| 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.
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