Lymph nodes also have clinical significance. They become inflamed or enlarged in various conditions, which may range from the trivial, such as a throat infection, to life-threatening conditions such as cancers. In the latter, the condition of lymph nodes is so significant that it is used for cancer staging, which decides the treatment modalities to be employed, and for determining the prognosis.

Lymph nodes can also be used for diagnosis by biopsy whenever they are inflamed. Certain diseases affect lymph nodes with characteristic consistency and location.

Function

Pathogens can set up infections anywhere in the body. However, lymphocytes will meet the antigens in the peripheral lymphoid organs, which includes lymph nodes. The antigens are displayed by specialized cells in the lymph nodes. Naive lymphocytes, naive meaning the cells have not encountered an antigen yet, enter the node from the bloodstream through specialized capillary venules. After the lymphocytes specialize they will exit the lymph node through the efferent lymphatic vessel with the rest of the lymph. The lymphocytes continuously recirculate the peripheral lymphoid organs and the state of the lymph nodes depends on infection. During an infection the lymph nodes can expand due to intense B-cell proliferation in the germinal centers, this is commonly referred to as swollen glands.

Structure

Thin reticular fibers, elastin and reticular fibers form a supporting meshwork called reticular network (RN) inside the node, within which the white blood cells (WBCs), most prominently, lymphocytes are tightly packed as follicles in the cortex. Elsewhere, there are only occasional WBCs. The RN provides not just the structural support, but also provide surface for adhesion of the dendritic cells, macrophages and lymphocytes. It allows for exchange of material with blood through the high endothelial venules and provides the growth and regulatory factors necessary for activation and maturation of immune cells.

The number and composition of follicles can change especially when challenged by an antigen, when they develop a germinal center.

A lymph sinus is a channel within the lymph node lined by the endothelial cells along with fibroblastic reticular cells and allows for smooth flow of lymph through them. Thus, subcapsular sinus is a sinus immediately deep to the capsule, and its endothelium is continuous with that of the afferent lymph vessel. It is also continuous with similar sinuses flanking the trabeculae and within the cortex (cortical sinuses). The cortical sinuses and that flanking the trabeculae drain into the medullary sinuses, from where the lymph flows into the efferent lymph vessel.