The mouth is where food first enters
the digestive system. The parts of the mouth are the lips and
cheeks, gums and teeth, tongue and salivary glands. Together they
take food and turn it into a liquid so that it can be swallowed and
sent to the stomach.
Lips and Cheeks
The lips form the entry to the mouth and join the
gums and cheek muscles. The outer surface of the lips is skin and
the inside is a mucus membrane. Lips get their red colour from the
network of blood vessels which are visible under the surface. The
cheeks are similar to the lips but have a large area of fat under
the surface of the skin. At the back of the mouth on the cheeks are
glands which release the mucous found in the mouth. Teeth and
Gums are mucous tissue which hold the teeth in place.
The gums have blood vessels at the base of the teeth, which give
the teeth nutrients. Teeth are used to hold, tear and chew food so
that it can be swallowed. Not all teeth are the same as they do
different jobs. Incisors are the front teeth and are used for
biting and cutting while our back teeth or molars are used for
grinding down our food.
When food first enters the mouth the tongue moves it
towards the molars so that it can be ground down. The tongue is a
muscle and has glands that secrete some of the saliva found in the
mouth. It is also covered in taste buds which can sense sweet,
sour, salty and bitter flavours in the food. The tongue then sends
signals to the brain and it is the combination of these four
flavours that give every piece of food its unique flavour. An
interesting function of the tongue is that its movement creates a
negative pressure in the mouth which lets mammals suckle milk from
As you eat teeth break food down into smaller pieces
which are then mixed with saliva. There are many small salivary
glands found on the tongue and cheek but there are also three main
pairs. The largest pair are 20-30 grams (0.7-1.0 ounce) while the
smallest are 2-3 grams (0.07-0.11 ounces). When your body becomes
dehydrated and there is not enough water in the bloodstream it is
taken from the salivary glands.
You become thirsty because the mouth is dry from lack
Saliva is slightly acidic with a pH of 6.7 and
dissolves foods so that they can be easily tasted and digested.
Saliva is 99% water and contains enzymes which chemically break
down the food into its different nutrients. The food then becomes a
tasteless watered down mixture so it can pass easily into the
stomach. The sight or smell of food can stimulate the nerves that
control the flow of saliva, with most people producing two to three
pints (0.9-1.4 litres) every day. Saliva can be watery and flow
very easily or thicker and flow slowly, depending on the type of
food being eaten. Sour foods need more saliva as they are harder to
break down, while foods that are already moist and in smaller
sections need less saliva.
The substance in saliva that chemically breaks down
the food is called ptyalin. When the saliva first comes in contact
with the food it breaks down the complex starches into simpler
ones. Even when the food reaches the stomach the ptyalin is still
acting on the food and making it more digestible.