Final answer:
At functional residual capacity, the pressure in the lungs is equal to zero, which matches up with the atmospheric pressure, indicating no net airflow.
Step-by-step explanation:
At functional residual capacity (end of quiet expiration) the pressure in the lungs is zero, which is the same as the outside atmospheric pressure. When the muscles relax after inhalation, an elastic recoil of the lungs and chest wall occurs, leading to a gentle exhalation. The intra-alveolar pressure within the alveoli becomes equal to the atmospheric pressure at this point, as there is no net airflow into or out of the lungs. A similar concept is described by Boyle's Law, stating that in a gas, pressure increases as volume decreases, and the target values in breathing are often expressed relative to atmospheric pressure.
The pressure in the lungs at functional residual capacity (end of quiet expiration) is zero, which is the same as the outside atmospheric pressure. During inhalation and exhalation, the pressure in the lungs changes. During inhalation, the pressure in the lungs becomes negative compared to atmospheric pressure, while during exhalation, the pressure becomes positive.