During quiet breathing inspiration, what happens to thoracic volume?

• A. Increases
• B. Decreases
• C. Remains the same
• D. Fluctuates

Answer: (A)

During quiet breathing, inspiration involves the contraction of the diaphragm and intercostal muscles, leading to an increase in thoracic volume. As the diaphragm contracts, it moves downward, while the intercostal muscles pull the rib cage outward and upward. This expansion of the thoracic cavity creates a negative pressure relative to the atmospheric pressure, allowing air to flow into the lungs.

The increase in thoracic volume is essential for facilitating gas exchange, as it allows the lungs to expand and fill with air. This process is vital for bringing oxygen into the body and expelling carbon dioxide, aligning with the fundamental principles of ventilation. The other options are not consistent with the physiological changes occurring during quiet inspiration; for instance, a decrease in thoracic volume would imply that the lungs are collapsing rather than expanding, which is not the case in normal breathing conditions.