
Overview: Outer defense - Lymphoid nodules
Lymphoid nodules, more discrete aggregations of lymphoid tissue, are also located in the lamina propria of the GI, respiratory and urogenital systems. As such, they filter tissue fluid and are part of MALT. The illustration on the left shows a nodule in the lamina propria of the small intestine; on the right are diffuse and nodular lymphoid tissues in the wall of the appendix. 40x

Epithelium
Lymphoid nodules, more discrete aggregations of lymphoid tissue, are also located in the lamina propria of the GI, respiratory and urogenital systems. As such, they filter tissue fluid and are part of MALT. The illustration on the left shows a nodule in the lamina propria of the small intestine; on the right are diffuse and nodular lymphoid tissues in the wall of the appendix. 40x

Lamina propria
Lymphoid nodules, more discrete aggregations of lymphoid tissue, are also located in the lamina propria of the GI, respiratory and urogenital systems. As such, they filter tissue fluid and are part of MALT. The illustration on the left shows a nodule in the lamina propria of the small intestine; on the right are diffuse and nodular lymphoid tissues in the wall of the appendix. 40x

Muscularis mucosae
Lymphoid nodules, more discrete aggregations of lymphoid tissue, are also located in the lamina propria of the GI, respiratory and urogenital systems. As such, they filter tissue fluid and are part of MALT. The illustration on the left shows a nodule in the lamina propria of the small intestine; on the right are diffuse and nodular lymphoid tissues in the wall of the appendix. 40x

Intestinal glands
Lymphoid nodules, more discrete aggregations of lymphoid tissue, are also located in the lamina propria of the GI, respiratory and urogenital systems. As such, they filter tissue fluid and are part of MALT. The illustration on the left shows a nodule in the lamina propria of the small intestine; on the right are diffuse and nodular lymphoid tissues in the wall of the appendix. 40x

Diffuse lymphoid tissue
Lymphoid nodules, more discrete aggregations of lymphoid tissue, are also located in the lamina propria of the GI, respiratory and urogenital systems. As such, they filter tissue fluid and are part of MALT. The illustration on the left shows a nodule in the lamina propria of the small intestine; on the right are diffuse and nodular lymphoid tissues in the wall of the appendix. 40x

Lymphoid nodules >
Lymphoid nodules are categorized as primary nodules (solid-looking spheres of lymphocytes) or as secondary nodules (consisting of a central, pale zone called the germinal center surrounded by a halo of lymphocytes). Nodules respond to antigens carried in the tissue fluid they filter by increasing activity of phagocytic cells and by forming new lymphocytes in the germinal center.