Digestion IGCSE


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Digestion IGCSE

  1. 1. DIGESTION B M Subramanya Swamy M.Sc. B.Ed. CIE Co ordinator & Examination Officer Kanaan Global School Jakarta Indonesia subramanyaswamy1591978@gmail.com
  3. 3. Digestion Process by which the body breaks down food (carbohydrates, fats and proteins) into simpler substances These substances are absorbed and used by cells in the body
  4. 4. Types of digestion Types of digestion Process Mechanical  Mastication (chewing, mashing and breaking) into smaller particles  In the mouth, teeth cuts and grinds food. Rolling action of tongue and secretion of saliva rolls food into bolus  Bolus is swallowed and transported through pharynx to stomach by waves of rhythmic contraction called peristalsis Chemical  Changing food into smaller particles through action of enzyme  Involves hydrolysis (addition of water) e.g. amylase converts carbohydrates into simple sugars
  7. 7. MOUTH Functions : analysis material before swallowing, mechanical processing by the teeth, tongue and palatal surfaces, lubricating, limited digestion
  8. 8. TEETH Functions :  Grinding action (mastication) breaks down food  Expose large area for enzyme action child adult
  9. 9. TONGUE Functions :  Rolls food into bolus
  10. 10. SALIVARY GLANDS Secretions Saliva contains:  Water Functions Moisten and soften food  As solvent and for hydrolysis  Mucus  Sticks food together to form bolus maltose  Salivary amylase  Starch 
  11. 11. PHARYNX Function : involuntary action pushes bolus into oesophagus Nasal cavity Palate Oral cavity Tongue Mandible Pharynx
  12. 12. OESOPHAGUS Functions : • Walls made up of circular and longitudinal muscles • Peristalsis transports food to the stomach CARDIAC SPHINCTER Function : • Controls entry of food into the stomach
  13. 13. The swallowing process
  14. 14. Peristalsis Characteristic  Automatic Length of alimentary canal made up circular and longitudinal muscle  Alternate contraction and relaxation of muscle  Result Movement of food down the canal
  15. 15. Peristalsis
  16. 16. STOMACH Secretions Functions Gastric juice Muscular walls churn food into chyme Stored food for 2 – 6 hours Absorbs glucose and alcohol Hydrochloric acid Acidic medium (pH 1) for enzyme action Kills bacteria brought in with food Activates enzymes Water As solvent and for hydrolysis Mucus Protects stomach wall from acidic gastric juice Lubricant for movement of food in the stomach Pepsin Protein Rennin Converts protein into insoluble curds (coagulates milk) for hydrolysis of pepsin. polypeptides
  17. 17. PHYLORIC SPHINCTER Function : controls entry of food into duodenum
  18. 18. Stomach Esophagus Pylorus Fundus Body Pyloric Den Duodenum
  19. 19. Anatomy of the stomach
  20. 20. PANCREAS Secretions Functions Pancreatic juice Hydrolysis of food in duodenum Amylase Starch → maltose Trypsin Polypeptides → peptides Lipase Fats → fatty acids and glycerol Water As solvent for hydrolysis Insulin Excess glucose is converted to glycerol in the liver
  21. 21. LIVER Secretions Dark green bile Functions  Provides alkaline pH  Bile is stored in the gall bladder  Emulsifies fats, provides increased surface area for action of lipase  Neutralise acidic chyme
  22. 22. Anatomy of the liver
  23. 23. Anatomy of the liver
  24. 24. SMALL INTESTINE Secretion Function Intestinal juice Final stage of digestion pH 8 (alkaline) DUODENUM Secretions Erepsin Lactase Sucrase Maltase Water Functions Peptides → amino acids Lactose → glucose and galactose Sucrose → glucose and fructose Maltose → sucrose As solvent and for hydrolysis
  25. 25. JEJUNUM Function : absorption of food ILEUM Function : absorption of food
  26. 26. The region of small intestine
  27. 27. The intestinal wall
  28. 28. The intestinal wall
  29. 29. The intestinal wall
  30. 30. LARGE INTESTINE Function : absorption of water from undigested food CAECUM AND APPENDIX Function :  Vestigial organs with no particular function  Forms junction of small and large intestine COLON Secretion Mucus Function  Peristalsis compact undigested food to form faeces  Lubricates faeces and protects wall from digestive juice
  31. 31. Large intestine
  32. 32. RECTUM Function : stored faeces before defaecation ANUS Function : regulate emptying of rectum
  33. 33. What goes in must come out!
