The lymphatic system defends the body from foreign invasion by disease causing agents such as viruses, bacteria, or fungi. The bone marrow, spleen , thymus gland, lymph nodes , tonsils, appendix, and a few other organs. The lymph system contains a network of vessels that assists in circulating body fluids. These vessels transport excess fluids away from interstitial spaces in body tissue and returns it to the bloodstream.
Lymphatic vessels prevent the backflow of the lymph fluid.
They have specialized organs called lymph nodes which filter out destroyed microorganisms. The functioning of the lymphatic system is most easily seen at the microscopic level. Blood cells are produced in the marrow of human bone. When mature, white blood cells actively seek out possible pathogens or unknown substances and, using a complex chemical signaling system, can attack directly or provide for the removal of this substance. If a white blood cell is alerted to the presence of unwanted bacteria in the blood, it will find this bacteria and surround it.