The lymph system is a network of vessels and organs throughout the body. This network carries a fluid that contains special white blood cells called lymphocytes between the body tissues and the blood.

The lymph system includes the lymph nodes, tonsils, thymus, spleen, and bone marrow. The lymph nodes filter lymph fluid as it flows through them, trapping bacteria, viruses, and other foreign substances, which are then destroyed by the lymphocytes.

The lymph system is also an important part of the immune system, the body's defense against disease. When a part of the body is infected, the nearby lymph nodes become swollen as they collect and destroy the infecting organisms. For example, if a person has a throat infection, lymph nodes in the neck may swell and become tender.

Sometimes diseases, like cancer, can begin and spread through the lymph system.