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How do differences in partial pressure drive the movement of respiratory gases?
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human respiratory system
The lungs serve as the gas-exchanging organ for the process of respiration.
In the human respiratory system, the movement of oxygen and carbon dioxide between the air, blood, and tissues is primarily driven by diffusion. This process relies on the difference in partial pressures of a gas between two locations.1
In a mixture of gases, the partial pressure of each gas is directly proportional to its concentration. A gas will naturally move from an area of higher partial pressure to an area of lower partial pressure, regardless of the distribution of other gases.1
This mechanism facilitates gas exchange across the thin membranous barrier between the alveoli and the pulmonary capillaries:
- Oxygen: Diffuses from the alveoli, where its partial pressure is higher, into the blood, where its partial pressure is lower. It then moves from the blood into body cells down its concentration gradient.12
- Carbon Dioxide: Produced by cellular metabolism, it diffuses from the cells into the blood, and subsequently from the blood into the alveoli to be expelled during exhalation.12