Final answer:
The chest wall expands outward when the diaphragm contracts during inhalation, causing air to flow into the lungs due to lower pressure inside. During exhalation, the diaphragm relaxes, the chest contracts, and air is passively expelled due to the increased pressure.
Step-by-step explanation:
The chest wall is anatomically configured to expand outward. The lungs adhere to the chest wall as it expands outward. As the diaphragm contracts, it flattens and increases the volume inside the pleural cavities, which decreases the pressure within them. Consequently, air flows into the lungs. When the diaphragm relaxes, the chest contracts, and air flows out. The action of breathing primarily depends on the contractions of the diaphragm, thoracic wall compliance, and the structure of the lungs. During inhalation, the diaphragm contracts, lowering itself and the intercostal muscles contract to expand the chest wall outward. This causes the intrapleural pressure to drop and the lungs to expand, drawing air into the airways. Upon exhalation, the intercostal muscles and diaphragm relax, the chest wall returns back to its resting position, and the increase in thoracic cavity pressure forces air out of the lungs in a passive process.