1. 1 The Digestive System

3. 6.1.1 Why digest food? Food consists of: –Carbohydrates –Lipids –Proteins –Nucleic acids –Minerals –Vitamins –Water These are large, insoluble polymer molecules. They must be digested into monomers small enough to pass through the cell membrane of the cells lining the digestive tract so they can be absorbed in to the blood stream Can be absorbed directly (because of small size), so do not need to be “digested”

5. 6.1.2 Enzymes and digestion Digestion involves hydrolysis of food molecules breaking apart molecules by adding water Hydrolysis of lactose (a disaccharide) into glucose and galactose (both monosaccharides) with the addition of water

6. Digestive enzymes catalyze the hydrolysis of insoluble food molecules to soluble end products Increase the rate The enzyme sucrase catalyzes the hydrolysis of sucrose (a disaccharide) into glucose and fructose (both monosaccharides) with the addition of water

7. 7 Digestive Enzymes Break down complex substances into simpler substances that can be absorbed by the body Digestive Enzymes Complex proteins Complex sugars Fat molecules Amino acids Glucose Fatty acids 6.1.2 Enzymes and digestion

8. Macromolecules need to be digested – Carbohydrates: main source of energy (short term) Complex sugars → Simple sugars – Proteins: growth, antibodies, hormones, pumps, enzymes, carriers Polypeptides → Amino acids – Fats: source of energy (long term)/ storage, absorption, help produce hormones, steroids, part of cell membrane Triglyceride → Fatty acids + Glycerol

9. protease amylase nuclease lipase Enzymes:  Speed up reactions by lowering activation energy (chemical reaction requires less energy to occur) lactase

10. Fig. 5.6 How enzymes work The enzyme remains unchanged!

11. Important Digestive Enzymes Salivary Amylase Pepsin Trypsin Dipeptidase Pancreatic Amylase Lipase

12. 12 Parts of the Alimentary Canal The Digestive System Consists of the alimentary canal (the long tube) and several accessory organs. Parts of the Alimentary Canal mouth pharynx esophagus stomach anal canal large intestine small intestine 6.1.4 Digestive System

14. 14 Organs of the Digestive System Parotid salivary gland Pharynx Esophagus Stomach Pancreas Small intestine Rectum Anal canal Large intestine Duodenum Gall bladder Liver Submandibular salivary gland Sublingual salivary gland Tooth Tongue Mouth

15. 15 Tracing Toast mouthpharynx epiglottis esophagus stomach duodenum jejunum ileum cecum ascending colon transverse colon descending colon sigmoid colon rectum anus feces toast Tracing a piece of toast through the alimentary canal

16. Animation of digestive system

17. Types of Digestion: Mechanical: chewing, mashing, cutting, pounding (mouth / stomach) Chemical: enzymes (speed up chemical reactions)

18. The Digestive Tract Parts of the Digestive Tract –M–Mouth –E–Esophagus –S–Stomach –S–Small Intestine –L–Large Intestine –R–Rectum & Anus

19. Accessory Parts Organs that are not in the digestive tract but help in digestion –T–Teeth –T–Tongue –S–Salivary glands –L–Liver –G–Gall bladder –P–Pancreas

20. The Digestive System

22. Mouth Functions: – Food enters the mouth or oral cavity – Tasting – Mechanical breakdown of food – Secretion of saliva (by the salivary glands)

23. Anatomy of the Mouth

24. Mouth Tongue – M– Mixes and rolls food into tiny mashed up bits (Bolus) – Pushes the bolus toward the esophagus when swallowing.

26. Salivary Glands Salivary glands – produce and secrete saliva into the oral cavity. – Parotid (beneath the cheeks) – S– Submaxillary (below the jaw bone) – S– Sublingual (below the tongue)

27. Saliva Saliva moistens the food and contains enzymes that begin digestion of starch into smaller polysaccharides. From wikipedia: –Salivareferred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most animals.

28. Important Digestive Enzymes Salivary Amylase is the 1 st enzyme and begins working on starches to break them down into simpler sugars. They are secreted by the salivary glands and active in the mouth. It’s optimal pH range is about 7.0.

29. Anatomy of the Mouth and Throat

30. Esophagus A straight muscular tube that is about 10 inches (25 cm) long which connects the mouth to the stomach Food takes about 4 to 8 seconds as it passes through to the stomach. Its walls contain smooth muscles that contracts in wavy motion (Peristalsis). Peristalsis propels food and liquid slowly down the esophagus into the stomach. Cardiac Sphincter (ring-like valve) relaxes to allow food into the stomach.

32. Peristalsis in the Esophagus Peristalsis Video

33. Stomach J-shaped muscular sac, where most digestion occurs. Has inner folds (rugae) that increase the surface area of the stomach.

34. Stomach Gastric Juices Food is mixed with gastric juices secreted by the stomach wall Hydrochloric acid (HCl) activates enzymes, breaks down food molecules and kills bacteria Enzymes (proteases) break down proteins Mucus lubricates food and protects the stomach wall from HCl.

35. Stomach Churns and grinds together the bolus into smaller pieces. Converts the bolus into a liquid (chyme) after 4 hrs of mechanical and chemical digestion Chyme passes through the pyloric sphincter into the small intestine.

