Exhalation is which part of ventilation?

• A. The passive part of ventilation
• B. The active part of ventilation
• C. External respiration
• D. Cellular respiration

Answer: (A)

Ventilation has two phases, inhalation and exhalation, and exhalation is the passive part during normal, resting breathing. When the inspiratory muscles relax, the lungs and chest wall recoil to their resting positions, reducing the thoracic volume and pushing air out without active muscular effort. Inhalation, by contrast, is the active phase because it requires diaphragm and intercostal muscle contraction to enlarge the chest cavity and draw air in. Exhalation can become active only during heavy or forced breathing, but under typical conditions it remains passive. External respiration and cellular respiration are different processes: external respiration is the gas exchange between air and blood in the alveoli, while cellular respiration is the cell’s use of oxygen to produce energy.