The respiratory system is responsible for the processes that bring oxygen into our body and remove carbon dioxide generated during cellular respiration. This exchange between oxygen and carbon dioxide takes place from our blood at the lungs. The digestive system is responsible for the breakdown of the food that we eat into smaller molecules that can be absorbed by our blood. For example, carbohydrates are broken down into glucose, proteins into amino acids and lipids into fatty acids. All these processes require energy, which is generated by (aerobic) respiration of glucose in our body. This process requires oxygen, which is supplied by respiratory system and generates carbon dioxide, which is removed by the respiratory system. The digestive system also requires the contraction of muscles to break down food and push it through the digestive tract, which is helped by respiratory system (which in turn needs movement of these muscles for air passage into our body). The digestive system and respiratory system also share an organ -the pharynx.
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