Lymph nodes become inflamed or enlarged in various diseases, which may range from trivial throat infections to life-threatening cancers.

The condition of lymph nodes is very important in cancer staging, which decides the treatment to be used and determines the prognosis.

Finally, all of these sinuses drain into the efferent lymphatic vessels, which carry the lymph away from the node, exiting at the hilum on the concave side.

These regulate lymphocyte proliferation and migration, antibody secretion, blood perfusion, and inflammatory cytokine production.

The reticular network provides structural support and a surface for adhesion of the dendritic cells, macrophages and lymphocytes.

It also allows 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.

[20] Lymph enters the convex side of a lymph node through multiple afferent lymphatic vessels, which form a network of lymphatic vessels (Latin: plexus) and flows into a space (Latin: sinus) underneath the capsule called the subcapsular sinus.

[4] All of these sinuses drain into the efferent lymphatic vessels to exit the node at the hilum on the concave side.

These vessels are smaller and do not allow the passage of macrophages so that they remain contained to function within a lymph node.

The fewer efferent vessels allow this flow to be slowed, providing time to activate and distribute a larger number of immune cells in the event of an infection.

A lymph node contains lymphoid tissue, i.e., a meshwork or fibers called reticulum with white blood cells enmeshed in it.

[23] The lymph node capsule is composed of dense irregular connective tissue with some plain collagenous fibers, and a number of membranous processes or trabeculae extend from its internal surface.

In some animals they are sufficiently well-marked to divide the peripheral or cortical portion of the node into a number of compartments (nodules), but in humans this arrangement is not obvious.

The larger trabeculae springing from the capsule break up into finer bands, and these interlace to form a mesh-work in the central or medullary portion of the node.

These trabecular spaces formed by the interlacing trabeculae contain the proper lymph node substance or lymphoid tissue.

Some mammal species, such as pigs, rhinoceroses, hippopotamuses, and certain cetaceans, have so-called "inverted" lymph nodes.

In these nodes, the afferent lymph carries antigens from the center (where the B-cell follicles are located) toward the periphery.

Mature B and T lymphocytes exit the lymph node from its periphery directly into the general bloodstream via efferent venules.

The sinus space is criss-crossed by the pseudopods of macrophages, which act to trap foreign particles and filter the lymph.

[29] It may also be generalized, which might suggest infection, connective tissue or autoimmune disease, or a malignancy of blood cells such as a lymphoma or leukemia.

[29] Rarely, depending on location, lymph node enlargement may cause problems such as difficulty breathing, or compression of a blood vessel (for example, superior vena cava obstruction[31]).

[32] Features of the medical history may point to the cause, such as the speed of onset of swelling, pain, and other constitutional symptoms such as fevers or weight loss.

[33] For example, a tumour of the breast may result in swelling of the lymph nodes under the arms[29] and weight loss and night sweats may suggest a malignancy such as lymphoma.

Lymphedema is the condition of swelling (edema) of tissue relating to insufficient clearance by the lymphatic system.

Lymphedema most commonly arises in the arms or legs, but can also occur in the chest wall, genitals, neck, and abdomen.

[37] Secondary lymphedema usually results from the removal of lymph nodes during breast cancer surgery or from other damaging treatments such as radiation.

Although the tonsils and lymph nodes do share certain characteristics, there are also many important differences between them, such as their location, structure and size.