Question

During external respiration the PCO₂ in the alveolar decreases from ___ mmHg to ___ mmHg.

Answer 1

During external respiration, the partial pressure of carbon dioxide (PCO₂) in the alveolar air decreases from 45 mmHg to 40 mmHg as CO₂ diffuses from the blood into the alveoli.

Step-by-step explanation:

The PCO₃ in the alveolar drops from about 45 mmHg to 40 mmHg during external respiration. Following its concentration gradient, carbon dioxide diffuses into the alveoli from the capillaries. Approximately 45 mmHg of carbon dioxide are found in the capillaries, whereas 40 mmHg is found in the alveoli. The transfer of gases required for breathing is made possible by the diffusion of CO2 into the alveoli from the capillaries.