How are the digestive system and the circulatory system similar?

1. this is not physics this is anatomy.
2.circulatory system is the flow of blood through the vena cava, right artrium, right ventricle, pulmonary valve, pulmonary ventricle, left atrium, left ventricle, arteries, capillaries, veins vena cava. digestive system is food through the esophagus, stomach, etc. no direct relation.

The answer is water molecules are split.cellular respiration and photosynthesis are complement  reactions to each other. these are reverse reactions. in cellular respiration glucose and oxygen yield water and carbon dioxide. so, when respiration begins,  glucose molecules are split. in the opposite reaction - in photosynthesis, carbon dioxide and water yield glucose and oxygen. thus,  when respiration begins, water molecules are split.