Histology of Mouth
and Pharynx
The mouth and pharynx are lined by a mucous membrane that is attached in
much of the area to the supporting wall (bone, cartilage, or skeletal muscle)
by a fibroelastic, gland-containing submucosa that varies greatly in size,
looseness, and the distinctness with which it can be delimited from the mucous
membrane. The submucosa is interpreted as absent on most of the hard palate,
the gums, and the dorsum of the tongue. The mucous membrane is composed of
epithelium, which is predominantly nonkeratinized, stratified, and squamous in
type, a basement membrane, and the fibroelastic lamina propria, which has
vascular papillae indenting the epithelium to varying degrees in different
areas. The muscularis mucosae, which is present in the digestive tube in
general, is missing in the mouth and pharynx. Its place is occupied by an
elastic network in the pharynx.
The lip has a framework of
skeletal muscle, chiefly the orbicularis oris muscle. External to this
are typical subcutaneous tissue and skin with hair follicles, sebaceous glands,
and eccrine sweat glands. On the inner side of the muscular framework is the
submucosa containing rounded groups of mixed, predominantly mucous glands (labial
glands). The submucosa is not definitely delimited from the covering
mucous membrane, which is composed, as described above, of lamina propria and
nonkeratinized, stratified, squamous epithelium. The free margin of the
lip has its characteristic red (or vermillion) color because the epithelial
cells contain much translucent eleidin, and the vascular papillae of the tunica
propria indent the epithelium more deeply here. The blood in the capillaries
thus shows through to a greater extent.
The general structure of the cheek is
very similar to that of the lip, the muscular framework being formed by the
buccinator muscle. Here some glands are external to the muscular framework. In
most of the lip and the cheek, the mucous membrane is quite closely bound to
the muscular framework, preventing large folds of mucous membrane from being
formed that might be easily bitten. Near the continuity of the mucous membrane
with the gums, the attachment is much looser to allow for freedom of movement.
The soft palate has a
fibromuscular framework, with the fibrous constituents (the expansion of the
tendons of the tensor veli palatini muscles) being more prominent near the hard
palate. On each side of the framework is a mucous membrane. That on the oral
side has an elastic layer separating the lamina propria from a much thicker
submucosa containing many glands. The epithelium is the typical
nonkeratinized, stratified, squamous variety, which rounds the free
margin of the soft palate and exten s for a variable distance onto the
pharyngeal surface.
The wall of the pharynx is for
the most part composed of a mucous membrane, muscular layer, and thin fibrous
sheath outside of the muscle that attaches the pharynx to adjacent structures.
The epithelium in the nasopharynx (except for its lowest portion) is
pseudostratified, ciliated, and columnar, whereas that of the rest of the
pharynx is nonkeratinized, stratified, and squamous. The lamina
propria is fibroelastic, with scattered small papillae indenting the
epithelium. The deepest part of this lamina is a definite elastic tissue layer with many longitudinally
oriented fibers. A well-developed submucosa is present only in the lateral
extent of the nasopharynx and near the continuity of the pharynx with the esophagus.
Scattered seromucous glands are present, mostly where there is
pseudostratified columnar epithelium. The muscular layer, made up of skeletal
muscle, is present as somewhat irregularly arranged layers.
