For inspiration of air. which of the following happens first?

For inspiration of air, which of the following happens first A. Intrapulmonary pressure drops B. Diaphragm descends, thoraic volume begins to increase, and rib cage rises. C. air (gases) flows into the lungs. D. Thoracic cavity volume decreases.


Correct answer: Option B Explanation:
  • The diaphragm is the principal muscle of inspiration.
  • Diaphragm contraction causes the diaphragm to descend.
  • This increases the thoracic volume.
  • The intrapleural pressure becomes more negative.
  • This leads to increase in the volume of the alveoli.
  • Increase in the volume of the alveoli leads to reduction in the pressure inside the alveoli ( This pressure is also called intrapulmonary pressure)
  • The pressure in the alveoli becomes negative in relation to the atmosphere.
  • This leads to movement of air into the lungs.
Incorrect answer: Option A: During inspiration the Intrapulmonary pressure does drop but this is not the first thing that happens. Option C: During inspiration, gas does flow into the lungs but this it that last things that happens

Option D: The thoracic volume increases during inspiration. The thoracic volume decrease during expiration.

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