  34. 34. Comparison of human and herbivore digestive system Human Herbivore Food Carbohydrates, Mainly plant proteins fats and proteins and cellulose Alimentary canal Stomach Short Simple Long Caecum Very small Large caecum with cellulase to break down cellulose to glucose  Several chambers  Contains bacteria for digestion of cellulose
  35. 35. ABSORPTION OF DIGESTED FOOD  Nutrients from digested food must be moved from intestines to the bloodstream  This process is called absorption  Almost all of the digested food is absorbed in the ileum  The small intestine is about 6 -7 m long  Water soluble end – products of digestion enter the blood system by diffusion  Fatty acids and glycerol are absorbed by the lacteals  Once inside, fatty acids recombine with glycerol to form globules of fat  They are carried by the lymphatic system to the veins
  36. 36. Structure of the Villi in the Small Intestine
  37. 37. Structure of a villus
  38. 38. Adaptation of the ileum to absorb digested food Features Length Adaptation Longest part of the alimentary canal Internal surface area Internal walls are folded to increase surface area for absorption Villi Further increase surface area for absorption Microvilli Villus covered with epithelial cells The plasma membrane of each cell has minute finger – like projections (microvilli) Further increase surface area Movement Villi move back and forth independently Motion faster after meals Absorption rate increases Membrane Absorption across membrane Either by diffusion or active transport capillary network Dense capillary network close to epithelium Carry away absorbed food particles quickly Maintain concentration gradient between ileum and blood capillaries to aid diffusion
  39. 39. ASSIMILATION Assimilation  uptake and use of food within the body Fate of end products of digestion End – product Fate Glucose  Excess is converted to glycogen (insoluble granules) and stored in the liver  Converted back to glucose when body needs energy and blood sugar level is low  Further excess of glucose is stored as fats in the adipose tissue  Used in cellular respiration Fats  Part of it stored as fats in adipose tissue  Used in synthesis of cell membrane  Utilised in respiration when glucose and glycogen is used up  Fats stored under skin and around organs act as energy store and insulation
  40. 40. Fate of end products of digestion End – product Fate Amino acids  Synthesis of proteins, enzymes and hormones  For growth and development  Excess amino acids are not stored in the body  It is broken down and deaminated in the liver to form ammonia and glycogen (glycogen is stored in the liver) Egestion  In the large intestine water and vitamins (synthesised by bacteria) compact undigested food to form faeces  Propelled along colon and rectum
  41. 41. LIVER • Structure  Large, reddish brown organ  Located just beneath the diaphragm and overlaps the stomach  Plays an important role in metabolism, homeostasis and excretion
  42. 42. • Anatomy
  43. 43. • Vessels associated with the liver Vessels Function Hepatic portal vein  Hepatic artery Carries oxygenated blood to liver Hepatic vein Carries blood containing waste products away from liver Blood capillaries of villi join to form the hepatic portal vein  Carries blood containing end products of digestion from ileum to liver
  44. 44. • Function of the liver Function Mode of action Metabolism of glucose  Regulates the blood sugar concentration in the body  Excess sugars stored as glycogen granules  This occurs in the presence of insulin  When plasma sugar levels fall, glucagon converts glycogen to glucose Metabolism of amino acids  Regulates amount of amino acids in the body  Excess amino acids cannot be stored  Converted during deamination into glucose and urea  Excess glucose is stored as glycogen  Urea is excreted
  45. 45. Function Mode of action Production of bile  Produces bile, which is used in digestion Storage of iron  Excretion of the bile pigment  Synthesis of plasma proteins  Storage of vitamins  Stores vitamin A and D Reservoir for blood  Blood spaces and network of blood capillaries hold a large volume of blood Stores iron from breakdown of haemoglobin  Used in the synthesis of new haemoglobin Haemoglobin is broken down into bile pigments biliverdin and bilirubin  Both pigments are excreted into duodenum as bile pigments Synthesises plasma protein (fibrinogen, serum globulin and serum) from amino acids  They are responsible for the clotting of blood
  46. 46. Function Mode of action Source of heat energy  Metabolically active, producing a large amount of heat energy to replace that lost by the body  Heat distributed to all parts of the body Detoxification  Toxins produced bacteria in large intestines are absorbed and converted to harmless substances in the liver  Liver removes about 95% of alcohol from blood  Alcohol oxidised in the liver to energy  May also be converted to fats  The other 5% lost as sweat, urine and during breathing
  47. 47. DENTITION STRUCTURE Mechanical digestion is carried on in the mouth by the action of the teeth and the tongue.
