alleryStart learning →What drives air out of the lungs during normal quiet expiration?
AContraction of the internal intercostal muscles
BElastic recoil as the breathing muscles relax
CContraction of the abdominal oblique muscles
DActive shortening of the alveolar walls
Answer & Solution
Correct answer: B. Elastic recoil as the breathing muscles relax
1. Normal expiration is passive, so no energy is required to push air out.
2. The diaphragm and intercostal muscles relax and the elasticity of lung tissue causes the lung to recoil.
3. Thoracic and lung volume fall, intrapulmonary pressure rises above atmospheric, and air leaves.
4. The internal intercostals and abdominal muscles are recruited only for forced expiration, which is why the first and third options are wrong here.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 22 "The Respiratory System", section 22.3 The Process of Breathing_
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