Final answer:
The residual volume is the amount of air that remains in the lungs after a maximal exhalation and is an important component of lung capacities, ensuring that the lungs do not collapse and that respiratory gases are evenly distributed.
Step-by-step explanation:
The amount of air left in the lungs at the end of a normal breath is referred to as the residual volume (RV). This volume is critical because it prevents the lungs from collapsing and maintains a consistent concentration of respiratory gases in the blood. The residual volume is the amount of air that remains after a maximal, forceful exhalation and cannot be expelled from the lungs. It is one of the four primary lung volumes, along with tidal volume (TV), inspiratory reserve volume (IRV), and expiratory reserve volume (ERV).
Tidal volume measures the amount of air inhaled during a normal breath, while the inspiratory reserve volume is the additional air that can be inhaled after a normal inhalation. The expiratory reserve volume is the additional air that can be exhaled after a normal exhalation. Altogether, these volumes plus the residual volume equal the total lung capacity.