The lymphatic system consists of lymphatic vessels and lymph nodes. Blood plasma leaks into the body's tissues through the thin walls of the capillaries. The lymphatic system functions to remove these fluids and materials from tissues, returning them to the bloodstream via lymphatic vessels. The lymphatic system plays a key role in transporting fats from the intestines.

The structure of the lymphatic vessels resembles that of the blood vessels, as the lymphatic vessels also have valves that causes lymph to eventually flow forward instead of travelling backwards. The contraction of your muscles and the pressure in the arteries becomes the pump that helps the fluid move around your body. Exercise can help the lymphatic system to function more effectively.

The lymph passes through lymph nodes before returning to the bloodstream via veins located near the heart. Lymph nodes can be located, for example, in the armpits and the groin. They are rich in white blood cells that help fight microbes that may have entered your lymphatic system. If you have a severe flu, your doctor may test your neck to see if your lymph nodes are swollen.

Left: The lymphatic vessel collects tissue fluid from between cells. Right: The lymphatic system.