2. Lesson 2 How does food move down the oesophagus?

3. Journey of Food

4. Peristalsis The muscles in the wall of the canal cause rhythmic, wave-like contractions called Peristalsis. This process can be visualized as a squeezing action, forcing the food along.

5. Oesophagus Food moves on to the stomach by peristalsis. Any Digestion? No digestion

6. Motility in the oesophagus The canal has layers of muscles in its walls: Circular muscles Longitudinal muscles

7. Peristalsis When the circular muscle contracts, the longitudinal muscle relaxes causing the gut wall to constrict thus squeezing and pushing the food forward. When the longitudinal muscle contracts, the circular muscle relaxes and the gut dilates becoming wider for food to enter.

9. Circular muscles above the bolus contracts Circular muscles below the bolus relaxes http://www.westga.edu/~lkral/peristalsis/index.html

10. Digestion in the stomach

11. Overview Role of DigestionMouth & Oesophagus Gall Bladder &Pancreas Stomach Large Intestine & Others Small Intestine

12. The last lesson The physical and chemical digestion in the mouth The structure of oesphagus and stomach The process of peristalsis

13. How does the giraffe drink?

14. Giraffe Tallest animals in the world Range from 3m -5m tall Drinking – Going against gravity? Your ideas?

15. Eat and drink in space? No gravity Eating and drinking – possible in the absence of gravity? If yes, Why? If no, Why? An astronaut eating a piece of Cornflake in space.

16. Recall….

18. A closer look Ss

19. Today’s lesson The chemical digestive process in the stomach

20. Overview Role of DigestionMouth & Oesophagus Gall Bladder &Pancreas Stomach Large Intestine & Others Small Intestine

21. Digestion in the stomach The stomach is a muscular bag which contracts and relaxes to mix the food. In here: Digestion Of only PROTEINS

22. Peristalsis revisited How does peristalsis play a role in the stomach? Continual contractions & relaxations of stomach wall muscles result in a churning action Physical digestion Breaks up food particles  ↑ SA / V of ingested food Mixes food well with gastric juice for efficient enzymatic action Picture from: http://wwwartsci.clarion.edu/biology/bbarnes/digestivesystem/stomach/stomach_peristalsis.gifhttp://wwwartsci.clarion.edu/biology/bbarnes/digestivesystem/stomach/stomach_peristalsis.gif

23. Stomach Main function: store food  turn it into liquid ( chyme )  release it in small quantities at a time to the rest of the gut Stores food temporarily for 3 to 4 hours.

24. Contains gastric glands : secrete gastric juice that mixes with food to form chyme Gastric juice: water + enzymes + hydrochloric acid  pH around 2.0

25. Function of Hydrochloric acid in the stomach FunctionsActions Digestion Anti-bacterial Neutralisation Optimal pH Activates the enzymes pepsin Kills harmful bacteria ingested with food Neutralizes the alkaline saliva from the mouth (i.e. stops the action of salivary amylase) Lowers pH to pH 2 at which the gastric enzymes work best

26. Conversion of inactive form of enzymes to active form Both enzymes are secreted are produced as inactive form – pepsinogen & prorennin Why must both enzymes be secreted in the inactive form? Pepsinogen Hydrochloric acid ProrenninRennin Pepsin Hydrochloric acid

27. Enzymes (Proteases) in the stomach EnzymesEnzymatic actions Substrate Product Pepsin (Active)Protein Polypeptide Rennin Soluble milk protein (caseinogen) Insoluble protein (casein)

28. What we have learnt Oesophagus Narrow, muscular tube 2 layers of muscles LongitudinalCircular is a with outerinner Rhythmic, wave-like contractions Antagonistic which are producing Peristalsis Downward movement of food Stomach known as responsible for into

29. What we have learnt Stomach Distensible, muscular bag Gastric glands Gastric juice HClEnzymes Churning action Physical digestion Amylase action Acidic medium Bacteria PepsinRennin Proteins Polypeptides Caseinogen Casein Chemical digestion Chyme Pyloric sphincter Small intestines Smaller pieces is a withwhich produces which secrete containing resulting in breaking food into for effective action by stops creates kills responsible for such as digests into activates converts into making up part of which passes through into