What is the amount of air that normally reaches the alveoli in an adult?

The amount of air that normally reaches the alveoli in an adult, referred to as the alveolar ventilation, is approximately 350 mL. This figure represents the volume of fresh air that is available for gas exchange in the alveoli during each respiratory cycle.

When a person inhales, not all the air that enters the respiratory system reaches the alveoli due to anatomical dead space, which includes the parts of the respiratory system where gas exchange does not occur, such as the trachea and bronchi. Typically, the volume of this dead space in an adult is around 150 mL, which means that out of the standard tidal volume (total air breathed in and out per breath, which is about 500 mL on average), approximately 350 mL actually contributes to effective gas exchange in the alveoli.

This calculation is crucial for understanding how effectively a person's respiratory system is functioning and is fundamental to the assessment and management of various respiratory conditions. It highlights the importance of considering both the tidal volume and the dead space when evaluating respiratory dynamics.