Question

What are the correct partial pressures for oxygen and carbon dioxide, respectively, in alveolar air?

a) 160 mmHg, 0.3 mmHg
b) 100 mmHg, 40 mmHg
c) 40 mmHg, 46 mmHg
d) less than or equal to 40 mmHg, greater than or equal to 46 mmHg

Answer 1

The correct partial pressures in alveolar air are 100 mmHg for oxygen and 40 mmHg for carbon dioxide, facilitated by gradients allowing the diffusion of gases across the respiratory membrane.

Step-by-step explanation:

The correct partial pressures for oxygen and carbon dioxide, respectively, in alveolar air are 100 mmHg for oxygen and 40 mmHg for carbon dioxide. This is because, while the inspired partial pressure of oxygen is approximately 150 mmHg, the mixing with residual air in the lungs that never fully deflates with exhalation reduces this value. Thus, the partial pressure of oxygen in the alveoli is about 104 mmHg but usually given as 100 mmHg for simplicity. Conversely, the partial pressure of carbon dioxide in alveolar air is approximately 40 mmHg, contrasting with the slightly higher 45 mmHg found in the pulmonary capillary blood, creating a gradient that enables the diffusion of carbon dioxide from the blood into the alveoli.