How does blood relate to the respiratory system?
Deoxygenated blood is oxygenated.
In respiratory system, deoxygenated blood is oxygenated. Deoxygenated blood from the heart reaches the lungs via pulmonary artery. This blood is rich in carbondioxide gas. We inhale air which contains 21% of oxygen.
The inhaled air reaches the lungs. The deoxygenated blood also reaches the lungs ( alveoli). There, the exchange of gases takes place because of diffusion (difference in concentration of gases).
We exhale the carbondioxide and the oxygen rich blood goes back to the heart via the pulmonary vein. From heart it is then pumped to various organs.