Figure 1315

Photomicrograph of a lymph node. This photomicrograph shows the superficial cortex (SC), deep cortex (DC), and medulla (M) of the lymph node in a routine H&E preparation. The capsule (Cap) is composed of dense connective tissue from which trabeculae (T) penetrate into the organ. Below the capsule is the subcapsular sinus (SCS). It receives lymph from afferent lymphatic vessels that penetrate the capsule. The subcapsular sinus is continuous with the trabecular sinuses that course along the trabeculae. The superficial cortex contains the lymphatic nodules (LN). The deep cortex is nodule free. It consists of densely packed lymphocytes and contains the unique high endothelial venules (not visible at this magnification). The medulla consists of narrow strands of anastomosing lymphatic tissue called medullary cords (MC), separated by light-appearing spaces, the medullary sinuses (MS). The medullary sinuses receive lymph from the trabecular sinuses as well as lymph that has filtered through the cortical tissue. x140.

• A mantle zone or corona, which represents an outer ring of small lymphocytes that encircles the germinal center.

Lymphatic nodules are usually found in structures associated with the alimentary canal such as the tonsils, ileum, and vermiform appendix

Generally, nodules are dispersed singly in a random manner. In the alimentary canal, however, some aggrega-

tions of nodules are found in specific locations. These include

• Tonsils, which form a ring of lymphatic tissue at the entrance of the oropharynx. The pharyngeal tonsils, or adenoids, located in the roof of the pharynx; the palatine tonsils, or simply the tonsils, on either side of the pharynx, between the palatopharyngeal and palatoglossal arches; and the lingual tonsils, at the base of the tongue, all contain aggregates of lymphatic nodules. The palatine tonsils consist of dense accumulations of lymphatic tissue located in the mucous membrane. The squamous epithelium that forms the surface of the tonsil dips into the underlying connective tissue in numerous places, forming tonsillar crypts (Fig. 13.16). The walls of these crypts usually possess numerous lymphatic nodules. Like other aggregations of lymph nod-

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