We have clusters of lymph nodes and they are most notable in your neck and back of head, under groin and under arms. Lymph is the fluid in tissue spaces and carries protein molecules and other substances back to the blood. Lymphatic vessels permit one-way movement of lymph: lymphatic capillaries are tiny, blind ended tubes microscopic in size, one thick cell, porous. Vessels like drainage tiles, low pressure and leaky so liquid can get into them. Lymph is important because it is also a highway in which immune system, cells and chemicals can reach the site of injury or infection. Swelling (edema) of tissues caused by blockage of lymph vessels. Elephantiasis: inflammation of lymph vessels, may progress to septicemia (blood poisoning, sever lymphedema of limbs resulting from parasite infestation of lymph vessels (filariasis, worms in vessels, elephant like appearance in legs. Located in clusters along the pathway of lymphatic vessels. Functions include defense and white blood cell formation.