Picture shows the regions of the lymph node where the blood stream (arteries and veins) enter a typical lymph node. For the lymphatic system to function properly in its defensive role, the lymph nodes must be able to "dump" their leukocytes (infection fighting cells) quickly into the general blood stream. It is important to note that white blood cells are not produced in the Lymph nodes initially, only stored there. In the event of a serious infection (a pathogenic virus for example), the lymph nodes often become very swollen. This swelling represents the explosive multiplication of leukocyte numbers in the lymph node's honeycomb of connective tissue.