How the Diaphragm Powers Breathing: Mechanics of Inspiration & Expiration

The diaphragm, a dome-shaped muscle separating the thoracic and abdominal cavities, is the primary driver of respiration.

Inspiration (Inhalation)

• Diaphragm contracts and flattens, moving downward.
• Thoracic cavity volume increases, lowering intrapulmonary pressure below atmospheric pressure.
• Air flows into the lungs.

Expiration (Exhalation)

• Diaphragm relaxes and returns to dome shape, moving upward.
• Thoracic cavity volume decreases, increasing intrapulmonary pressure.
• Air is expelled from the lungs.

This piston-like action creates the pressure gradients essential for pulmonary ventilation.