Lymph node

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Lymph nodes are secondary lymphoid organs and play a central role in the body's immune defense. They consist of an outer capsule made of collagenous connective tissue, from which trabeculae or septa extend into the body of the node, which divide the organ into compartments.

Three main areas can be distinguished inside the lymph node: the outer, dark cortex (B zone), the parafollicular zone (T zone) and the inner, lighter medulla. In the cortex there are many lymph follicles with B lymphocytes and the medulla contains medullary cords in which fibroblasts, macrophages and plasma cells can be found. The parafollicular zone is rich in T lymphocytes and contains highly endothelial venules through which lymphocytes can migrate into the lymph node. All cells lie in a tight framework of reticular cells and reticular fibers.

Lymph enters the lymph node via afferent lymphatic vessels through the organ capsule and flows through a lymphatic vessel system called the sinus system. There the lymph is filtered and cleaned of antigens. It leaves the lymph node again at the hilum through efferent lymph vessels. Blood vessels also enter and exit at the hilum.

Watch the following video to learn more about the histology of lymph nodes:

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