The Mouth
The mouth performs two functions:
1. Mechanical digestion
involves chewing – teeth chop and
grind food into small pieces.
2. Mixing food with saliva
saliva starts the break down of
carbohydrates (starch) using an
enzyme called amylase.
Amylase
The Oesophagus
After being swallowed
the food travels down
the oesophagus.
The Stomach
O
The stomach continues to mix the
food with digestive enzymes.
Amylase continues to digest
carbohydrates
Proteins are digested in
the stomach and small intestine.
Protease enzymes break down
proteins into amino acids.
Digestion of proteins in the
stomach is helped by stomach
acid, which is strong hydrochloric
acid. This also kills harmful microorganisms that may be in the food.
Protease
Small Intestine Lipase enzymes break down fat
into fatty acids and glycerol.
Digestion of fat in the small
intestine is helped by bile, made
in the liver. Bile breaks the fat
into small droplets that are
easier for the lipase enzymes to
work on.
Lipase
The Small Intestine- Microvilli
The inside of the intestine is folded and covered in
microvilli. The microvilli increase the surface
area of the intestine to increase the absorption
of carbohydrates, amino acids and fats
Large Intestine
By the time food reaches
the large intestine all
useful nutrients have
been absorbed into the
blood. All that remains
are waste products of
digestion and water.
The water is very valuable
so is absorbed into the
blood stream
The appendix is used to help
some animals digest cellulose in
plants. In humans the appendix
has a very limited role as
humans do not need to digest
cellulose for carbohydrates.
Waste products pass
through the large
intestine to be stored in
the rectum before
passing out of the anus as
faeces.
Liver and Pancreas
The liver and the
pancreas play
important part in
digestion. The liver
produces bile, which
helps the digestion of
fat.
The pancreas produces
chemicals called digestive
enzymes such as:
• Protease - proteins
• Carbohydrase (amylase)
- carbohydrates
• Lipase - fats