When an individual needs food, he experiences the sensation of
is controlled by the h
s area of the brain, which receives i
various parts of the body for this purpose.
The process of food selection is related both to previous
g and to
As food enters the oral cavity, bite-size chunks of food are cut off by the upper
s. These chunks are about the right size for the
There are two key facts about digestion:
a. First, digestion is a
l process. Food is broken down into its
constituent parts through the process of
b. Second, this chemical process takes place only at
t surfaces of the food.
Food processes are broken down into smaller and smaller pieces through the
g. This greatly increases the total s
of the food. The grinding and crushing are accomplished by the p
teeth. Keeping the food between the surfaces of the grinding teeth are the
The fluids secreted into the oral cavity by the
y glands and the
glands are collectively known as
. These fluids serve to
t the surface areas
of the food particles. Saliva also d
s some of the molecules of food items.
These dissolved molecules are tested by the
s. Food particles are held
together as a bolus by the m
, which also makes the bolus somewhat slippery.
The bolus is moved posteriorly out of the
h into the p
then down through the
s to the stomach. Both the upper and lower air
passageways must be protected as the bolus passes through the
The actions of the tongue are produced by its
c muscles and the muscles
As the bolus approaches the pharynx, the upper air passageway is closed by the
e, which also t
s to resist the pressure from the bolus.