Light micrograph of transverse section through a vessel in the human lymphatic system, showing a one-way valve. The lymphatic system is a network of lymph vessels running beneath the skin which serve lymph nodes in the neck, armpits, groin and abdomen. It drains fluid (lymph) from body tissues through body movement and one-way valves. This system contains white blood cells which destroy disease vectors, giving it a vital role in the body's immune system response.