657
CHAPTER SEVENTEEN
Digestive System
Palate
The
palate
(pal
at) forms the roof of the oral cavity and con-
sists of a hard anterior part and a soft posterior part. The
hard palate
is formed by the palatine processes of the maxil-
lary bones in front and the horizontal portions of the pala-
tine bones in back. The
soft palate
forms a muscular arch,
which extends posteriorly and downward as a cone-shaped
projection called the
uvula
(u
vu-lah).
During swallowing, muscles draw the soft palate and the
uvula upward. This action closes the opening between the
nasal cavity and the pharynx, preventing food from entering
the nasal cavity.
In the back of the mouth, on either side of the tongue and
closely associated with the palate, are masses of lymphatic
tissue called
palatine
(pal
ah-tı¯n)
tonsils
(F g. 17.7). These
structures lie beneath the epithelial lining of the mouth and,
like other lymphatic tissues, help protect the body against
infections (see chapter 16, p. 621).
Other masses of lymphatic tissue, called
pharyngeal
(fah-
rin
je-al)
tonsils,
or
adenoids,
are on the posterior wall of the
pharynx, above the border of the soft palate (F g. 17.7). If the
adenoids enlarge and block the passage between the nasal
cavity and pharynx, they may be surgically removed.
The palatine tonsils are common sites of infection and when
inF
amed, produce
tonsillitis.
Infected tonsils may swell so greatly that
they block the passageways of the pharynx and interfere with breath-
ing and swallowing. The mucous membranes of the pharynx, audi-
tory tubes, and middle ears are continuous, so such an infection can
spread from the throat into the middle ears (otitis media).
When tonsillitis occurs repeatedly and does not respond to anti-
biotic treatment, the tonsils may be surgically removed. Such tonsil-
lectomies are done less often today than they were a generation ago
because the tonsils’ role in immunity is now recognized.
The
lips
are highly mobile structures that surround the
mouth opening. They contain skeletal muscles and sensory
receptors useful in judging the temperature and texture of
foods. Their normal reddish color is due to the many blood
vessels near their surfaces. The external borders of the lips
mark the boundaries between the skin of the face and the
mucous membrane that lines the alimentary canal.
Tongue
The
tongue
(tung) is a thick, muscular organ that occu-
pies the fl oor of the mouth and nearly F lls the oral cavity
when the mouth is closed. Mucous membrane covers the
tongue, and a membranous fold called the
lingual frenulum
(ling
gwahl fren
u-lum) connects the midline of the tongue
to the fl
oor of the mouth.
The
body
of the tongue is largely composed of skeletal
muscle F
bers that run in several directions. These muscles
mix food particles with saliva during chewing and move
food toward the pharynx during swallowing. The tongue
also helps move food underneath the teeth for chewing. The
surface of the tongue has rough projections, called
papillae
(pah-pil
a)
(f g. 17.6)
. Some of these provide friction, which
helps handle food. Other papillae contain most of the taste
buds (see chapter 12, p. 448). Some taste buds are scattered
elsewhere in the mouth, particularly in children.
The posterior region, or
root,
of the tongue is anchored
to the hyoid bone. It is covered with rounded masses of lym-
phatic tissue called
lingual tonsils
(ton
silz)
(f
g. 17.7)
.
Uvula
Soft palate
Hard palate
Lip
Tongue
Vestibule
Lip
Palatine
tonsils
Lingual frenulum
FIGURE 17.5
The mouth is adapted for ingesting food and
preparing it for digestion, both mechanically and chemically.
Root
Body
Epiglottis
Lingual tonsils
Palatine tonsil
Papillae
FIGURE 17.6
The surface of the tongue, superior view.
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