Fig. 2.
The oxygen pathway of respiration. Drawing of an alveolus adjoining a pulmonary capillary, where oxygen (O2) and carbon dioxide (CO2) are exchanged; blood flow exiting the alveolus enters the arterial circulation (right), crosses through the interstitium and tissues, and returns to the pulmonary capillary through the venous system (left). Partial pressure values are in mmHg. Pio2, Po2 in the inspired air; Pvco2, mixed venous carbon dioxide tension; Pvo2, mixed venous oxygen tension.