Question

Choose the correct answer from the alternatives given.
Expiration

• A. occurs when alveolar pressure reaches 758 mm Hg
• B. requires the alveolar pressure to be greater than the atmospheric pressure
• C. involves the expansion of the pleural membranes
• D. occurs when atmospheric pressure is equal to the pressure in the lungs

Answer 1

The correct option is B requires the alveolar pressure to be greater than the atmospheric pressure

During the process of expiration, the diaphragm and intercostal muscles relax. In turn, the thoracic cavity and lungs decrease in volume, causing an increase in interpulmonary pressure and alveolar pressure is positive (i.e higher than the atmospheric pressure). This creates a pressure gradient that causes air to leave the lungs. So, the correct option is 'requires the alveolar pressure to be greater than the atmospheric pressure'.