Final answer:
The pressure gradient across the lung wall is the driving force that allows air to flow into and out of the lungs during breathing, with pressures changing during inhalation and exhalation.
Step-by-step explanation:
The pressure gradient across the lung wall is an important factor in pulmonary ventilation. It is the difference in pressure that drives air to flow into and out of the lungs. When you inhale, the pressure inside your lungs drops below atmospheric pressure (negative gauge pressure), and when you exhale, it rises above atmospheric pressure (positive gauge pressure). This pressure difference is what enables the lungs to draw air in and push it out.
Specifically, air flows from the inspired air in the lung (PO₂ = 150 mm Hg) into the bloodstream (PO₂ = 100 mm Hg) due to this pressure difference. The pressure changes with each breath, due to the dynamic nature of the forces within the thorax and the physical structure of the lung wall and its fluid dynamics. The transpulmonary pressure, which is the difference between the intrapleural and intra-alveolar pressures, determines the size of the lungs. The body meticulously maintains the pressures involved to ensure effective breathing.