Plate 32 Tonsil

The palatine tonsils (faueial tonsils) are paired, ovoid structures that consist of dense accumulations of lymphatic tissue located in the mucous membrane of the fauces (the junction of the oropharynx and oral cavity). This low-magnification (X30) survey micrograph shows the general structural features of part of the human tonsil. The epithelium that forms the surface of the tonsil dips into the underlying connective tissue in numerous places, forming crypts known as tonsillar crypts. One of these crypts is seen in the survey micrograph (arrows). Numerous lymphatic nodules are evident in the walls of the crypts.

In addition to the palatine tonsils illustrated here, similar aggregations of lymphatic tissue are present beneath the epithelium of the tongue (lingual tonsils), under the epithelium of the roof of the nasopharynx (pharyngeal tonsils), and in smaller accumulations around the openings of the auditory (Eustachian) tubes.

The tonsils guard the opening of the pharynx, the common entry to the respiratory and digestive tracts. They can become inflamed because of repeated infection in the oropharynx and nasopharynx and can even harbor bacteria that cause repeated infections if they are overwhelmed. When this occurs, the inflamed palatine tonsils and pharyngeal tonsils (also called adenoids) are removed surgically (tonsillectomy and ade-noidectomy).

Figure 1, tonsil, human, H&E x180.

This shows, at a higher magnification, part of the same crypt as in the survey micrograph, as well as the adjacent epithelium (Ep) and one of the lymphatic nodules (LN). The crypt contains some cellular debris, a frequent occurrence. The lymphatic nodule exhibits a germinal center, the lighter central region of the nodule. The darker-staining peripheral portion of the nodule contains numerous, closely packed small lymphocytes intimately related to the epithelium; they have actually become incorporated in the epithelium. Portions of the germinal center have also become incorporated into the epithelium.

Figure 2, tonsil, human, H&E x400; inset x800.

The rectangular area in Figure 1 is shown here at higher magnification, rotated 90° counterclockwise. The stratified squamous epithelium (Ep) is just barely recognized because of the heavy infiltration of lymphocytes, with the deepest portion of the epithelium totally obscured, hence the question mark on the lead line. Epithelial cells are pres ent, though difficult to identify, in the germinal center as well as in the periphery of the nodule (small arrows). The inset shows the oval inscribed area at higher magnification and the epithelial cells (arrows) more clearly. In effect, this nodule has literally grown into the epithelium, distorting it and resulting in the disappearance of the well-defined epithelial-connective tissue boundary.

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