  48. 48. child adult
  49. 49. Vertical section of molar Crown Enamel Dentine Gum Pulp cavity containing nerves and blood vessels Root Jaw bone Cementum
  50. 50. Tooth structure and function Tooth structure Components Function Enamel Non – living layer of hard calcium salts Dentine Softer bone – like layer Acts as a shock absorber Pulp cavity Contains tooth cells, nerves and blood capillaries Tooth Cement Thin layer of bone – like material Covers Root opening Pathway for blood capillaries and nerves For Protects dentine Forms a hard biting surface cells divide to form dentine Supply food and oxygen to cells dentine of root Holds root in socket blood supply, growth and replacement of tooth Nerves carry messages to and from brain
  51. 51. Tooth structure Components Function Jaw bone with socket Bone made of calcium Tooth fits into socket phosphate of jaw bone Incisor Single root Sharp cutting edge Biting of pieces of food Canine Single root Sharp and pointed Tearing, seizing food Premolar and molar Wide and flat surface Has cusps (points) or ridges Crushing and grinding food
  52. 52. Different types of dental formula Omnivore Carnivore Herbivore Dental formula i:2 c:1 pm : 2 m :3 i:3 c :1 pm : 4 m: 2 i:0 c:0 pm: 3 m: 3 2 1 2 3 3 1 4 3 3 1 3 3 Mode of nutrition Plant and animal Animal Plant Incisor Chisel shaped Sharp and pointed  Canine About the same size as incisors Long, pointed, curved  Diastema X X Upper incisor absent  Small lower incisor, bites against upper horny pad Upper canines absent  Lower canines have sharp edges, bites against upper horny pad 
  53. 53. Omnivore Premolar / molar Surface has small cusps Carnassial teeth Carnivore Surface has sharp, pointed edges X Herbivore Surface flattened with small cusps  X Feeding action  Upper and lower  Upper and lower jaw meet jaw move up and  Grind food with down lateral movements  Scissor – like (side to side) of action lower jaw  Tight jaw attachment  Example Adult human Goat Dog Upper and lower jaw meet  Grind food with lateral movements (side to side) of lower jaw  Loose jaw attachment
  54. 54. Tooth Decay  Dental plaque is the result of bacteria acting on food or sugar stuck on teeth  Tartar is the hard deposit on the teeth caused by bacterial plaque, calcium phosphate and calcium carbonate  It leads to gum disease resulting in gum irritation and swollen gum  As the bacteria in plaque grow, it produces acid in the layer of plaque  This acid destroys the enamel and later, the dentine layer of the teeth  When the decay (cavity) spreads to the pulp cavity, the entire tooth is affected  The result is painful and swollen gum
  55. 55. Prevention of gum disease Prevention Action Taking food rich in calcium, phosphorous and vitamin D Form strong teeth Drinking water or using toothpaste with added fluoride Hardens tooth surface Makes them less susceptible to acids Brushing teeth regularly Remove food particles in teeth Flossing teeth Remove food lodged between teeth Reducing sugar in the diet Reduce bacterial affect Regular dental check up Monitor health of teeth