What are lymph nodes? Lymph nodes are small, grape-sized glands that exist throughout the body and make up part of the lymphatic fluid circulation system. Lymphatic fluid (or lymph) is a clear fluid that leaks out of blood vessels, and in order for the body to keep the blood volume constant, is collected and returned to the blood via the lymphatic circulation. Lymph nodes are connected to each other by lymph vessels that transfer the lymphatic fluid. Before returning the lymph to the blood, lymph nodes clean up the fluid, filtering out infection-causing germs (bacteria, viruses, etc.) and helping to fight any infections that may be present. Most people can remember having swollen "glands" under their neck when they had an infection. Those "glands" were swollen lymph nodes that were reacting to the infection. Clusters of lymph nodes exist in particular parts of the ... read more on Pediatric Hodgkin's Disease: The Basics