258
UNIT 3
Organ Systems
glands and is attached to the underlying muscle. The lining
mucosa covers the inner oral surfaces of the lips, cheeks, soft
palate, the inferior surface of the tongue, and the fl
oor of the
mouth. This type of mucosa is less exposed to abrasion than
the masticatory mucosa. The lining mucosa provides a bar-
rier against the invasion of pathogens and toxic chemicals,
contains receptors for sensations, and serves immunological
functions. The lining mucosa also provides lubrication and
buffering by minor glands in the submucosal layer. Examples
of the lining mucosa include the lip (Fig. 14-2D) and cheek
(Fig. 14-3A).
MASTICATORY MUCOSA
is covered by
keratinized strati-
f
ed squamous epithelium
, which is exposed to signi± cant abra-
sion due to high compression and friction during chewing.
The epithelium of the masticatory mucosa is composed of the
stratum basale
,
stratum spinosum
,
stratum granulosum
, and
stratum corneum
. It has a thick
lamina propria
that contains a
dense network of collagen ± bers and a few elastic ±
bers. This
layer has no submucosa and is directly and ± rmly attached to
the underlying bone. Masticatory mucosa can be found cover-
ing the oral surfaces of the gingiva and the hard palate. Injec-
tion into this area is dif± cult and painful because of its sensitive
periosteum, high collagen density, and ± rm attachment to the
bone. See Figure 14-4A for examples of the gingiva and Figure
14-4B for the hard palate.
SPECIALIZED MUCOSA
covers the anterior two thirds of
the tongue and consists of keratinized and nonkeratinized
squamous epithelium and numerous papillae. These papillae
can be classi±
ed into four types:
f
liForm
,
FungiForm
,
circum-
vallate
, and
Foliate papillae
. Most of these papillae have taste
buds. The
f
liForm papillae
are the only papillae without taste
buds; their main function is to aid in mixing food during chew-
ing. The lamina propria (connective tissue) of the specialized
mucosa is attached to the underlying skeletal muscle. These
muscles produce voluntary movement of the tongue and are
innervated by the hypoglossal nerve (cranial nerve [CN] XII).
Lining mucosa covers the inferior surface of the tongue. The
mucosa of the tongue is divided into two parts by a V-shaped
groove called the
sulcus terminalis
. The anterior two thirds of
the tongue is referred to as the
body oF the tongue
. Its mucosa
is innervated by the facial nerve (CN VII) and the trigeminal
nerve (CN V). The posterior third of the tongue is the
base oF
the tongue
. Its taste buds and mucosa are innervated by the
glossopharyngeal nerve (CN IX). The posterior third of the
tongue contains the lingual tonsils (Fig. 14-5A).
1.
Filiform papillae
are the smallest and most numerous of the
four types of papillae. They cover almost the entire supe-
rior surface of the anterior two thirds of the tongue and
are packed in rows that parallel the sulcus terminalis. Each
of the papillae appears cone shaped with some branching
processes. Connective tissue forms the central core of each
papilla. Filiform papillae have no taste buds and extend
from the nonkeratinized strati±
ed squamous epithelium.
The surface of the papilla is keratinized and is exposed to a
great deal of abrasion (Fig. 14-5B).
2.
Fungiform papillae
are less numerous than the ±
liform
papillae. They are mushroom shaped and are scattered
among the ±
liform papillae (Fig. 14-5C). Fungiform papil-
lae are located at the tip and on the two lateral edges of the
tongue. They are more numerous near the tip of the tongue.
Taste buds are found on the apical
surfaces of fungiform
papillae.
3.
Circumvallate papillae
are large and round with a fl
at-
topped cylindrical structure. There are about 10 to 14
papillae arranged in a row along the sulcus terminalis. Each
papilla is surrounded by a deep groove (moat), which forms
a valley around the papilla. Taste buds are found in the lat-
eral walls of each papilla (Fig. 14-6A).
4.
Foliate papillae
are leafl
ike folds with fl
at tops and have deep
clefts between the papillae. They are located on the
posterior
lateral surface of the tongue. They are more prominent in
some animals (such as rabbits) than in humans. Foliate
papillae contain taste buds in the lateral walls of the papillae
(Fig. 14-6B).
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