What drives the air out of the lungs during quiet expiration?

• A. Contraction of the diaphragm
• B. Contraction of the external intercostal muscles
• C. Active contraction of the abdominal muscles
• D. Elastic recoil of the lungs and chest wall

Answer: (D)

Verified step by step guidance

1. Understand the process of quiet expiration: Quiet expiration is a passive process, meaning it does not require active muscle contraction.
2. Identify the role of the diaphragm and intercostal muscles: During quiet expiration, the diaphragm and external intercostal muscles relax, rather than contract.
3. Recognize the concept of elastic recoil: Elastic recoil refers to the natural tendency of the lungs and chest wall to return to their original shape after being stretched or expanded during inhalation.
4. Explain how elastic recoil drives air out: As the lungs and chest wall recoil, the volume of the thoracic cavity decreases, increasing the pressure inside the lungs and pushing air out.
5. Differentiate between active and passive expiration: Active expiration involves muscle contraction, such as the abdominal muscles, while quiet expiration relies on the passive elastic recoil of the lungs and chest wall.