Which statement about the diaphragm is true?

• A. Filters Air
• B. Governs Heart Rate
• C. Pumps Blood Through The Lungs
• D. Primary Muscle Of Breathing

Answer: (D)

The diaphragm is the primary muscle of breathing. When it contracts, it flattens and moves downward, expanding the thoracic cavity and lowering intrapleural pressure. This creates a pressure gradient that pulls air into the lungs, enabling inspiration. It also forms the boundary between the thoracic and abdominal cavities and is innervated mainly by the phrenic nerves.

That makes it the best answer because it directly corresponds to the diaphragm’s central role in ventilation. It does not filter air (that happens in the nasal passages, airways, and lungs), it does not govern heart rate (heart rate is controlled by autonomic input and cardiac conduction), and it does not pump blood through the lungs (the heart’s right ventricle does that; the diaphragm assists breathing, not blood propulsion).