National League for Nursing (NLN PAX) Practice Exam

The lymphatic system is primarily responsible for the regulation of fluid balance, absorption of fats from the digestive system, and immune system functions. While it plays a role in transporting lymph, which can contain waste products and other substances, it primarily functions to return excess interstitial fluid to the bloodstream and facilitate the immune response. The other systems listed have direct roles in excretion. The digestive system eliminates solid waste through feces, the respiratory system expels carbon dioxide and some water vapor as waste, and the excretory system (or urinary system) is responsible for filtering blood, removing waste, and regulating fluid balance through urine. Therefore, since the lymphatic system does not have a primary function in the direct excretion of waste products from the body, it is the correct choice for the organ system that does not contribute to the excretion of substances.