Digestion Begins in the Mouth
Digestion begins when you bring food into your mouth
(ingestion). The jaw muscles and teeth help you chew
(masticate) your food, as shown in Figure 14.3. Chewing
physically breaks the food into smaller pieces, which in-
creases the surface area of your waffles, sausages, and eggs
that is available for subsequent chemical digestion. Vari-
ous teeth are specialized for the different ways in which
they break apart food (tearing off chunks of sausage, cut-
ting up eggs and waffles, grinding the sausage into bits
that can be swallowed). Salivary glands secrete fluid called
sa liva
through ducts that lead into the mouth. Saliva mixes
with the food pieces, lubricates and moistens the food,
kills bacteria, and begins to digest starches in your meal.
Movements of your tongue move the food to contact the
teeth and help shape the chewed food into a soft, rounded,
flexible mass called a bolus.
I n g e s t i o n o f f o o d
F ig u r e 1 4 . 3
The mouth receives the food. The mouth is defined by the hard and soft
palates, the tongue, and the cheeks. The teeth and salivary glands are also
associated with the mouth.
Incisors
cut food
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GEOGRAPHIC
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Hard palate
(bony)
forms most of the
Enamel
(made of
calcium salts) protects
the tooth from wear
and tear.
Dentin
(calcified
connective tissue)
makes up the majority
of the tooth.
Pulp cavity
contains
pulp (connective tissue
containing nerves and
blood vessels).
Root
canal
is a
channel for nerves and
blood vessels.
Submandibular
gland
Periodontal ligament
helps anchor the tooth
to the underlying bone.
The three major
salivary glands
are the parotid gland, submandibular
gland, and sublingual gland. They secrete
saliva
, which consists
mainly of water (99.5%) and solutes, including:
Salivary amylase
—Enzyme that begins digestion of starch
Mucus
—Lubricates food
Lysozyme
—Enzyme that kills bacteria
Sagittal section of a molar
roof of the mouth.
S oft palate
(muscular) forms
the rest of the
mouth’s roof.
Uvula
prevents -
swallowed food
from entering the
nasal cavity.
Molars
grind
food.
Cuspids (canines)
tear food.
Parotid duct
Parotid gland
Gums (gingiva)
cover
tooth sockets and help
to anchor teeth.
Tongue
forms the floor of the
mouth, manipulates food for
chewing and swallowing,
shapes food, and senses taste.
Premolars
crush
and grind food.
Crown
Neck
Sublingual
gland
Root
Lingual frenulum
limits
movement of the tongue
posteriorly.
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