Which best describes the concept of partial pressure in the context of gas exchange?

• A. Pressure exerted by a mixture of gases
• B. Pressure exerted by a specific gas in a mixture
• C. Pressure required for lung inflation
• D. Total pressure in the alveolar space

Answer: (B)

Partial pressure refers specifically to the pressure exerted by an individual gas in a mixture of gases. In the context of gas exchange, it is crucial for understanding how gases like oxygen and carbon dioxide move between the alveoli in the lungs and the blood. Each gas contributes to the total pressure of the atmosphere, and the partial pressure indicates how much of that total pressure is attributable to one specific gas.

For example, in the lungs, the partial pressure of oxygen influences diffusion into the blood, while the partial pressure of carbon dioxide affects its diffusion out of the blood. This concept is central to gas exchange because it determines the direction and rate at which gases diffuse according to their concentration gradients. Understanding partial pressure is vital for grasping how respiration and cellular metabolism are interlinked, illustrating how gas transport is dependent on these pressure gradients rather than the total atmospheric pressure or specific requirements for lung inflation.