Which term refers to the volume of air present in the lungs at the end of passive expiration?

The term that refers to the volume of air present in the lungs at the end of passive expiration is functional residual capacity. This volume represents the total amount of air remaining in the lungs after a normal, passive exhalation, encompassing both the residual volume and the expiratory reserve volume.

Functional residual capacity is essential for maintaining adequate gas exchange during the breathing cycle, as it prevents the complete collapse of the alveoli and allows for a continuous supply of oxygen to the bloodstream. It reflects how much air remains in the lungs during normal resting breathing and is particularly important in assessing lung function and diagnosing various respiratory conditions.

Understanding this concept helps in evaluating aspects of pulmonary health and function, as abnormalities in functional residual capacity can indicate problems such as restrictive or obstructive lung diseases.