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

Answer 1

The correct option is D There is a negative intrapleural pressure pulling at the lung walls

The movement of air inside and outside the lungs is due to the pressure gradient created. There always exists a negative intrapleural pressure, which prevents the lungs from collapsing.
Intrapleural pressure is the pressure within the pleural cavity, which is normally less than atmospheric pressure. There exists a trans pulmonary pressure, that is difference between intrapulmonary pressure and intrapleural pressure, which keeps the lungs inflated.