Question

During expiration the pressure within the lungs is ________with respect to the atmosphere.

• A. negative
• B. positive
• C. both positive and negative
• D. none of the above

Answer 1

The correct option is B positive

During expiration the rib cage moves inwards. The diaphragm relaxes and returns to its dome shape. As a result of the movement of the rib cage and diaphragm, the volume within the lungs decreases. As the volume decreases the pressure within the lungs increases and goes higher than the atmospheric pressure. Thus, the pressure within the lungs is said to be positive with respect to the atmosphere. This is the reason the air is pushed out to the atmosphere.