Question

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at the arterial ends of the pulmonary capillaries...
multiple choice
the $po_2$ is lower in the capillaries than in the alveoli
the $po_2$ is higher at first in the capillaries than in the alveoli, and then it is lower in the alveoli than in the capillaries
the $po_2$ is higher in the capillaries than in the alveoli
the $po_2$ is equal in the capillaries and in the alveoli

Explanation:

Gas exchange in the lungs occurs based on the principle of diffusion. Oxygen diffuses from an area of higher partial pressure to an area of lower partial pressure. In the pulmonary capillaries at the arterial end, the blood is de - oxygenated (has a lower \(PO_2\)). The alveoli have a higher \(PO_2\) because they are continuously supplied with fresh air. So, oxygen will diffuse from the alveoli (higher \(PO_2\)) to the capillaries (lower \(PO_2\)).

Answer:

The \(PO_2\) is lower in the capillaries than in the alveoli.