Final answer:
At functional residual capacity, the pressure in the lungs is zero and equal to the atmospheric pressure, ensuring that the alveoli remain partially inflated for continuous gas exchange.
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. Functional residual capacity (FRC) represents the amount of air that remains in the lung after a normal tidal expiration. This equilibrium in pressure is crucial for preventing lung collapse and facilitating the entry of air into the lungs during the next inhalation cycle.
Intra-alveolar pressure, also known as intrapulmonary pressure, is the pressure within the alveoli, and this pressure equalizes with the atmospheric pressure. At FRC, the lungs contain a mix of air, which includes the amount left from previous respiratory cycles, known as residual volume, ensuring that the alveoli remain partially inflated, even after exhalation, and oxygen exchange can continue.