Which statement best describes the relationship between inhalation and exhalation?

Which statement best describes the relationship between inhalation and exhalation?

• A. Inhalation is active, exhalation is passive due to increased intrathoracic pressure.
• B. Both inhalation and exhalation require muscle contraction.
• C. Inhalation is passive and exhalation is active.
• D. Inhalation occurs due to relaxation of respiratory muscles.

Answer: (A)

Breathing relies on muscle action to create pressure changes inside the chest. Inhalation is an active process: the diaphragm contracts and moves downward while the intercostal muscles lift the ribs, expanding the thoracic cavity. This expansion lowers intrathoracic pressure, pulling air into the lungs. Exhalation at rest is a passive process: when the inspiratory muscles relax, the lungs and chest wall spring back to their normal size (elastic recoil), increasing intrathoracic pressure and pushing air out. The statement that inhalation is active and exhalation is passive due to increased intrathoracic pressure captures these coordinated actions and pressures. During heavy exercise or certain functions (like coughing), exhalation can become active, but at rest it remains passive.

Breathing relies on muscle action to create pressure changes inside the chest. Inhalation is an active process: the diaphragm contracts and moves downward while the intercostal muscles lift the ribs, expanding the thoracic cavity. This expansion lowers intrathoracic pressure, pulling air into the lungs. Exhalation at rest is a passive process: when the inspiratory muscles relax, the lungs and chest wall spring back to their normal size (elastic recoil), increasing intrathoracic pressure and pushing air out. The statement that inhalation is active and exhalation is passive due to increased intrathoracic pressure captures these coordinated actions and pressures. During heavy exercise or certain functions (like coughing), exhalation can become active, but at rest it remains passive.