Organized Lymphoid Tissue - pediagenosis
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Wednesday, September 23, 2020

Organized Lymphoid Tissue

Organized Lymphoid Tissue

The role of the bone marrow in hematopoiesis and of the thymus in T‐cell development will be discussed in Chapter 10. As already discussed, the MALT deals with antigens present at mucosal surfaces. In contrast, the lymph nodes receive antigen either draining directly from the tissues or carried by dendritic cells, and the spleen monitors the blood. 

The distribution of major lymphoid tissues throughout the body

Figure 6.11 The distribution of major lymphoid tissues throughout the body.

The anatomical location of these lymphoid tissues is illustrated in Figure 6.11. Immunological communication between these tissues and the rest of the body is maintained by a pool of recirculating lymphocytes that, as already discussed, passes from the blood into the lymph nodes, spleen and other tissues and back to the blood by the major lymphatic channels such as the thoracic duct (Figure 6.12).

Figure 6.12 Traffic and recirculation of lymphocytes through encapsulated lymphoid tissue and sites of inflammation. Bloodborne lymphocytes enter inflamed tissues when they recognize upregulated adhesion molecules on the blood vessel endothelium and enter lymph nodes by passing through the highwalled endothelium of the postcapillary venules (HEV). They leave via the draining lymphatics. The efferent lymphatics join to form the thoracic duct, which returns the lymphocytes to the bloodstream. In the spleen, which lacks HEVs, lymphocytes enter the lymphoid area (white pulp) from the arterioles, pass to the sinusoids of the erythroid area (red pulp) and leave by the splenic vein (see Figure 6.16b). Traffic through the mucosal immune system was illustrated in Figure 6.7.

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