Functional residual capacity represents the volume of air remaining in lungs:-

Functional residual capacity: - It equals the EXPIRATORY RESERVE VOLUME + RESIDUAL VOLUME - This capacity is amount of air that remains in lungs at end of normal expiration (about 2300 ML) Pulmonary capacities: Inspiratory capacity: - Tidal volume + inspiratory reserve volume - This capacity is amount of air a person can breathe in, beginning at normal expiratory level & distending the lungs to maximum amount. Vital capacity: - Inspiratory reserve volume + tidal volume + expiratory reserve volume. - This capacity is max amount of air a person can expel from lungs after first filling the lungs to their maximum extent & then expiring to maximum extent (about 4600ml) Total lung capacity: - Max vol to which lungs can be expanded with greatest possible effo - Vital capacity + residual volume