Why do the lungs expand as the rib cage lifts and the diaphragm contracts?

• A. The diaphragm contraction increases the pressure inside the lungs, pushing air out.
• B. The rib cage expansion compresses the lungs, forcing air out.
• C. The contraction of the diaphragm directly pulls air into the lungs.
• D. The increase in thoracic volume decreases the pressure inside the lungs, causing air to flow in.

Answer: (D)

Verified step by step guidance

1. Understand the basic mechanics of breathing: Breathing involves changes in pressure and volume within the thoracic cavity, which houses the lungs.
2. Recognize the role of the diaphragm: The diaphragm is a dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. When it contracts, it moves downward, increasing the volume of the thoracic cavity.
3. Consider the rib cage movement: As the diaphragm contracts, the intercostal muscles between the ribs also contract, lifting the rib cage upward and outward, further increasing the thoracic volume.
4. Apply Boyle's Law: According to Boyle's Law, the pressure of a gas is inversely proportional to its volume. As the thoracic volume increases, the pressure inside the lungs decreases.
5. Understand air flow dynamics: With decreased pressure inside the lungs compared to the outside atmosphere, air flows into the lungs to equalize the pressure, facilitating inhalation.