Question

Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because

• A. There is a positive intrapleural pressure.
• B. Pressure in the lungs is higher than the atmospheric pressure.
• C. There is a negative pressure in the atmosphere.
• D. There is a negative intrapleural pressure pulling the walls of the lungs.

Answer 1

The correct option is D There is a negative intrapleural pressure pulling the walls of the lungs.

Lungs do not collapse between breaths as some air always remain in the lung which can never be expelled because the negative intrapleural pressure is created by two opposing elastic forces pulling in the intrapleural space. The elastic lungs tend to collapse while the elastic chest wall tends to thrust outward. These two opposite forces create a negative intrapleural pressure which in turn opposes the natural tendency of lungs to collapse.

Therefore, the correct answer is option D.