Ch 38-2 The Process of Digestion

1. Ch 38-2 The Process of Digestion By the end of this section you should be able to: Identify the organs of the digestive system Describe the function of the digestive system

2. Ch 38-2 The Process of Digestion alimentary canal – one-way tube that passes through the body

3. Ch 38-2 The Process of Digestion digestive system – helps convert foods into simpler molecules that can be absorbed and used by the cells of the body

4. Ch 38-2 The Process of Digestion – includes: mouth pharynx esophagus small intestine  large intestine stomach

5. Ch 38-2 The Process of Digestion accessory structures: add secretions to the digestive system  pancreas liver salivary glands

6. Ch 38-2 The Process of Digestion

7. Ch 38-2 The Mouth mechanical digestion – physical breakdown of large pieces of food into smaller pieces

8. Ch 38-2 The Mouth chemical digestion – breakdown of large food molecules into smaller food molecules with digestive enzymes

9. Ch 38-2 The Mouth mouth– the organ in which digestion begins teeth– tear and crush food into a fine paste until it is ready to be swallowed – anchored to the bones of the jaw; protected by a coating of enamel – do much of the mechanical digestion

10. Ch 38-2 The Mouth saliva – secreted by salivary glands as the teeth cut and grind food – secretion is controlled by the nervous system; can be triggered by scent

11. Ch 38-2 The Mouth three functions: 1) helps to ease the passage of food through the digestive system by moisteningfood 2) contains lysozyme – an enzyme that fights infection by digesting the cell walls of bacteria that enter the mouth 3) contains amylase – begins to break the bonds in starches to produce simpler sugars

12. Ch 38-2 The Esophagus bolus – chewed clump of food that is pushed down the throat by the tongue and throat muscles epiglottis– flap of tissue that covers the trachea when swallowing to prevent food from entering lungs

13. Ch 38-2 The Esophagus esophagus – tube that connects the throat (pharynx) to the stomach – walls are made of ringed muscle that squeeze food through the tube – peristalsis – the rhythmic muscular contractions of the smooth muscle in the digestive system that pushes food along

14. Ch 38-2 The Esophagus cardiac sphincter – also called esophageal sphincter – a thick ring of muscle that closes the esophagus after food has passed into the stomach – prevents the contents of the stomach from moving back into the esophagus

15. Ch 38-2 The Esophagus heartburn – backflow of stomach acid across the cardiacsphincter – can be caused by overeating, overdrinking, or excess caffeine

16. Ch 38-2 The Stomach stomach – large, muscular sac just below the diaphragm in the abdomen – three layers of smooth muscle – churns and mixes the food that is swallowed

17. Ch 38-2 The Stomach chemical digestion – stomach is lined with millions of microscopic gastric glands that release a number of substances into the stomach

18. Ch 38-2 The Stomach gastric secretions include: 1) mucus – lubricates food and protects the stomach lining 2) HCl – hydrochloric acid makes the stomach contents acidicwhich allows pepsin to work

19. Ch 38-2 The Stomach gastric secretions include: 3) pepsin – enzyme that begins the digestion of protein – works best in acidic environments – breaks proteins into smaller polypeptide fragments

20. Ch 38-2 The Stomach the acidic environment denatures (“changes the shape of”) the amylase enzyme, so carbohydrate digestion stops in the stomach (it restarts in the small intestine)

21. Ch 38-2 The Stomach mechanical digestion – muscular walls of the stomach contract to churn and mix stomach fluids and food to produce chyme ▫ chyme – a pasty mixture of food that results after 2 to 3 hours of churningin the stomach

22. Ch 38-2 The Stomach pyloric valve – a ring of muscle between the stomach and small intestine – opens to allow chyme to flow into the small intestine

23. Ch 38-2 The Stomach

24. Ch 38-2 The Small Intestine The Small Intestine three sections: duodenum jejunum 3) ileum

25. Ch 38-2 The Small Intestine duodenum– firstof the three parts of the small intestine – where almost all of the digestiveenzymes enter the intestines – chyme mixes with enzymes and digestive fluids from the pancreas, liver, and the lining of the duodenum

