Vessels and lymph nodes return fluid and protein to the blood. The function of the lymphatic system is to help defend the body against infection and maintain the volume and protein concentration of the blood. Lymph is the fluid within the lymphatic system comprised of white blood cells and waste products from tissues. Lymph vessels are like veins. They prevent the backflow of fluid toward the capillaries.
Capillaries are microscopic vessels.
Lymph nodes are organs located along the lymph vessels that filter the lymph of harmful bacteria or viruses. There are a few stages of lymphedema which categorize the severity. If no swelling is apparent and the arm seems almost identical to the opposite arm, lymphedema is not present. This stage is called the latency stage, which precedes lymphedema. Stage one is the mild stage.