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Lesson 2

Lesson 2. How does food move down the oesophagus?. Journey of Food. 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. Oesophagus.

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Lesson 2

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

  2. Journey of Food

  3. 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.

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

  5. Motility in the oesophagus • The canal has layers of muscles in its walls: • Circular muscles • Longitudinalmuscles

  6. 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.

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

  8. Digestion in the stomach

  9. Overview Stomach Role of Digestion Mouth & Oesophagus Large Intestine & Others Gall Bladder &Pancreas Small Intestine

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

  11. How does the giraffe drink?

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

  13. 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.

  14. Recall….

  15. A closer look Ss

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

  17. Overview Stomach Role of Digestion Mouth & Oesophagus Large Intestine & Others Gall Bladder &Pancreas Small Intestine

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

  19. 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.gif

  20. 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.

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

  22. Function of Hydrochloric acid in the stomach 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

  23. 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? Hydrochloric acid Pepsinogen Pepsin Hydrochloric acid Prorennin Rennin

  24. Enzymes (Proteases) in the stomach Soluble milk protein (caseinogen) Rennin Insoluble protein (casein) Polypeptide

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

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

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