36. AKA Cardiac Sphincter

37. Movements in Stomach

38. Important Digestive Enzymes Proteases are a group of enzymes that hydrolyze proteins into amino acids (or smaller pieces of proteins). Pepsin Trypsin Dipeptidase

39. Important Digestive Enzymes Pepsin is the major stomach enzyme and begins working on proteins to break them down into smaller polypeptides. It is secreted by the stomach cells and is active in the stomach. It’s optimal pH range is about 2.0.

40. The Stomach

41. Label the Stomach (a) Lumen of the stomach which stores the food from a meal (b) Gastric pits from which mucus, enzymes and acid are secreted (c) Mucus secreting cells. Mucus protects the surface of the stomach from auto-digestion (d) Parietal cells that produce HCL which kills microorganisms that enter the digestive system (food & tracheal mucus). This also converts inactive pepsinogen to active pepsin (e) Chief cells: produces pepsinogen, a protease enzyme

43. Small Intestine Long (20 ft), coiled tube beneath the stomach. This is where digestion is completed and products are absorbed into the bloodstream. Has three parts: Duodenum – upper part; about 10 in; connected to the stomach. Where the digestive juices from the pancreas and the liver combine with chyme. Sodium bicarbonate (pH 9) is secreted to neutralize the acid. Jejunum – about 8 ft; completion of digestion Ileum – about 12 ft; absorption of nutrients

44. Site of greatest amount of digestion and absorption

45. Important Digestive Enzymes Trypsin breaks down polypeptides into smaller peptides. They are secreted by the pancreas and active in the duodenum of the small intestine. It’s optimal pH range is about 8.0.

46. Important Digestive Enzymes Dipeptidase breaks down peptides into amino acids. They are secreted by the small intestinal cells and active in the small intestine. It’s optimal pH range is about 8.0.

47. Important Digestive Enzymes Pancreatic Amylase finishes carbohydrate digestion by breaking down starch into the disaccharide maltose. They are secreted by the pancreas and active in the small intestine. It’s optimal pH range is about 7.0.

48. Important Digestive Enzymes Lipase enzymes work on lipids to break them down into glycerol and fatty acid chains. Pancreatic lipase is secreted by the pancreas. It’s optimal pH is 7.2.

49. Small Intestine Takes about 4 – 8 hrs to complete its journey. Mucosa (inner wall) – secretes several enzymes that acts on the food. Where the pancreatic enzymes are emptied into. Digested nutrients are absorbed through intestinal walls into the blood supply. Peristalsis moves the undigested food along.

50. Has folded inner walls covered with fingerlike projections (villi; sing. – villus) Each villus has tinier projections called microvilli that absorb digested food. Villi and microvilli increase the surface area of the small intestine for greater absorption.

51. The Small Intestine

52. Label the Small Intestine (a) Villus which increases the surface area for absorption of the products of digestion (b) Microvilli border of the epithelial cell increases the surface area for absorption. (c) Lacteals are vessels that transport lipids out of the small intestine into the lymphatic system. (d) In the wall of the small intestine are the blood vessels to transport absorbed products to the general circulation. There are also muscles to maintain peristalsis

53. Absorption vs. Assimilation Soluble products are taken up into the epithelial cells of the small intestine. The products then diffuse into the bloodstream. Soluble products are transported through the blood to body tissues. The cells of these tissues absorb them for their own use or storage.

54. Absorption vs. Assimilation

55. How absorption happens The structure of the villi increases the surface area for the absorption of digested food molecules.

56. (a) folds increase SA:VOL ration by X 3 (b) Villi project into the lumen of the gut increasing the surface area by X 10 (c) Microvilli are outward folds of the plasma membrane increasing the surface area another X10

57. Diagram a villus Using the red textbook (page 860), draw and label a villus from the human small intestine. Include the following labels: villi, microvilli, capillaries, lacteals, epithelial cells, lymph vessel

58. Large Intestine a.k.a. Colon larger diameter, but shorter (5 ft) Water is absorbed from the undigested food making the waste harder until it becomes solid. Waste stays for 10 – 12 hours.

60. Waste is pushed into the expanded portion (rectum) of the large intestine. Solid waste stays in the rectum until it is excreted through the anus as feces. Appendix hangs on the right side of the large intestine.

61. The Large Intestine

62. The “Colon” (a) The lumen of the colon (b) The mucus producing goblet cells (c) Muscular walls to maintain peristalsis

63. Accessory Organs Produce or store enzymes that helps in digestion.

64. Accessory Organs Liver –L–Largest solid organ of the body –I–It weighs 1.6 kg. and is 20 cm. across. –P–Produces bile (watery, greenish substance), which aids in the absorption of fats. –S–Secretes bile to the gall bladder

65. The Liver –Stores vitamins A,D,E,K –Stores sugar and glycogen –Synthesizes proteins –Eliminates biochemical products (RBCs) –Detoxifies drugs, alcohol, and environmental toxins.

66. Accessory Organs Gall bladder – Stores bile in between meals ecretes bile to the duodenum through the bile duct during mealtime. Bile contains bile salts, pigments, cholesterol and phospholipids. Bile is an emulsifier NOT an enzyme. Emulsifier – dissolves fat into the watery contents of the intestine.

67. Gall Bladder

68. Accessory Organs Pancreas – Produces a juice that contains enzymes to break down carbohydrates, fats and protein. – Secretes the juice into the duodenum through the pancreatic duct. –A–Also secretes hormones, like insulin.

69. The Pancreas

71. Path of Digestion Mouth Esophagus Stomach Small Intestine Large Intestine Anus

72. Let’s see what happens!