Q.State the volume of air remaining in the lungs after a normal breathing.
After an ordinary breath out, the lungs are not empty — the air still inside them is called the functional residual capacity.
During quiet, everyday breathing you never squeeze all the air out of your lungs. Each normal breath out pushes out only the tidal volume, and a considerable amount of air remains behind in the airways and alveoli. This leftover air, measured at the end of a normal expiration, is called the functional residual capacity.
It is helpful to see what this capacity is built from, because it is a combination of two separate volumes:
- the expiratory reserve volume — the extra air that a person could still force out if they made a deliberate, maximal effort after the normal breath, and
- the residual volume — the air that stays in the lungs even after the most forcible expiration and simply cannot be breathed out.
Adding these two together gives the functional residual capacity: the total air present in the lungs once a relaxed, normal breath out is finished.
This is different from the residual volume alone. Residual volume is what is left after the strongest possible expiration; functional residual capacity is what is left after an ordinary, effortless one, so it includes both the residual volume and the still-expellable expiratory reserve.
In short, the air remaining in the lungs after a normal expiration is the functional residual capacity — the expiratory reserve volume plus the residual volume.
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