The Circulatory System is about the Blood and the heart: they deliver oxygen to the rest of the body (except lungs). AFTER they deliver the oxygen they get the waste (Carbon Dioxide) and deliver it to the LUNGs (Respiratory System)
The Respiratory system is about the Lungs, Bronchi, Alveoli, Trachea, etc. They EXCHANGE the carbon dioxide from the blood with oxygen, they do this in the ALVEOLI (a small, grape-like sockets in the lungs).
The Digestive System consist the Esophagus, Stomach, Intestines, Gallbladder, and Anus. They Digest the food, they ABSORB the nutrients from the food we eat and we poop out the UNNECESSARY wastes.
