Which of the following occurs in the lungs during inspiration?

• A. The thoracic cavity volume decreases.
• B. Air flows out of the lungs.
• C. Alveolar pressure increases above atmospheric pressure.
• D. The diaphragm contracts and moves downward.

Answer: (D)

Verified step by step guidance

1. Understand the process of inspiration: Inspiration is the phase of breathing where air is drawn into the lungs. It involves changes in thoracic cavity volume and pressure to facilitate airflow.
2. Recognize the role of the diaphragm: During inspiration, the diaphragm contracts and moves downward, increasing the vertical dimension of the thoracic cavity.
3. Analyze the effect on thoracic cavity volume: The contraction of the diaphragm, along with the external intercostal muscles lifting the rib cage, increases the thoracic cavity volume.
4. Understand the pressure changes: As the thoracic cavity volume increases, the pressure inside the alveoli (alveolar pressure) decreases below atmospheric pressure, creating a pressure gradient that allows air to flow into the lungs.
5. Eliminate incorrect options: The thoracic cavity volume does not decrease during inspiration, air does not flow out of the lungs, and alveolar pressure does not increase above atmospheric pressure during this phase. The correct answer is that the diaphragm contracts and moves downward.