Question

multiple choice question
in external respiration, oxygen diffuses down a partial pressure gradient. the $po_2$ in the alveoli is ___ mm hg, while the $po_2$ in the blood is ___ mm hg.
o 40; 104
o 95; 104
o 104; 95
o 104; 40

Explanation:

External respiration involves oxygen diffusion from alveoli (higher \(PO_2\)) to blood (lower \(PO_2\)). Normal alveolar \(PO_2\) is about 104 mmHg, and normal venous - blood \(PO_2\) (before oxygenation) is about 40 mmHg. After oxygenation, blood \(PO_2\) becomes about 95 mmHg. But in the context of the initial diffusion (alveoli to blood), alveolar \(PO_2 = 104\) mmHg and blood (venous) \(PO_2=40\) mmHg.

Answer:

104; 40