Human: My doctor says I have a swollen lymph node. What is a swollen lymph node? Assistant: 
A swollen lymph node is a swelling of the lymphatic system, which is a network of vessels that helps to fight infection in your body. Lymph nodes are located throughout your body and are made up of tissue that contains lymphocytes, a type of white blood cell. When you get an infection, these cells can increase in number and become swollen.