Blood gases alveolus-pulmonary capillary

Fig. 1 Schematic representation of the blood-gas barrier at the level of the alveolus-pulmonary capillary...

For gas exchange to occur properly in the lung, air must be dehvered to the alveoK via the conducting airways, gas must diffuse from the alveoli to the capillaries through extremely thin walls, and the same gas must be removed to the cardiac atrium by blood flow. This three-step process involves (1) alveolar ventilation, (2) the process of diffusion, and (3) ventilatory perfusion, which involves pulmonary blood flow. Obviously, an alveolus that is ventilated but not perfused cannot exchange gas. Similarly, a perfused alveolus that is not properly ventilated cannot exchange gas. The most efficient gas exchange occurs when ventilation and perfusion are matched. 

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