Final answer:
The partial pressure of oxygen and carbon dioxide is the result of the continuous exchange of gases between the blood and alveolar air in the lungs.
Step-by-step explanation:
The continuous exchange of gases between the blood and alveolar air in the lungs results in a partial pressure of oxygen and carbon dioxide.
During external respiration, oxygen diffuses from the alveoli into the blood across the pulmonary capillaries, where the partial pressure of oxygen is higher in the alveoli than in the blood. Conversely, carbon dioxide, which is more concentrated in the blood, diffuses from the blood into the alveoli.