1. Digestion

2. The process of digestion has 5 functions:
The Digestive System
The process of digestion has 5 functions:
Ingestion: taking food into the body
Digestion: breakdown of insoluble substances into soluble ones
Absorption: uptake of soluble substances into cells
Assimilation: how cells use food
Egestion: removal of undigested waste

3. Digestion
Egestion
faeces
Ingestion
Absorption

4. Food is broken down into smaller pieces by biting, chewing,
churning, bile action.
These pieces are not soluble but have a large surface area for enzymes to work on.

5. Surface area = 24 cm2 Volume = 8 cm3 SA : V ratio = 24:8 = 3:1

6. Enzymes break chemical bonds to make insoluble food particles soluble.
Carbohydrases break down carbohydrates into sugars
Proteases break down proteins into amino acids
Lipases break down fats (lipids) into fatty acids and glycerol

7. model gut experiment
boiling
tube

8. What do you
remember

9. Add gall bladder, bile duct, sphincter Buccal cavity Salivary gland
Oesophagus
Liver
Stomach
Duodenum
Pancreas
Worksheet to go with this
Ileum
Colon
Appendix
Rectum
Anus

11. The ball of food is called a bolus
The Mouth
Mechanical: chewing, biting
Chemical: Saliva from the salivary glands contains the enzyme CARBOHYDRASE.
Starch + carbohydrase  sugar (maltose)
The ball of food is called a bolus

12. NO FOOD IS BROKEN DOWN HERE
The oesophagus
NO FOOD IS BROKEN DOWN HERE
Muscles in the wall of the oesophagus contract, pushing food down to the stomach. This is called PERISTALSIS

13. peristalsis

15. Muscles in wall contract
Oesophagus wall
FOOD
Food moves
forwards
PERISTALSIS

16. The stomach
The strong muscle walls contract to churn and mix food with stomach juices called GASTRIC JUICES.
Cells in the stomach wall produce a protease enzyme that digests proteins, breaking them down into amino acids.

17. The stomach cells also produce hydrochloric acid HCl, which
Lowers the pH for the protease enzyme to work
Kills bacteria
Stops salivary amylase from working
A circular, sphincter muscle at the exit of the stomach opens to allow food into the small intestine.
It controls release of food from the stomach.

18. This is called emulsification.
The liver
Bile, made in the liver and stored in
the gall bladder passes along the
bile duct into the duodenum.
Bile breaks fats into very small
droplets, increasing the surface area
for enzymes to work on.
This is called emulsification.
Bile is alkaline and therefore also neutralises acid from the stomach.

19. passes into the gall bladder
bile made in the liver
passes into the gall bladder
gall bladder
digestive enzymes
produced in pancreas
pancreatic
duct
bile duct
duodenum

20. The duodenum ENZYMES are added to the duodenum from: The pancreas
The wall of the duodenum
Carbohydrases break down starch to sugars
Proteases break down protein to amino acids
Lipase breaks down fat to fatty acids and glycerol

21. Main function is absorption.
The ileum
Main function is absorption.
The walls are adapted for efficient diffusion of the soluble products of digestion.

22. villus muscle layer ridge covered with villi network of blood
capillaries
lacteal
absorbs
fatty acids
villus
muscle
layer
arteriole
venuole

23. A villus ileum wall blood capillaries lacteal sugar amino acids
fatty acids
lacteal
to liver

24. how the ileum is adapted for absorption
Long length (5m), folds and villi increase the surface area for absorption
Villi contain blood vessels to carry away absorbed nutrients
Villi contain lacteals to carry away absorbed fats
The walls are thin, one cell thick, and permeable to form a short diffusion distance

25. The absorbed nutrients, amino acids and sugars are carried in the blood to the liver in the
HEPATIC PORTAL VEIN.

26. NO DIGESTION OCCURS HERE
the colon
NO DIGESTION OCCURS HERE
The colon has a large surface area for the absorption of water
from the fluid we drink, food we eat, mucus and digestive juices.
It also absorbs mineral salts.

27. the rectum & anus
Solid waste made up of undigested food, bacteria and cells from the gut
forms faeces,
which is stored in the rectum before passing out of the body through the anus.

28. transverse
colon
descending
colon
ascending
colon
rectum
appendix
anus

29. Summary bbc learning zone clip 4180

30. dvd

31. Cut & stick activity