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Oral Cavity

The oral cavity is specialized for sensory discrimination (taste), mechanical processing (chewing), initial lubrication and enzymatic digestion (salivary secretion), and immune surveillance (tonsils), with a protective stratified squamous epithelium throughout.

Clinically, the oral cavity provides an easy opportunity for revealing examination of a mucosal surface ("Please open your mouth and say AH").  

For an extreme example (candidiasis), see WebPath (gross image) and WebPath (micrograph).

The oral mucosa varies from site to site within the oral cavity, but everywhere the epithelium is protective stratified squamous.  This epithelium is partially keratinized on gums and hard palate and on filiform papillae of tongue; it is non-keratinized elsewhere.  Lamina propria is unspecialized.  A muscularis mucosae is not present.


Tongue

The mucosal surface of the tongue, the part you can see when the patient says, "AH", displays several specialized epithelial variations, including papillae of various shapes.  Variations in gross appearance can be clinically revealing. (For an extreme example, see WebPath, gross image, and WebPath, micrograph.)

In addition to its clinical value as a readily-observed "window" onto a mucosal surface, the tongue also provides excellent opportunities for learning histology, with examples of all the basic tissue types appearing in a variety forms.

The bulk of the tongue consists of striated muscle fibers arranged in bundles along three mutually perpendicular axes, so any plane section is likely to reveal fibers cut both transversely and longitudinally.  Bundles of myelinated nerve fibers are usually easy to find within the muscle of the tongue.

The surface of the tongue is covered by stratified squamous epithelium, modified on the upper surface into filiform papillae.  These papillae, which comprise the whitish "fuzz" over most of the lingual surface, have keratinized tips (hence the whitish color) and provide roughness which contributes to tongue's food-handling ability.  (The name filiform means file-like.  The resemblance to a file is obvious if you've ever felt a cat's tongue, which has these papillae heavily keratinized.)

Scattered among the filiform papillae are occasional fungiform papilla.  Taste buds are found on fungiform papillae.

The thumbnail shows foliate (leaf-shaped) papillae from rabbit tongue, which in section appear similar to human fungiform papillae.

Taste buds are oval clusters of elongated cells which extend across the thickness of the epithelium, from the lamina propria to the taste pore at the surface.  

Within a taste bud, each sensory cell has microvilli in the taste pore at its apical end.  These allow contact with the external medium.  At the basal end, each sensory cell makes synaptic contact with fibers of the facial nerve (CN VII) or glossopharyngeal nerve (CN IX).


Tonsils

Tonsils are lymphoid structures located in the mucosa of the tongue, palate, and pharynx which provide sites where immune surveillance cells (lymphocytes) can encounter foreign antigens enter the body through the mouth or nose.

Each tonsil consists of an epithelial crypt (invaginated pocket) surrounded by dense clusters of lymph nodules, each with a germinal center where lymphocytes proliferate.  The nodules are embedded in a mass of diffuse lymphoid tissue that consists of lymphocytes migrating to and from the germinal centers.

The epithelium lining the crypt corresponds with that on the adjacent surface -- stratified squamous in the tongue and palate, or pseudostratified columnar in the pharynx.  In either case, the epithelium may be heavily infiltrated with lymphocytes, and the crypt may be filled with lymphocytes and other debris.

The lymphoid tissue of the tonsils is similar to that of Peyer's patches and appendix. These structures, together with other more diffuse lymphoid tissue, constitute the Gut-Associated Lymphoid Tissues, or GALT.

For more on GALT (or, more generally, MALT for Mucosa-Associated Lymphoid Tissues), consult your histology text (e.g. pp. 134-5 in Stevens & Lowe).


Palate

The hard palate has a partially-keratinized epithelium, much of which is firmly attached by a fibrous submucosa to underlying bone.

The soft palate has a non-keratinized epithelium, with underlying minor salivary glands and striated muscle.  The largest tonsils (the palatine tonsils) are embedded in the sides of the soft palate.


Oral cavity examples:


Comments and questions: dgking@siu.edu

SIUC / School of Medicine / Anatomy / David King

http://www.siumed.edu/~dking2/erg/oralcav.htm
Last updated:  1 October 2012 / dgk