the liver plays a key role in digestion and metabolism.

1. HUMAN NUTRITION
DIGESTIVE SYSTEM

2. THE ALIMENTARY CANAL
• INGESTION: taking substances (e.g. food, drink) into the body
through the mouth.
• DIGESTION: the break-down of large, insoluble food
molecules into small, water-soluble molecules using
mechanical and chemical processes.
• ABSORPTION: the movement of digestive food
moleculesthrough the wall of the intestine into the blood or
lymph.
• ASSIMILATION: the movement of digestive food molecules
into the cells of the body where they are used, becoming part
of the cells.
• EGESTION: the passing out of food that has not been
digested, as faeces, through the anus.

4. Name the layers of tissue that make
up the alimentary canal, starting
from the inside

5. PERISTALSIS
A contraction in one region of the alimentary canal is followed by another contraction
just below it so that a wave of contraction passes along the canal pushing food in front
of it.

6. DIGESTION:
-Physical: teeth and churning
movements of the alimentary canal
-Chemical: enzymes

8. Chemical digestion
FOOD ENZYMES FINAL PRODUCTS
Starch amylase glucose
Proteins protease Amino acids
Fats lipase Fatty acids +
glycerol

9. MOUTH
-Ingestion
-Digestion
Food is chewed and mixed with
saliva.

13. How to reduce the risk of tooth
decay
-Eating food with a low sugar content.
- Regular and effective brushing of teeth at
least twice a day to prevent the build up of
plaque.
- Use a fluoride toothpaste regularly. It
makes your teeth more resistant to decay

14. Chemical digestion (mouth)
• Saliva: contains salivary amylase
starch → maltose

15. SWALLOWING
• Ensures that food does not enter the windpipe
(trachea) and cause choking.
• Beginning: voluntary
• Then: involuntary

17. STOMACH

18. STOMACH
• Functions:
- stores food from a meal.
- turns food into a liquid (peristaltic
movements)
- releases food in small quantities at a time to
the rest of the alimentary canal (pyloric
sphincter)

19. Chemical digestion:
• Production of gastric juice (glands in the
lining)
- Enzyme: pepsin (protease)
Proteins → peptides
- Hydrochloric acid: provides the best degree of
acidity for pepsin to work in and kills many bacteria
of food.

20. THE SMALL INTESTINE
Duodenum Ileum
• Chemical digestion
Enzymes from:
1. Pancreatic juices
2. Bile
3. Intestinal juices

21. Liver, gall bladder, duodenum and
pancreas

22. PANCREAS
• Secretion of pancreatic juice:delivered to the
duodenum by the pancreatic duct.
i) Enzymes:
-Proteases:
Proteins → peptides → aa
- Pancreatic amylase:
Starch → maltose
- Lipase:
Fats → fatty acids + glycerol
ii) Sodium hydrogencarbonate: neutralizes the acid liquid from
the stomach so that pancreatic enzymes work correctly. (alkaline conditions)

23. BILE
• Produced by the liver.
• Stored in the gall bladder.
• Delivered to the duodenum by the bile duct.
• No enzymes
• Bile pigment:from the break down of haemoglobin in the
liver.
• Bile salts: Emulsify the fats: they break them up into
small drops which are more easily digested by lipase.

24. INTESTINAL JUICES
• The epithelial cells of the villi produce
enzymes which complete the breakdown of:
- Maltose → glucose
- Peptides → aa
- Fats → fatty acid and glycerol
before they are absorbed.
By -Maltase
-Peptidase

25. FINAL PRODUCTS OF DIGESTION
FOOD FINAL PRODUCTS
Starch Glucose
Proteins Amino acids
Fats Fatty acids + glycerol

27. ABSORPTION: ILEUM

28. VILLI: Hystology

29. Structure of a villus

30. Molecules
Epithelial cells → a large proportion of
↓ fatty acid + glycerol
capillaries (bloodstream ) ↓
↓ form fats again
pass to lacteals
Hepatic Portal Vein ↓
↓ lymphatic system
LIVER
↓
General circulation (vena cava)

31. LARGE INTESTINE
Colon and rectum
• Material that reaches it contains:
i) water with undigested matter
ii) cellulose
iii) fibre: digested partly by bacteria
iv) mucus
v) dead cells from the lining of the alimentary canal
• Function: absorption of water.
semisolid waste → faeces → rectum → anus (EGESTION)

32. ASSIMILATION
• Glucose
Respiration energy
• Fats
-Are built into cell membranes and other cell structures
- Source of energy
• Amino acids
- Built up into proteins. Functions??

33. STORAGE OF DIGESTED FOOD
• Glucose
- Changed in the liver to glycogen
- Some of the glycogen is stored in liver
(short- term store) and muscles.
- LIVER: If ↓ blood sugars Glycogen → glucose → circulation
- MUSCLES: glucose: for muscular activity
- Excessof glucose: converted to fat and
stored in fats depots

34. STORAGE OF DIGESTED FOOD
• Fats
- There is no limit to storage of fats
- Long- term store as fat depots in:
-abdomen
- round the kidneys (adipose tissue)
- under the skin

35. STORAGE OF DIGESTED FOOD
• Amino acids
- They are not stored in the body
- Those not used in protein formation are
deaminated (in the liver)

36. DEAMINATION (in the liver)
aa
non nitrogen compound nitrogen compound
glucose UREA
respiration excreted by the kidneys
urine

37. LIVER
Functions
• Regulation of blood sugars.
• Production of bile.
• Deamination
• Storage of iron.
• Manufacture of plasma proteins.
• Detoxication.
• Storage of vitamins