During ventilation, how do membranes affect surface area and membrane thickness?

• A. Stretch, increases, decreases
• B. Compress, decreases, increases
• C. Lengthen, increases, decreases
• D. Shrink, decreases, increases

Answer: (A)

During ventilation, the optimal functioning of gas exchange relies heavily on the properties of the membranes involved. The correct choice illustrates that when membranes stretch, they increase the surface area available for gas exchange while simultaneously reducing the thickness of the membrane.

A larger surface area allows for more sites where oxygen and carbon dioxide can diffuse, thereby enhancing the efficiency of gas exchange. Additionally, a thinner membrane permits gases to diffuse more easily; the greater the thickness, the longer the distance gas molecules must travel, which can slow down the rate of diffusion. Therefore, during active ventilation, when the lungs inflate and stretch, both the increase in surface area and the decrease in membrane thickness facilitate a more efficient exchange of gases between the alveoli and blood.

This principle underscores the importance of membrane dynamics in respiratory physiology, as it directly relates to how well the body can oxygenate blood and remove carbon dioxide.