The lymphatic system collects fluid that leaks from blood vessels into tissues and returns it to the circulatory system. Lymph vessels contain valves and pass through lymph nodes which filter the fluid and produce lymphocytes to fight infection. The fluid is returned to the circulatory system below the collarbone. Blood transports nutrients, gases, waste, and defenses the body against pathogens. It is composed of plasma and blood cells including red blood cells, white blood cells, and platelets.