Lymph nodes are structures in the lymphatic system. Your lymphatic system is an extensive network of lymphatic vessels distributed all over the body. Everyday we are exposed to pathogens that have the potential of causing us great harm. The lymphatic system is part of our defense mechanisms or immunologic response that fights off these pathogens and keeps us relatively healthy. The system as a whole is comprised of lymphatic vessels, lymph nodes, lymphatic tissue like the tonsils, thymus, and spleen. Basically, the system is a biological filter, the lymph nodes filter the lymph as it passes through, the lymphatic fluid is then returned to the venous circulation via the thoracic duct and right lymphatic duct. The lymph nodes are important because they are located in clusters along the route that the lymphatic fluid passes and remove these harmful substances from the lymph.
The lymph nodes are very important for the proper functioning of the immune system in addition to filtering/trapping foreign objects that shouldn't be there. Lymph nodes filter pathogens from the blood from anywhere in the body (this is why lymph nodes are everywhere) by way of the white blood cells lymphocytes. Lymph nodes can become swollen due to infections. Clinically the condition of the lymph nodes is extremely important in cancer patients as they are used to determine the stage the cancer is at, what treatments to use, and the person's prognosis. The health of a person's lymph nodes can say a great deal about the condition of a person's immune system, as well as aide in planning treatments, and determining how severely infected a person is.
Another name for lymph nodes are glands and they are like filters. They are important because they help the body to fight off infection. Sometimes when the lymph nodes become swollen it is because they are currently fighting off something that is try to infect the body. This is why they are so important to the the body. Without them, we would be more likely to be ill. Sometimes people have some of their lymph nodes removed. For example, perhaps they have had cancer or the nodes themselves have become infected. However, there are lymph nodes located all over the body to compensate for the ones that have been removed.