At a high camp, a climber's alveolar pO₂ falls from 104 mm Hg to 80 mm Hg…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
At a high camp, a climber's alveolar pO falls from mm Hg to mm Hg. Use the readings of the problem on reading the curve: the saturation is per cent at mm Hg and per cent at mm Hg.
- By how many per cent points does the saturation of the blood leaving the lungs fall?
- Why is the fall so small?
- Which part of the curve explains it?
Need a reminder? The key ideaShow
The oxygen dissociation curve is S-shaped. At mm Hg haemoglobin is about per cent saturated, and at mm Hg about per cent. A higher pCO, more hydrogen ions or a higher temperature shift it to the right, and oxygen is released more easily.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Saturations: at mm Hg and at mm Hg.
Plan. Subtract, then relate the answer to the shape of the curve.
Step 1. (a) points.
Step 2. (b) The pO fell by mm Hg, but the saturation fell by only points.
Step 3. (c) The flat upper part of the S-shaped curve explains it. There, a large change in pO makes only a small change in saturation.
Answer: points. The flat top of the curve protects the saturation of the blood.
Check. At the steep part, below mm Hg, a fall of mm Hg would cost far more.
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