What volume remains in the lungs after a tidal volume is expired?

The volume that remains in the lungs after a tidal volume is expired is referred to as functional residual capacity (FRC). FRC represents the amount of air that is left in the lungs after a person has completed a normal, quiet expiration. This volume includes both the residual volume, which is the air that cannot be forcibly exhaled, and the expiratory reserve volume, which is the additional air that can be expired after a normal expiration.

Understanding FRC is essential because it plays a critical role in maintaining gas exchange and ensuring that the lungs do not completely empty with each breath. This residual air helps to stabilize alveolar gas concentrations, preventing large fluctuations in oxygen and carbon dioxide levels between breaths.

The other options refer to different lung volumes: residual volume specifically pertains to the volume of air remaining in the lungs after maximum exhalation, tidal volume is the amount of air inhaled or exhaled during normal breathing, and total lung capacity is the total volume of air the lungs can hold, which includes all the lung volumes. Thus, the best choice depicting the volume remaining after a tidal volume is expired is functional residual capacity.