Role of Lymphatic System - Circulation
The lymphatic system plays an important role in body's defence - system by producing lymphocytes and monocytes in the lymph nodes located along major lymph vessels. Lymph nodes are present in birds and mammals only. The phagocytic cells engulf dead cells, cell debris and foreign objects such as bacteria as the lymph filters through the lymph nodes.
In addition to this general phagocytic activity, cells that are present in the lymph nodes as well as in blood, the lymphocytes (white blood cells) are involved in specific defensive responses to infection. Because the lymph nodes are very active in defence responses, they often become swollen and tender during infection. The so called "swollen glands” that often accompany a sore throat are not glands, but active lymph nodes.