Final answer:
The oxygen partial pressure of the alveoli is lower than atmospheric oxygen partial pressure because oxygen is removed by the blood, the alveoli air is more humidified, and it has a higher carbon dioxide content. The correct option isa. lower than
Step-by-step explanation:
In a tidal gas exchange system, the oxygen partial pressure of the alveoli is lower than that of atmospheric oxygen partial pressure. This is due to the fact that oxygen is continuously removed from the alveolar air by the blood. Additionally, the alveolar air is humidified as the respiratory system works to add moisture to incoming air.
This increases the water vapor in the alveolar air, further diluting the oxygen concentration and thereby decreasing its partial pressure. The alveoli also contain a higher amount of carbon dioxide, due to gas exchange adding carbon dioxide from the blood into the alveolar air, which also contributes to the lower partial pressure of oxygen.
When comparing the partial pressure of oxygen in venous blood in an alveolus to air, and between arterial blood and body tissues, it's noteworthy that the partial pressure of oxygen in the venous blood is lower than that in the alveolar air, which is why oxygen diffuses into the blood.
The arterial blood, which has collected oxygen from the lungs, has a higher partial pressure of oxygen than the tissues, allowing oxygen to diffuse from the blood into body tissues where it is needed for cellular respiration.
The correct option isa. lower than