Structure and function of digestive system and enzymes

1. DIGESTION Chapter 3
(Biology)

2. The body carries out digestion of food to convert
large insoluble food molecules into smaller soluble
ones.
carbohydrate
molecule protein
molecule
fat
molecule
Small food molecules can pass through the walls of
the small intestine and then dissolve into the blood
stream. Large food molecules cannot do this.
WHAT IS DIGESTION?

3. THE BREAKDOWN OF FOOD
Physical
breakdown
Chemical
breakdown

4. PHYSICAL BREAKDOWN OF FOOD
- It starts in the mouth.
- Food is physically broken down from
large pieces into small pieces.
- The teeth play a major part in the
physical breakdown of food

5. 4 TYPES OF TEETH
Teeth Shape Function
Incisors Chisel
shaped
Biting into soft food
Canines Sharp and
pointed
Tearing into tough food
(meat)
Premolars Cups with
grooves
Form a crushing and
grinding surface
Molars Cups with
groves
Form a crushing and
grinding surface

6. - We have two sets of teeth.
Milk teeth Permanent teeth
- 20 teeth
- Emerge through the
gums at about 6
months of age.
- This set is complete
by about the age of 3
years.
- 32 teeth
- Replaces milk teeth.
- The replacement
starts at the age of 6
and is complete by the
age of 17.

7. CHEMICAL BREAKDOWN OF FOOD
- Carbohydrates, fats and
proteins are made from large
molecules (insoluble).
- When the molecules are
broken down into smaller
molecules they become
soluble and can pass
through the digestive

8. ENZYMES
- Enzymes are made
by the body from
proteins and they
speed up chemical
reactions.
- Almost ALL reactions
in living things
involve enzymes.

9. - Enzymes belong to a group of chemical
substance called CATALYSTS.
- CATALYSTS are substances that
speeds up chemical reactions without
being changed or used up in the
reaction.
- Digestive enzymes speed up the
breakdown of the large molecules into
smaller ones.

11. WHEN YOUR MOUTH WATERS
Sub
maxillary
- The water formed in your
mouth is called saliva.
- We can make 1.5 L of saliva in
24 hrs.
- Saliva is made by 3 pairs of
salivary glands (made up of
saliva secreting cells and
ducts).
- Saliva is 99% water.
- It also contains mucin (slimy
substance) and amylase (breaks

12. WHEN YOU SWALLOW
- When you have chewed your
food it is made into a pellet
called the bolus.
- The bolus is pushed to the back
of your mouth by the tongue.
- Swallowing causes the bolus to
slide down your gullet
(oesophagus).
- The oesophagus has 2 layers of
muscles:
(a) Outer layer------ Longitudinal

13. - In the gullet when the circular
muscles contract they push on
the food.
- Then the longitudinal muscles
contract to stretch (relax) the
circular muscles.
- Circular muscles do not all
contract at the same time.
- The wave of muscular
contraction is called peristalsis.
- Peristaltic waves occur in other
parts of the alimentary canal to
push the food.

14. After food is swallowed it enters the stomach, which is
basically a muscular bag filled with hydrochloric acid.
THE STOMACH
muscle
tissuefood leaves
the stomach
food enters
from the
gullet
Two things happen to food in the stomach:
 the chemical breakdown of food begins;
 microbes are destroyed.

15. - The stomach wall is lined with glands which secret
hydrochloric acid and a protein digesting enzyme called
pepsin (protease).
- The hydrochloric acid kills many bacteria in the food and
provides the pepsin with the pH conditions to work.
- The food is churned up by the action of the muscles as they
send peristaltic waves down the stomach wall (3
waves/min.)

16. - When food is broken down into a creamy liquid the valve
that stopped the food from leaving the stomach opens.
- This allows the food to pass to the next part of the digestive
system, the DUODENUM

17. THE DUODENUM, LIVER AND
PANCREAS
- The duodenum is
part of the small
intestine.
- It is connected to
the stomach.
- 2 tubes (ducts)
open into the
duodenum.

18. - The 2 tubes leading into the duodenum
are:
Bile duct Pancreatic ductFunction:
- Carries a green liquid
called bile from the
gall bladder.
- Bile is made in the
liver.
- It contains chemicals
that break down the
fat into small droplets
so that the fat-
digesting enzymes
can work easily.
Function:
- Produces a juice
containing enzymes
that digest proteins,
fats and
carbohydrates.

19. - The mixture of liquids from the stomach, liver and pancreas
pass on into the small intestine.

20. THE FATE OF UNDIGESTED FOOD
Sub
maxillary
- Indigestible parts of the food (ex.
Cellulose) pass on through the small
intestine to the large intestine.
- The 1st part of the large intestine is called
the caecum.
- This is attached to a much longer part
called the colon.
- Here water and some dissolved vitamins
are absorbed and taken into the body.
The remaining semi-solid substances
form the faeces.
- The faeces are removed from the body

21. ENZYMES SUMMARY
Region of
production
Type of
enzyme
Notes
Salivary glands in the
mouth
Carbohydrase Enzyme is called salivary
amylase
Gastric glands in
stomach
Protease - Enzyme is called pepsin
- Hydrochloric acid is
made to make the
enzyme work
Pancreas Protease,
Carbohydrase,
- Enzymes enter the
duodenum and mix with

22. EXCRETORY SYSTEM Biology

23. A CLOSER LOOK AT THE
EXCRETORY SYSTEM

24. - The wastes produced by the body collect in the blood.
- They are removed from the body by the excretory system.
- As the blood passes through the kidneys, a waste called
urea is filtered from the blood with some water.
- On a hot day, when the blood passes through the skin
carrying the water and the urea, they are released onto the
skin to cool the skin.
- As the blood passes through the lungs the carbon dioxide is
removed and passed into the air.