Figure 1317

Photomicrograph of aggregated nodules in the wall of the ileum.

This low-magnification photomicrograph provides an example of aggregated nodules. The multiple lymphatic nodules (indicated by a clashed line) with visible germinal centers are typically found in the ileum. This accumulation of lymphatic tissue is known as a Peyer's patch. The nodules originate in the lamina propria and extend into the submucosa of the ileum. x5.

As noted, diffuse lymphatic tissue and lymphatic nodules are named according to the region or organ in which they appear. In the alimentary canal they are collectively referred to as GALT; in the bronchial tree they are known as bronchus-associated lymphatic tissue (BALT). The term mucus-associated lymphatic tissue (MALT) includes GALT and BALT. Diffuse lymphatic tissue and lymphatic nodules of MALT are present in many other regions of the body (e.g., female reproductive tract) where the mucosa is exposed to the external environment. All lymphatic nodules become enlarged as a consequence of encounters with antigen.

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