856
UNIT 4
Maintenance of the Body
23
chew food and mix it with saliva containing enzymes that begin
the process of digestion. Te mouth also begins the propulsive
process of swallowing, which carries food through the pharynx
and esophagus to the stomach.
The Mouth
Te
mouth
is also called the
oral cavity
, or
buccal cavity
(buk
9
al). Its boundaries are the lips anteriorly, cheeks laterally, pal-
ate superiorly, and tongue inferiorly
(Figure 23.7)
. Its anterior
opening is the
oral orifice
. Posteriorly, the oral cavity is con-
tinuous with the
oropharynx
.
Te walls of the mouth are lined with a thick stratified squa-
mous epithelium (see Figure 4.3e) which withstands considerable
friction. Te epithelium on the gums, hard palate, and dorsum of
the tongue is slightly keratinized for extra protection against abra-
sion during eating. Like all moist surface linings, the oral mucosa
responds to injury by producing antimicrobial peptides called
de-
fensins
, which helps to explain how the mouth—a site teeming
with disease-causing microbes—remains so remarkably healthy.
The Lips and Cheeks
Te
lips
(
labia
) and the
cheeks
, which help keep food between
the teeth when we chew, are composed of a core of skeletal mus-
cle covered externally by skin. Te
orbicularis oris muscle
forms
the fleshy lips; the cheeks are formed largely by the
buccina-
tors
. Te recess bounded externally by the lips and cheeks and
PART 2
Functional Anatomy
of the Digestive System
Now that we have summarized some points that unify the di-
gestive system organs, let’s consider the special structural and
functional capabilities of each organ of this system. Figure 23.1
shows most of these organs in their normal body positions, so
you may find it helpful to refer back to that illustration from
time to time as you read the following sections.
The Mouth and Associated
Organs
Describe the gross and microscopic anatomy and the basic
functions of the mouth, pharynx, and esophagus.
Describe the composition and functions of saliva, and
explain how salivation is regulated.
Explain the dental formula and differentiate clearly
between deciduous and permanent teeth.
Te mouth is the only part of the alimentary canal involved in
ingestion. However, most digestive functions associated with
the mouth reflect the activity of the related accessory organs,
such as teeth, salivary glands, and tongue. In the mouth we
Uvula
Uvula
Soft palate
Palatoglossal arch
Palatine
tonsil
Palatine
tonsil
Sublingual
fold with
openings of
sublingual ducts
Hard palate
Oral cavity
Tongue
Tongue
Upper lip
Lower lip
Oral vestibule
Gingivae (gums)
Gingivae
(gums)
Hard palate
Soft palate
Lingual frenulum
Opening of
Submandibular
duct
Palatine
raphe
Inferior labial
frenulum
Lingual tonsil
Oropharynx
Posterior wall
of oropharynx
Palatopharyngeal
arch
Superior labial
frenulum
Palatoglossal
arch
Epiglottis
Hyoid bone
Laryngopharynx
Esophagus
Trachea
(a) Sagittal section of the oral cavity and pharynx
(b) Anterior view
Figure 23.7
Anatomy of the oral cavity (mouth).
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