Final answer:
The alveolar pressure and intrapleural pressure change during different phases of breathing. During inspiration and expiration, the alveolar pressure deviates from atmospheric pressure. However, the intrapleural pressure remains constant at approximately -4 mm Hg.
Step-by-step explanation:
The alveolar and intrapleural pressures play a crucial role in the process of breathing. At rest, the alveolar pressure is equal to atmospheric pressure (760 mm Hg), while the intrapleural pressure is around -4 mm Hg. During inspiration, the alveolar pressure decreases, creating a pressure gradient that allows air to flow into the lungs. At this point, the intrapleural pressure becomes more negative, reaching around -6 mm Hg. During inspiratory capacity (IC), which is the maximum amount of air inhaled after a normal expiration, the alveolar pressure is slightly below atmospheric pressure (758 mm Hg), while the intrapleural pressure remains at around -4 mm Hg. During expiration, the alveolar pressure increases above atmospheric pressure (762 mm Hg), causing air to flow out of the lungs. At the same time, the intrapleural pressure stays around -4 mm Hg.