Maintenance of the Body
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.
is also called the
al). Its boundaries are the lips anteriorly, cheeks laterally, pal-
ate superiorly, and tongue inferiorly
. Its anterior
opening is the
. Posteriorly, the oral cavity is con-
tinuous with the
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
, which helps to explain how the mouth—a site teeming
with disease-causing microbes—remains so remarkably healthy.
The Lips and Cheeks
) and the
, 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
the ﬂeshy lips; the cheeks are formed largely by the
. Te recess bounded externally by the lips and cheeks and
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
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
(a) Sagittal section of the oral cavity and pharynx
(b) Anterior view
Anatomy of the oral cavity (mouth).