Which statement best describes the factors governing gas absorption in the lungs?

Which statement best describes the factors governing gas absorption in the lungs?

• A. Absorption is determined only by diffusion distance.
• B. Partial pressure difference drives absorption, and solubility in blood plays a role.
• C. Gas diffusion is not affected by pressure.
• D. Absorption is independent of diffusion and perfusion.

Answer: (B)

Gas transfer in the lung is driven by the difference in partial pressures of a gas between the alveolar air and the blood, and how soluble that gas is in blood. The driving force is the partial pressure gradient: oxygen moves from the alveoli, where its partial pressure is high, into the blood where it’s lower, while carbon dioxide moves from the blood, where its partial pressure is higher, into the alveoli to be exhaled. How much of the gas actually dissolves in the blood—and thus becomes available for transport—depends on its solubility in blood, described by Henry’s law. A gas that is more soluble will dissolve more readily and diffuse more quickly for a given gradient. Other factors like membrane thickness, surface area, and blood flow modulate the rate, but the essential determinants are the partial pressure difference and the gas’s solubility. That’s why the statement linking a driving pressure difference with the role of solubility best describes gas absorption in the lungs.

Gas transfer in the lung is driven by the difference in partial pressures of a gas between the alveolar air and the blood, and how soluble that gas is in blood. The driving force is the partial pressure gradient: oxygen moves from the alveoli, where its partial pressure is high, into the blood where it’s lower, while carbon dioxide moves from the blood, where its partial pressure is higher, into the alveoli to be exhaled. How much of the gas actually dissolves in the blood—and thus becomes available for transport—depends on its solubility in blood, described by Henry’s law. A gas that is more soluble will dissolve more readily and diffuse more quickly for a given gradient. Other factors like membrane thickness, surface area, and blood flow modulate the rate, but the essential determinants are the partial pressure difference and the gas’s solubility. That’s why the statement linking a driving pressure difference with the role of solubility best describes gas absorption in the lungs.