Cardiovascular system a collection of organs whose primary function is to transport blood to and from your body's cells. Digestive system a collection of organs that break down food so that it can be used by the body. Lymphatic system a collection of organs whose primary function is to collect extra-cellular fluid and return it to the blood. Respiratory system a collection of organs whose primary function is to take in oxygen and get rid of carbon dioxide Urinary or Excretory system a collection of organs that remove waste from the blood.