Figure 1316

Photomicrograph of a palatine tonsil, a. This low-magnification photomicrograph shows a H&E-stained palatine tonsil. The stratified squamous epithelium that forms the surface of the tonsil dips into the underlying connective tissue in numerous places, forming tonsillar crypts. x25. b. This higher-magnification photomicrograph of the rectangular area in a shows the stratified squamous epithelium (SSE) lining the tonsillar crypt. In the portion of the photomicrograph below the lumen of the crypt, SSE is well defined and separated by a coll ides, tonsils do not possess afferent lymphatic vessels; however lymph drains from the lymphatic tissue of the tonsil via efferent lymphatic vessels.

• Peyer's patches, which are located in the ileum (distal portion of the small intestine). They consist of numerous aggregations of lymphatic nodules containing T and B lymphocytes (Fig. 13.17). In addition, numerous, isolated single (solitaiy) lymph nodules are located along both large and small intestines.

• Vermiform appendix, which arises from the cecum. The lamina propria is heavily infiltrated with lymphocytes and contains numerous lymphatic nodules. Although the appendix is often described as a vestigial organ, the abundant lymphatic tissue that it contains during early life suggests that it is functionally associated with bursa-equivalent organs. With age, the amount of lymphatic tissue within the organ regresses and is difficult to recognize.

nective tissue layer (CT) from the lymphatic nodule (LN). In the upper portion of the photomicrograph, the SSE is just barely recognized because of the heavy infiltration of lymphocytes; the epithelial cells are present, however, although they are difficult to identify. In effect, the lymphatic nodule has literally grown into the epithelium, distorting it and resulting in the disappearance of the more typical, well-defined epithelial-connective tissue boundary. X450.

nective tissue layer (CT) from the lymphatic nodule (LN). In the upper portion of the photomicrograph, the SSE is just barely recognized because of the heavy infiltration of lymphocytes; the epithelial cells are present, however, although they are difficult to identify. In effect, the lymphatic nodule has literally grown into the epithelium, distorting it and resulting in the disappearance of the more typical, well-defined epithelial-connective tissue boundary. X450.

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