Which of the following determines the direction of respiratory gas movement in the lungs?

• A. The thickness of the alveolar membrane
• B. The number of red blood cells
• C. Partial pressure gradients of the gases
• D. The temperature of inspired air

Answer: (C)

Verified step by step guidance

1. Understand the concept of respiratory gas exchange: Gas exchange in the lungs occurs due to diffusion, where gases move from areas of higher partial pressure to areas of lower partial pressure.
2. Define partial pressure: Partial pressure refers to the pressure exerted by a single type of gas in a mixture of gases. In the lungs, oxygen and carbon dioxide have specific partial pressures in the alveoli and blood.
3. Identify the role of partial pressure gradients: The direction of respiratory gas movement is determined by the difference in partial pressures (gradient) between the alveoli and the blood. Oxygen moves from the alveoli (higher partial pressure) to the blood (lower partial pressure), while carbon dioxide moves from the blood (higher partial pressure) to the alveoli (lower partial pressure).
4. Eliminate irrelevant factors: The thickness of the alveolar membrane, the number of red blood cells, and the temperature of inspired air do not directly determine the direction of gas movement. These factors may influence the efficiency of gas exchange but not the direction.
5. Conclude that partial pressure gradients are the key determinant: The movement of gases in the lungs is driven by the partial pressure gradients of oxygen and carbon dioxide, ensuring proper gas exchange during respiration.