Growing And body System

Why is circulatory , respiratory , digestive and excretory system are considered transport systems for the body ? They are are included as the body system because with out the parts of the body system we won't be able to live . Circulatory means relating to the circulation of blood or sap . Respiratory of , relating to or affecting respiration or the organs of respiration ; respiratory disease . Digestive of or relating to the process of digesting food : stomach ulcers and other digestive disorders . Excretory of relating to, or concerned with excretion the excretory organs . That why they are part of the body system.