What flows between the respiratory and circulatory system of body?

The respiratory and circulatory systems of the body are connected through the exchange of gases at the level of the肺泡毛细血管床. At this site, oxygen from the alveolar air diffuses into the pulmonary capillaries, while carbon dioxide diffuses from the capillaries into the alveoli. This gas exchange ensures that oxygen-rich blood is pumped from the lungs to the tissues, while carbon dioxide-rich blood returns to the lungs for removal.