Table 3-2 .Principal digestive juices, source and action
the aid of digestive enzymes, into solutions and
simple compounds. Carbohydrates (starches and
sugars) change into simple sugars (glucose); fats
change into fatty acids; and proteins change into
In the mouth the TEETH mechanically break
up food into small particles before it is swallowed.
The salivary glandsparotid, submaxillary, and
sublingualsecrete saliva, which moistens the
food, makes it easier to chew, and lubricates the
food mass to aid in swallowing. About 1,500 ml
of saliva are secreted daily. Saliva contains one
principal enzyme, ptyalin, which initiates chemical
digestion of starches, breaking them into the com-
plex sugar maltose.
The TONGUE is a muscular organ attached
to the lower jaw at the back of the mouth and
is the chief organ of taste. It assists in mastica-
tion, swallowing, and speech.
The pharynx (see The Respiratory System) is
the passageway between the mouth and the
esophagus and is shared with the respiratory tract.
The EPIGLOTTIS is a cartilaginous flap that
closes the opening to the larynx when food is be-
ing swallowed down the pharynx. Food is de-
flected away from the trachea to prevent particle