26. Ch 38-2 The Small Intestine intestinal secretions 1) peptidase – breaks down dipeptides into amino acids 2) maltase, sucrase, and lactase – breaks down remaining disaccharideinto monosaccharides

27. Ch 38-2 The Small Intestine accessory structures: pancreas– long glandlocated behind the stomach – gland that serves three functions: 1) produces hormones that regulate blood sugar levels 2) produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids

28. Ch 38-2 The Small Intestine 3) produces sodium bicarbonate to neutralize HCl from stomach acid – because pancreatic enzymes only work in a neutral environment

29. Ch 38-2 The Small Intestine liver – large, brownish organ located just above and to the rightof the stomach – secretes bile – yellow-brown liquid loaded with lipids and salts – acts like a detergent - breaks fat into smaller and smaller droplets which make it possible for enzymes to reach more surface area

30. Ch 38-2 The Small Intestine gallbladder – pouch-like organ behind the liver that stores bile

31. Ch 38-2 The Small Intestine

32. Ch 38-2 Absorption in the Small Intestine jejunum and ileum– last two sections of the small intestine – approximately 6 meters long – at this point chemical digestion is complete

33. Ch 38-2 Absorption in the Small Intestine – nutrient molecules are absorbed from these two sections into the bloodstream – peristalsis move the chyme along the jejunum and ileum

34. Ch 38-2 Absorption in the Small Intestine villi – finger-like projections that increase the surface area of the walls of the small intestine

35. Ch 38-2 Absorption in the Small Intestine microvilli – thousands of even tinier finger-like projections found on the surfaceof the cells of the villi! – inside eachvillus is a network of capillaries and lymph vessels

36. Ch 38-2 Absorption in the Small Intestine absorption – nutrients are absorbed into the cells of the villi lining the small intestine – carbohydrates and proteins are absorbed into capillaries – undigested fat and some fatty acids are absorbed into lymph vessels

37. Ch 38-2 Absorption in the Small Intestine

38. Ch 38-2 Absorption in the Small Intestine when food leaves the small intestine, it is nutrient-free only water, cellulose, and other undigestible substances remain

39. Ch 38-2 Absorption in the Small Intestine appendix – small sac-like organ in small intestine that does little to promote digestion – can be clogged and inflamed - appendicitis

40. Ch 38-2 The Large Intestine large intestine,or colon– removes water from undigested material that is left – bacterial colonies produce compounds like vitamin K concentrated waste material passes through the rectum and is eliminated

41. Ch 38-2 Digestive System Disorders GERD– gastroesophagealreflux disease – chronic heartburn in 25-35% of people – symptoms – heartburn, regurgitation, difficulty swallowing

42. Ch 38-2 Digestive System Disorders causes – defects in esophageal sphincter; – slower than normal emptying of the stomach; – decreased secretion of bicarbonate by the esophagus – treatments – lifestyle changes; medication to control stomach acid; surgery

43. Ch 38-2 Digestive System Disorders peptic ulcer – hole in stomach lining produced by the powerful acidsreleased into the stomach – most are caused by Heliobacter pylori; can be cured with antibiotics

44. Ch 38-2 Digestive System Disorders diarrhea – irritation or infection that interferes with the removal of water from the largeintestines

45. Ch 38-2 Digestive System Disorders constipation – condition resulting from the removal of too much water from the undigested material in the large intestine

46. Ch 38-2 The Process of Digestion By the end of this section you should be able to: Identify the organs of the digestive system Describe the function of the digestive system

47. Ch 38-2 The Process of Digestion Identify the organs of the digestive system Mouth, pharynx, esophagus, stomach, small intestine, and large intestine Describe the function of the digestive system

48. Ch 38-2 The Process of Digestion Describe the function of the digestive system To convert food into simple molecules that can be absorbed and used by the cells of the body

49. Ch 38-3 The Excretory System By the end of this section you should be able to: Describe the functions of the kidneys Explain how blood is filtered

50. Ch 38-3 Functions of the Excretory System excretion – process by which metabolic wastes are eliminated – maintains homeostasis in the internal cellular environment – rids the body of excess salt, CO2 and urea – urea – toxic compound that is produced when amino acids are used for energy