The Mouth

Here is a diagram of a vertical slice through your mouth. You should be able to label the diagram and explain what the various parts do.


A:  nasal cavity
B:  hard palate
C:  soft palate
D:  pharynx
E:  tongue
F:  epiglottis
G:  oesophagus (gullet)
H:  trachea (windpipe)
I:  salivary gland
J:  lower jaw
K:  mouth
L:  nostril

You normally breathe in and out through your nostrils and nasal cavity. You can even breathe in and out when you are chewing some food because the nasal cavity is separated from the buccal cavity (mouth cavity) by the palate.

The nasal cavity and the back of your mouth contain cells which can detect volatile chemicals. This is your sense of smell. When you have a bad cold and your nasal cavity is blocked up, you cannot taste your food properly. This is because what we experience as taste is really taste and smell put together.

The hard and soft palate are important because they allow you to breathe whilst you are chewing a mouthful of food. You know what it is like when you have a really bad cold: your nose is so blocked up that you have to breathe through your mouth. When you are chewing some food, you feel desperate for air and have to breathe through this mushy food.

The tongue helps us to talk; it is used to push food around the mouth and to the back of the mouth to swallow it. The tongue contains taste buds. The sensory receptors in the tongue can detect sweet, salt, acid (sour), and bitter tastes. What we call taste includes the smell of the food in our mouths.

To swallow food, it is pushed to the pharynx (back of the mouth) by the tongue. The epiglottis closes the entrance to the windpipe so that food does not go down the wrong way. It does sometimes: coughing forces the food back up the windpipe to unblock it. For a couple of seconds just before we swallow our food, the trachea is blocked by the epiglottis, so we cannot breathe.

The oesophagus has circular muscles which can contract (peristalsis) to force food down into the stomach. Food has to be slippery to make it easy to swallow. This is why our saliva contains mucin which is a slimy protein. See how many dry biscuits you can eat in a minute. After a few, you cannot swallow any more because there is not enough saliva to make them slippery.

The salivary gland produces saliva. This contains mucin and water to make the chewed up food slippery. It also contains an enzyme called salivary amylase which turns starch into a sugar called maltose. We do not chew our food long enough to complete the digestion of starch which is why the pancreas makes pancreatic amylase to finish the job.

Taste is very important:

Sweet and salty things are generally good to eat, but very salty things are not.

Sour things are not ready to eat. We learn that unripe fruits do not taste nice and learn to wait until they ripen. It is better for the plant if we wait until the seeds are ready to be dispersed before we eat the fruits.

Bitter fruits are not nice to eat. Many of them are poisonous. We learn not to eat these fruits and to leave them for other animals to disperse the seeds.