During respiration, which phase is active?

During respiration, which phase is active?

• A. Inhalation is active
• B. Exhalation is active
• C. Both phases are passive
• D. Neither phase is active

Answer: (A)

Inhalation is active because it requires muscle contraction to expand the chest and lungs. The diaphragm contracts and moves downward, while the external intercostal muscles raise the ribs, increasing thoracic volume and creating a negative pressure that draws air into the airways. Exhalation, at rest, is mainly passive—air leaves the lungs as the lungs and chest wall recoil when the inspiratory muscles relax. Active exhalation can occur during heavy breathing or forced expiration, but under normal conditions the active phase is inhalation.

Inhalation is active because it requires muscle contraction to expand the chest and lungs. The diaphragm contracts and moves downward, while the external intercostal muscles raise the ribs, increasing thoracic volume and creating a negative pressure that draws air into the airways. Exhalation, at rest, is mainly passive—air leaves the lungs as the lungs and chest wall recoil when the inspiratory muscles relax. Active exhalation can occur during heavy breathing or forced expiration, but under normal conditions the active phase is inhalation.