1. THE DIGESTIVE SYSTEM

2. PLO’s
C1 - analyze the functional interrelationships of the structures of the digestive system

4. Food – What’s in it for you?

6. Fig. 12.1

7. Digestion
Digestion is the process of breaking down large molecules of food into a form that can be absorbed and utilized by cells of the body
Consists of both physical and chemical processes (What’s the difference?)

10. Mouth Food is broken down physically by chewing
Tongue tastes food and aids in swallowing

11. Salivary glands produce salivary amylase (digests starch)

13. Pharynx Passage for food and air Separates into two separate passages
Swallowing occurs by reflex action
Epiglottis prevents food from entering the trachea

14. Fig. 12.3

15. Esophagus
Food is pushed along by muscular contractions called peristalsis
Cardiac (esophogeal) sphincter is a muscular ring located between stomach and esophagus

17. Stomach Stores food Muscular action mixes food with gastric juice
Gastric glands produce mucus, pepsin, and HCl (pH 2)
Begins digestion of proteins

18. Chemical digestion of protein begins

19. Fig. 12.5

20. Chyme (partly digested food + gastric juice) leaves the stomach through the pyloric sphincter

21. Duodenum
First part of the small intestine, where food enters after it leaves the stomach

22. Sodium bicarbonate neutralizes the pH
Bile enters from the gall bladder (emulsifies fats)
Pancreatic enzymes digest starch, protein and fats

23. Small Intestine Most digestion and absorption occur here
Length and large surface area allow for maximum absorption of food
Material is moved along by peristalsis

24. Blood vessels surround the small intestine
Cells in intestinal wall produces more digestive enzymes

25. Intestinal Villi
Walls contain villi and microvilli to increase surface area for absorption (these contain blood and lymph vessels)

26. Sugars and amino acids enter the blood via capillaries leading to the hepatic portal vein
Fatty acids and glycerol enter lacteals (lymph vessels)

27. Large Intestine (Colon)
No digestion occurs here
Consists of the ascending, transverse, descending and sigmoid colon
Absorption of water, salts and some nutrients

28. Anaerobic bacteria break down indigestible materials and produce some vitamins (vitamin K and B)

29. Feces moves along by peristalsis, is stored in the rectum and exits via anal sphincter

30. REVIEW Animation and quiz
List the structures that food passes through in your body, from beginning to end.
What happens at each location?

31. Accessory Organs
Several organs and glands contribute to the digestive process even though food does not pass through them

32. Pancreas
Cells in the pancreas produce pancreatic juice, which contains sodium bicarbonate and several enzymes to digest carbohydrates, proteins and fats
Pancreatic juice is secreted into the duodenum via the pancreatic duct

33. The pancreas also has an endocrine function (hormone secreting)
insulin is produced in the pancreas and secreted into the blood when blood glucose is high (after eating)
stimulates body cells to take up glucose (lowers and regulates blood sugar levels)
Another hormone, glucagon, is secreted to increase blood sugar levels

35. Liver
Is considered the “gatekeeper” to the blood as it regulates blood composition in several ways

36. Blood leaving the digestive tract first goes to the liver via the hepatic portal vein
Blood leaves the liver via the hepatic vein

37. Liver functions:
Contributes to digestion by producing bile (helps break down fats)
Stores excess glucose as glycogen
Converts glycogen to glucose when needed
Stores iron and some vitamins
Removes and breaks down toxins from the blood
Regulates blood cholesterol levels

38. Synthesizes blood proteins
Produces urea from amino acid breakdown (which is later excreted by the kidneys)
Breaks down hemoglobin from old red blood cells; components of hemoglobin breakdown are excreted in bile, giving it its green colour

39. Gall Bladder Attached to the liver
Stores bile and secretes it into the duodenum via the common bile duct when fats are present

40. Appendix
Not really an accessory organ since it has no apparent digestive function
Found at the end of the cecum (where the small and large intestine join)
Thought to have functions associated with the immune system