Which enzyme does saliva contain? Which enzyme works best in acidic condition? What is digestion?

1. Which enzyme does saliva contain? Which enzyme works best in acidic condition? What is digestion? Where does digestion begin? Where does digestion end? The small intestine is divided into two parts. They are called _____ and ______.

2. Digestive System Teeth Tongue Salivary Glands Oesophagus Liver Gall Bladder Stomach Pancreas Small Intestine Large Intestine Rectum Anus

3. The beginning – in the Mouth • Digestion begins in the mouth where food is broken down by the teeth. This is an example of physical breakdown. The small parts of food are mixed with saliva and swallowed.

4. Saliva contains enzymes that start to chemically breakdown some of the carbohydrates (starch) in the food. • The enzymes in the saliva are called amylase.

5. Enzymes in Action

6. Enzymes Enzymes are catalysts that speed up chemical reactions in living organisms. Enzymes are specific (e.g. protease can only break down proteins) Enzymes are affected by pH (e.g. protease works much faster in an acidic condition) Enzymes are affected by temperature (body temperature of 37oC is optimal)

8. Through the Oesophagus! • After being chewed and mixed with saliva, the food then passes the epiglottis, a flap of skin and cartilage that prevents food from entering the trachea (air tube).

10. Peristalsis • The food is then moved down the oesophagus with the help of wave like contractions, a process called peristalsis.

12. What happens next?

13. In the Stomach The stomach stores and physically break down food by churning. The stomach also produces hydrochloric acid (pH 2) and protease enzyme for chemical breakdown of proteins. The walls of stomach is unaffected by the acid because they are protected by the mucus produced by the stomach wall cells.

14. Stomach Acid (HCl Acid) = pH 2

17. BacTerial War

18. Write the answers on your book Describe two things happening to the food in the stomach Give the name of the enzyme present in the stomach Describe why stomach acid is needed Describe why stomach acid normally does not affect the stomach walls.

19. Next stop - Duodenum • The contents of the stomach are then moved to the first part of small intestine – Duodenum. • Here, the chyme is mixed with bile and pancreatic juice.

20. duodenum (first part of small intestine) ileum (second part of small intestine)

21. Liver Pancreas Duodenum

22. Mmmmmm… Bile! • Bile is a greeny-yellow substance made by the liver but stored the gall bladder which emulsifiesfats to allow absorption . • It also neutralizes the chyme before entering the duodenum

23. Mmmmmm… Pancreatic Juice!! The pancreas produces the pancreatic juice which contains: • Pancreatic amylase • Pancreatic protease • Pancreatic lipase The juice completes all the chemical break down of food particles.

24. Lipase ♥ Bile (page 32) Bile breaks up large fat globules into many tiny droplets. This greatly increases the surface area of the fat, enabling the lipases included in the pancreatic juice to digest the fat much faster. Bile also neutralises the acidity of the ‘chyme’ from the stomach.

25. Write the answers on your book Bile is produced in ______ and stored in ___________. Describe the two functions of bile. What are the contents of pancreatic juice? Fully describe what happens to the food in the duodenum

26. Absorption in ileum – Dialysis Tubing Experiment Aim:to investigate how nutrients are absorbed into the blood Method: Tie one end of the dialysis bag tightly with string Fill the “sausage” with the solution of glucose and starch Tie the other end of the dialysis bag tightly with string Place in a beaker of water Add a few drops of iodine until the beaker goes a light orange colour water glucose + very thin dialysis bag starch

27. Sausage Questions What happened to the sausage and water? What do you think happened to the starch molecules inside the sausage? What do you think happened to the glucose molecules inside the sausage?

28. duodenum (first part of small intestine) ileum (second part of small intestine)

29. Here is a question to think about… Why do we have to “digest” food that we eat?

30. Here is another question to think about… What happens to the food after being digested?

34. duodenum (first part of small intestine) ileum (second part of small intestine)

35. Malnutrition

36. So what happens to the food after being digested? We must digest (break down) food into very tiny particles, so they can be absorbed into the blood stream. The blood then carries the nutrients everywhere so they can be used by the cells of the body! (energy, growth and repair)

37. Absorption!!! Most of the nutrients are absorbed in the ileum (the second part of the small intestine) Then water is absorbed in the large intestine.

38. Digestive System Teeth Tongue Salivary Glands Oesophagus Liver Gall Bladder Stomach Pancreas Small Intestine Large Intestine Rectum Anus

39. Digestion is now over… what now? - ileum • After digestion is completed, the broken down nutrients are absorbed into the blood stream • The absorption first takes place in the second part of the small intestine – ileum.

40. Villi The walls of the small intestine are not smooth. They are covered in villi

44. You must be able to describe how villi in the small intestine are adapted for maximum absorption of nutrients!!!

45. How it is maximised…. • Large surface area • Large blood supply • Thin surface to move across • Blood has low concentration of nutrient which increases the rate of diffusion

46. Q: Discuss the importance of the villi and how the structure of the villus aids the absorption of food in the ileum How to answer: Define terms (e.g. ileum, villi) Describe the structural features of villi (e.g. very think skin) Describe how each feature aids the absorption of food (e.g. micro villi = increase in surface area = greater absorption)

47. Absorption in the ileum(page 35) Ileum is the second part of small intestine where absorption of nutrients from digested food occurs. The finger-like projections called villi maximise the absorption process by increasing the surface area where nutrients can enter the blood stream. Villi have very thin surface so nutrients can easily be absorbed and they are well supplied with blood to allow many nutrients to be absorbed into the blood stream.

48. Finally - Large Intestine • After the long trip through the small intestine, the remains enter the large intestine. • Here remains are fermented by the action of gut bacteria, excess water is absorbed and faeces is stored until released.

49. Digestion Quiz – Ready?