Chapter 23
The Digestive System
857
23
Te superior tongue surface bears papillae, peglike projec-
tions of the underlying mucosa
(Figure 23.8)
. Te conical
filiform papillae
roughen the tongue surface, helping us lick
semisolid foods (such as ice cream) and providing friction for
manipulating foods. Tese papillae, the smallest and most nu-
merous type, align in parallel rows on the tongue dorsum. Tey
contain keratin, which stiffens them and gives the tongue its
whitish appearance. Te mushroom-shaped
fungiform papil-
lae
are scattered widely over the tongue surface. Each has a vas-
cular core that gives it a reddish hue. ±en to twelve large
vallate
papillae
are located in a V-shaped row at the back of the tongue.
Tey resemble the fungiform papillae but have an additional
surrounding furrow. Pleatlike
foliate papillae
are located on the
lateral aspects of the posterior tongue.
Te fungiform, vallate, and foliate papillae house taste buds,
but those on the foliate papillae function in taste primarily in
infancy and early childhood. Serous cells just beneath the foliate
and vallate papillae secrete
lingual lipase,
a fat-digesting enzyme
that operates in the acid environment of the stomach.
Immediately posterior to the vallate papillae is the
terminal
sulcus
, a groove that distinguishes the portion of the tongue
that lies in the oral cavity (its body) from its posterior portion in
the oropharynx (its root). Te mucosa covering the root of the
tongue lacks papillae, but it is still bumpy because of the nodular
lingual tonsil
, which lies just deep to its mucosa (Figure 23.8).
Check Your Understanding
11.
How does the oral vestibule differ from the oral cavity proper?
12.
Which structure forms the roof of the mouth?
13.
Besides preparing food for swallowing, the tongue has
another role. What is it?
For answers, see Appendix H.
internally by the gums and teeth is the
oral vestibule
(“porch”).
Te area that lies within the teeth and gums is the
oral cavity
proper.
Te
labial frenulum
(fren
9
u-lum) is a median fold that
joins the internal aspect of each lip to the gum (Figure 23.7b).
The Palate
Te
palate
, forming the roof of the mouth, has two distinct
parts: the hard palate anteriorly and the so² palate posteriorly
(Figure 23.7). Te
hard palate
is underlain by the palatine bones
and the palatine processes of the maxillae, and it forms a rigid
surface against which the tongue forces food during chewing.
Te mucosa on either side of its
raphe
(ra
9
fe), a midline ridge, is
slightly corrugated, which helps create friction.
Te
soF palate
is a mobile fold formed mostly of skeletal muscle
that rises reflexively to close off the nasopharynx when we swallow.
±o demonstrate this action, try to breathe and swallow at the
same time.
Laterally, the so² palate is anchored to the tongue by the
pal-
atoglossal arches
and to the wall of the oropharynx by the more
posterior
palatopharyngeal arches
. Tese two paired folds
form the boundaries of the
fauces
(faw
9
sēz;
fauc
5
throat), the
arched area of the oropharynx that contains the palatine tonsils.
Projecting downward from the free edge of the so² palate is the
fingerlike
uvula
(u
9
vu-lah).
The Tongue
Te
tongue
occupies the floor of the mouth (Figure 23.7). Te
tongue is composed of interlacing bundles of skeletal muscle
fibers, and during chewing, it grips the food and constantly
repositions it between the teeth. Te tongue also mixes food
with saliva forming it into a compact mass called a
bolus
(bo
9
lus; “a lump”), and then initiates swallowing by pushing the bo-
lus posteriorly into the pharynx. Te versatile tongue also helps
us form consonants (k, d, t, and so on) when we speak.
Te tongue has both intrinsic and extrinsic skeletal muscle
fibers. Te
intrinsic muscles
are confined in the tongue and are
not attached to bone. Teir muscle fibers, which run in several
different planes, allow the tongue to change its shape (but not
its position), becoming thicker, thinner, longer, or shorter as
needed for speech and swallowing.
Te
extrinsic muscles
extend to the tongue from their points
of origin on bones of the skull or the so² palate, as described in
Chapter 10 (see ±able 10.2 and Figure 10.8). Te extrinsic muscles
alter the tongue’s position. Tey protrude it, retract it, and move
it from side to side. Te tongue has a median septum of connec-
tive tissue, and each half contains identical muscle groups. A fold
of mucosa called the
lingual frenulum
secures the tongue to the
floor of the mouth and limits its posterior movements.
Homeostatic Imbalance
23.2
Children born with an extremely short lingual frenulum are o²en
referred to as “tongue-tied” because restricted tongue movement
distorts speech. Tis congenital condition, called
ankyloglossia
(“fused tongue”), is corrected surgically by snipping the frenulum.
Epiglottis
Palatopharyngeal
arch
Palatine tonsil
Lingual tonsil
Palatoglossal
arch
Foliate papillae
Vallate papilla
Terminal sulcus
Dorsum of tongue
Medial sulcus
of the tongue
Filiform papilla
Fungiform papilla
Figure 23.8
Dorsal surface of the tongue, and the tonsils.
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