Digestion & Enzymes
Stages of Nutrition
1.
2.
3.
4.
5.
Ingestion
Digestion
Absorption
Assimilation
Egestion
1. Ingestion – Taking food into the mouth.
2. Digestion – The break down of food by teeth in the
mouth and by chemicals in the stomach and small
intestine.
3. Absorption – the movement of digested food from
the small intestine into the blood.
4. Assimilation – the use of food by body cells for
energy, growth and repair.
5. Egestion – the release of undigested food from the
body.
1. The Mouth!
There are two types of digestion
• Chemical
• Physical (Mechanical)
http://www.medtropolis.com/vb
ody.asp
1. Incisors – biting.
2. Canines – tearing.
3. Premolars – chewing.
4. Molars – grinding
An Enzyme is a catalyst, made in the
body, which speeds up a reaction
without itself being used up in the
reaction.
The ENZYME works on a SUBSTRATE
to make a PRODUCT
Enzymes
•Big food molecules can’t pass through cell
walls.
•ENZYMES are used to break up big
molecules into small ones
•These small molecules can pass through
the wall of the small intestine into the
blood. They then pass into cells and are
used.
Gut
Blood
Food is absorbed
in the small
intestine. The
wall of the gut
has lots of tiny
holes in it.
Small molecules
such as glucose
can pass into the
blood but large
molecules such
as starch are left
in the gut.
Play animation
NCE-MSTL
BUT large molecules can be broken
down into small molecules by
enzymes.
Enzymes are special proteins that act
as biological catalysts. They speed up
chemical reactions in the body.
Digestive enzymes work by fixing onto
the food molecule or substrate and
breaking it into smaller molecules.
NCE-MSTL
Each enzyme fits
onto a specific
substrate
ENZYME
For example,
amylase enzymes
break down starch
SUBSTRATE
Play animation
NCE-MSTL
So…
AMYLASE enzymes
break down
STARCH (CARBOHYDRATE)
into
MALTOSE.
NCE-MSTL
• Enzyme=
• Substrate=
• Product=
Gut
Blood
Play animation
NCE-MSTL
These digestive
enzymes allow
food to be
broken into
small enough
molecules to be
absorbed from
the gut into the
blood.
BUT large particles can be
broken down into small particles.
This is called DIGESTION
The Oesophagus
• The food is pushed down the
oesophagus to the stomach by a wave
of muscular action called peristalsis.
The Stomach
Muscular bag that holds 2 litres of food.
Secretes hydrochloric acid.
Makes digestive juices.
Muscular walls churn the food making sure it’s all
mixed.
• After 2-3 hours churning it’s a runny liquid called
chyme.
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The Small Intestine
• Actually 6 m long!
• Plays important roles in
digestion and absorption
• Two important liquids
are added here:
Pancreatic juices
Bile
Absorption
• Digested food has to pass into the blood
through the small intestine wall.
• Well designed – thin lining, good blood supply
and a VERY LARGE surface area.
• It has a folded inner lining, millions of tiny
villi
Pancreas
• Produces digestive
enzymes
• E.g. amylase
Liver
• After food has been
absorbed into the blood,
the food is taken to the
liver.
• The liver processes
some of it, before it
goes any further.
• The food dissolved in
plasma is the taken to
other parts of the body.
The Large Intestine.
• Mainly fibre, dead cell,
bacteria and water
reach here!
• As it moves along here
most of the water is
absorbed into the blood.
• Faeces are stored in the
rectum.
• Eventually egested out
of the anus, roughly 24
–48 hours after eating.
Experiment write up
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Questions:
What did you use to test for starch?
What colour showed that starch was present?
What colour showed that starch was not present?
What was the substrate in this experiment?
What was the product in this experiment?
Was this a fair test?
Explain your answer.
Where in the body is amylase found?
Why did we use the waterbath at 37.5’C?
• http://videos.howstuffworks.com/discovery/2
8649-assignment-discovery-breaking-downdigestion-video.htm
• http://videos.howstuffworks.com/discoveryhealth/14062-body-invaders-digestiveproblems-video.htm
• http://www.insidestory.iop.org/insidestory_fl
ash1.html