Lymph vessels are similar in structure to the veins but they bear several valves on its surface. These valves impart a beaded appearance to the lymph vessels. They move corresponding to veins and arteries. The valves present on the lymph vessels prevent the back flow of the lymph, once the lymph has entered the main circulatory system. The muscles of the lymph vessel walls contract to help move lymph through the system.
A lymph node is like a filter ball through which lymph passes through before entering the heart. The lymph node walls are perforated tissues which give these nodes a spongy appearance. These filters remove bacteria and help with the immune response; they are essential to the functioning of the immune system. The main group lies in the neck, armpit, chest and abdomen. When a body has an infection in it, these lymph nodes swell to enhance the filtration capacity.