Download File - Sanders School

Bile
LQ: What does it do?
Learning outcomes
• All: must give the two uses of bile
• Most: can explain what bile does to lipids
• Some: can explain how bile increases the
surface area of lipids
• Grade 6: explain how surface area increases
digestion and explain the terms emulsification
micelle and increased digestion
Why do we chew our food?
• Chewing breaks up large chunks of
food into smaller chunks
• Chewing mixes in saliva…
• … which contains amylase.
• Amylase is an enzyme which breaks
down starch into simple sugars.
Amylase
Starch
molecule
Sugars
(maltose)
• Solid lumps of food can only be digested from the outside
• If we break large lumps of food down into smaller pieces…
Lump of food
Chewing
Enzymes
• … we increase the surface area for
the enzymes to work on
• This will speed up the rate of chemical digestion by the
enzymes
Progress check
1.
2.
3.
4.
What is the function of the teeth?
What enzyme is produced in the mouth?
What is the purpose of chewing your food?
How does this help amylase do its job?
The Stomach
• The stomach is a muscular bag which mashes
food into a watery paste called chyme
• The lining of the stomach
produces gastric juice
• Gastric juice contains:
- water
- hydrochloric acid
which kills microbes in
the food and provides
the optimum pH for…
- pepsin, an enzyme which
breaks down proteins into
amino acids
Pepsin &
Hydrochloric
Acid
Progress check
1. What does pepsin break down?
2. What does the stomach lining produce?
3. What two functions does hydrochloric acid
have in the gut?
4. What is the protein broken down into?
Pepsin
Amino acids
Protein
molecule
The Small Intestine
Once the stomach has
reduced the food to a
smooth paste, it passes
into the small intestine
• The lining of the small
intestine produces
enzymes
• More enzymes are added
by the pancreas
The enzymes in the small
intestine have an optimum
pH of 6 - 8
Why is this a problem?
Pancreas
Digestive
Enzymes
Pepsin &
Hydrochloric
Acid
Liver
Gall
Bladder
Pancreas
Sodium bicarbonate
Bile
 The pancreas produces
sodium bicarbonate
 The liver produces bile
salts…
 … which are stored in the
gall bladder until they are
needed
 Sodium bicarbonate and bile salts are
alkali…
 … so they neutralize the stomach acid
Progress check
1. Why are bile and sodium bicarbonate added
to the small intestine?
2. What happens to the digested food in the
small intestine?
Fat
molecule
Lipase
Fatty acids
 The contents of the small intestine are
mostly water
 Digestive enzymes are water soluble,
but…
 … fats do not dissolve in water, so…
 … lipases can only digest fats at the
surface of fat droplets
Lipase
enzyme
particles
Fat
(e.g. Vegetable
oil)
Surface where
fat and water
meet
Water
 Adding bile salts cause fats to emulsify in water (emulsify-to
become an emulsion, two liquids mixed together)
Micelle
Add bile
Shake
Water
Emulsion
 The fat forms tiny droplets called micelles which will stay
suspended in water and not separate out
 This massively increases the surface area for the lipase enzymes
to work on
Progress check
1. Why does the lipid have to be made into
smaller pieces before it can be digested?
2. What is the term that describes the breaking
down of lipids? (think “e”)
3. What is a small piece of lipid called?
4. What does this process increase? (think “s”
“a”)
Bile 6 mk Q answer
1. Emulsifier – means to make two liquids mix
together e.g. oil and water
2. Bile acts upon fats
3. Bile is produced in the liver and stored in the
gall bladder
4. Increases surface areas of fat droplets so it
can be digested easier by enzymes
5. Lipase enzyme digests the fat into fatty acids
and glycerol