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.