Digestive system

1. Digestive system What is the purpose of digestion? • Digestion helps break down food into tiny particles that can be absorbed by our bodies. • Digestion helps us obtain energy and nutrients.

2. Where is your food going when you are eating? What organs will be involved? Digestive System https://www.youtube.com/watch?v=_QYwscALNng

3. Label the organs • Go to echalk, search ‘digestive system’ • Click the first resource • Label the organs in the body (do label the colon, appendix and anus!)

4. Modelling digestion • Aim: We aim to simulate the process of digestion from the mouth to the small and large intestines, and to describe the major functions and purpose of each step. • Materials

5. Methods • Cut up food in to small pieces.  (Simulate the action of your mouth.) • Pour in a small amount of water. • Add a little milk. • Use a mortar and a pestle to mash the food and drink. • Once you have mashed the food in to a liquidy slop then pour it in to a bag to simulate the stomach. • Add a little coke. (This simulates the stomach acid to help break down food) • Use your hands to squeeze the bag in order to mix the food and coke. • Transfer the slurry to the nylon tube and squeeze. (small intestine) • To simulate the large intestine, lay the nylon on multiple paper towels and roll it up tightly. Squeeze and pat it as you can.

6. Questions (explanation of the model) • Explain how step 1 to 4 are similar to what happens in your mouth? • What happens in the stomach to break down the food further? Step 5 to 7. • What does step 8 simulate? What happens at this stage of digestion? • The large intestine is where faeces are forming. What does the body remove from the material at this stage? • What is the material that is left at the end of digestion?

7. Mouth Oesophagus Liver Stomach Gallbladder Pancreas Duodenum Transverse colon Descending colon Ascending colon Appendix Jejunum Ileum Rectum Anus

8. Functions of organs

9. Mouth • Teeth can break and grind the food into small pieces (mastication or physical digestion) • Saliva moistens the food – make it easy to pass the oesophagus • Salivary glands contain enzymes (amylase) to break down starch into smaller molecules (chemical digestion)

10. Oesophagus (gullet) • Muscles in its wall push the food along the oesophagus (peristalsis) • Peristalsis is an involuntary and unidirectional prcoess

11. Stomach • The muscle of the stomach contracts and churns up the food with gastric juices, forming chyme. • Protease in gastric juice (very acidic) breaks down proteins into smaller molecules. • The tissue lining of the stomach is coated with mucus, protecting the stomach from being ‘eaten’ by acidic gastric juices. • If the mucus is destroyed by certain bacteria, stomach ulcer can occur.

12. Liver • It produces bile. • Bile passes through the bile duct into small intestine. • Bile helps break down the fat molecules into small droplets, which can be mixed with the watery liquid - emulsification

13. Gallbladder • It stores the bile. Gallstones • Harderned deposits of bile in the gallbladder • Causes of gallstones: too much cholesterol

14. Pancreas • Endocrine system It secretes insulin to control blood glucose level. • Exocrine system It secretes digestive enzymes: protease, lipase, amylase (pancreatic amylase) Insulin diabetes Blood glucose

15. Small intestine • Most digestion and absorption happens in small intestine. • Digestion • Both bile juice and pancreatic juice secrete into the duodenum, helping digest carbohydrates, lipids and proteins. • Small intestine itself also secretes some digestive enzymes.

16. Absorption Features of small intestine that allows maximum absorption: • Length: 4-6 m long • Narrowness: very thin (3-4 cm)–nutrients can easily pass through the intestinal membrane into bloodstream • Surface area: the membrane lining has finger-like projections on it, called villi; Villi themselves are further composed of fingers, called microvilli

17. Large intestine • The major fuction of large interstine is for water absorption. BUT THIS DOES NOT MEAN THAT MOST OF THE WATER IS ABSORBED IN LARGE INTESTINE! In fact most of the water is absorbed by SMALL INTESTINE! • Flora in the large intestine synthesize vitamins and minerals. • The waste product which is faeces will be stored in the rectum before it is excreted by anus. • Appendicitis: When appendix gets infecction or inflammation

18. Monomers of Carbohydrates Glucose • is the building blocks of starch and cellulose. • We can digest starch but not cellulose. Cellulose-rich foods

19. Amylase Amylase • is the enzyme that breaks down big starch molecules into maltose. • The further breakage of maltose into glucose is done by other enzymes secreted by small intestine. • Amylase is commonly secreted by and Amylase ＊Maltase (small intestine) maltose Starch glucose salivary glands (salivary amylase) pancreas (pancreatic amylase).

20. Monomers of proteins Amino acids • are the basic units of proteins.

21. Protease Pepsin trypsin • is secreted in the stomach; is secreted in the pancreas. • Protease breaks down proteins into peptides. protease *peptidase Amino acids protein peptides

22. Composition of a fat molecule • Fat is made up of and three glycerol fatty acids.

23. Lipase Lipase • breaks down fats into glycerol and fatty acids. • Lipase is secreted by pancreas. lipase + Fat glycerol Fatty acids