ul><ul><li>H 2 O </li></ul></ul><ul><ul><li>NaHCO 3 </li></ul></ul><ul><ul><li>Pancreatic amylase* </li></ul></ul><ul><ul><li>Lipase* </li></ul></ul><ul><ul><li>Trypsin* </li></ul></ul><ul><ul><li>Pancreatic nuclease* </li></ul></ul>
  53. 53. Intestinal Juice <ul><li>Produced by intestinal glands and mucus cells in the small intestine. </li></ul><ul><li>Composed of: </li></ul><ul><ul><li>H 2 O </li></ul></ul><ul><ul><li>Mucus </li></ul></ul><ul><ul><li>Peptidase* </li></ul></ul><ul><ul><li>Maltase* </li></ul></ul><ul><ul><li>Intestinal nuclease* </li></ul></ul>
  54. 54. Summary of Enzymes and Chemicals/Molecules <ul><li>1.) Salivary amylase (mouth); breaks down starch + H 2 O  maltose. </li></ul><ul><li>2.) Pancreatic amylase (pancreas to the duodenum); breaks down starch + H 2 O  maltose. </li></ul><ul><li>3.) Maltas e (small intestine); breaks down maltose + H 2 O  glucose. </li></ul>Carbohydrates
  55. 55. Proteins <ul><li>1.) Pepsin (stomach); breaks down proteins + H 2 O  peptides. </li></ul><ul><li>2.) Trypsin (pancreas to the duodenum); breaks down protein + H 2 O  peptides. </li></ul><ul><li>3.) Peptidase (small intestine); breaks down peptides + H 2 O  amino acids. </li></ul>
  56. 56. Nucleic Acids <ul><li>1.) Pancreatic nuclease (pancreas); breaks down nucleic acids + H 2 O  nucleotides. </li></ul><ul><li>2.) Intestinal nuclease (small intestine); breaks down nucleic acids + H 2 O  nucleotides. </li></ul>
  57. 57. Lipids <ul><li>1.) Lipase (pancreas to the duodenum); breaks down lipid droplets + H 2 O  glycerol + fatty acids. </li></ul>
  58. 58. Bile <ul><li>(Produced in the liver, stored in the gall bladder, empties into the duodenum via ducts.) </li></ul><ul><li>NOT an enzyme; (a complex fluid containing H 2 O, electrolytes, bile acids, cholesterol, phospholipids and bilirubin.) </li></ul><ul><li>Emulsifies fats ( physical breakdown ) into fat/lipid droplets, which increases the surface area for chemical digestion by lipase. </li></ul>
  59. 59. NaHCO 3 ( Sodium Bicarbonate) <ul><li>Produced in the pancreas, empties into duodenum via ducts. </li></ul><ul><li>Neutralizes acid chyme from the stomach. </li></ul>
  60. 60. HCl (Hydrochloric Acid) <ul><li>Produced in the stomach. </li></ul><ul><li>Converts pepsinogen (inactive) to pepsin (active). </li></ul><ul><li>Kills bacteria and micro-organisms. </li></ul>
  61. 61. H 2 O (water….in case you forgot) <ul><li>Acts as a solvent. </li></ul><ul><li>Hydrolyzes enzymes. </li></ul><ul><li>Lubricates (aids in movement). </li></ul>
  62. 62. Mucus <ul><li>Produced in goblets cells of the stomach and cells of small and large intestine. </li></ul><ul><li>Lubricates the digestive tract. </li></ul><ul><li>Protection from acid chyme in stomach and small and large intestine. </li></ul>
  63. 63. Cross-section of a Villus: (See following diagram) <ul><li>Villus: </li></ul><ul><li>‘ Finger-like’ projections found on the inner wall of the small intestine and extend into the intestinal lumen. </li></ul><ul><li>Villi (plural) increase the surface area for enzymatic reactions and absorption of monomers/nutrients in the small intestine. </li></ul>
  64. 65. <ul><li>NOTE: The following are examples of how structures of the small intestine are related to its function. </li></ul><ul><li>The numerous villi increase the surface area for absorption of all nutrients. </li></ul><ul><li>The inside of each villus contains a capillary bed to absorb nutrients. </li></ul><ul><li>The inside of each villus contains a lacteal to absorb glycerol and fatty acids. </li></ul>
  65. 66. More examples <ul><li>The small intestine also contains microvilli (“brush border”). They are located on epithelial cells . This also increases the surface area for absorption of monomers/nutrients. </li></ul><ul><li>Epithelial cells are thin, moist and warm which speeds up diffusion/absorption. </li></ul><ul><li>Numerous mitochondria in epithelial cells provide ATP for active transport of nutrients. </li></ul>
  66. 67. And more…. <ul><li>The walls of the small intestine contain smooth muscle cells that provide movement of chyme throughout the entire length. </li></ul><ul><li>This movement is known as peristalsis . Peristalsis also increases the surface area of the food. </li></ul><ul><li>The walls of the small intestine contain goblet cells that produce mucus , which aids in lubrication and movement. </li></ul>
  67. 68. A few more examples <ul><li>The walls of the small intestine also contain many folds , which increase the surfaces area for absorption of monomers/nutrients. </li></ul><ul><li>The length of the small intestine increases the surface are for absorption and chemical digestion of food. </li></ul>
  68. 69. <ul><li>Much of absorption includes active transport , but passive transport also occurs. </li></ul><ul><li>Each villus (and therefore microvillus) contains: </li></ul><ul><ul><li>Epithelial cell s . </li></ul></ul><ul><ul><li>Mucus (goblet cells). </li></ul></ul><ul><ul><li>Lacteal (lymphatic vessel). </li></ul></ul><ul><ul><li>Capillary bed/network. </li></ul></ul><ul><li>They allow for absorption of H 2 O, ions, minerals, and monomers . </li></ul>
  69. 70. Processes of monomers and water entering intestinal epithelial cells <ul><li>Lipids : </li></ul><ul><li>Glycerol and fatty acid monomers diffuse across the epithelial cells and then diffuse into the lacteal vessel . </li></ul><ul><li>These monomers will form triglycerides as they enter the lymphatic system  enters heart and general circulation. </li></ul>
  70. 71. Carbs and Proteins <ul><li>Glucose and amino acid monomers move by active transport into epithelial cells , and then diffuse into capillary bed / network . </li></ul><ul><li>Glucose and amino acid monomers then enter the bloodstream to the liver via hepatic portal vein , exits liver via hepatic vein to the heart, which then pumps C 6 H 12 O 6 and amino acids throughout the body. </li></ul><ul><li>Now the liver can store excess C 6 H 12 O 6 as glycogen and use the amino acids to make proteins. </li></ul>
  71. 72. Nucleic Acids: <ul><li>Nucleotides diffuse into epithelial cells , and then diffuse into capillary bed/network  enter the bloodstream  liver via hepatic portal vein  hepatic vein  heart  body cells. </li></ul>
  72. 73. H 2 O: <ul><li>Enters epithelial cells by osmosis and into the capillary bed/network  enters bloodstream. </li></ul>