What does it mean if oxygen is operating on the steep part of the oxygen-dissociation curve?
In: Biology
If you plot a graph with the Y axis being the proportion of hemoglobin that is saturated with oxygen and on the X axis the oxygen tension (basically partial pressure of oxygen or amount of it in the blood), you get a sigmoidal curve. This means the curve is not linear, and there are all sorts of reasons for this that I won’t get into. But what this means is that for a given change in oxygen tension, you get different changes in hemoglobin saturation depending on the range of the absolute amount of oxygen. For example if you increase oxygen tension from 2 to 3 (random units) you may get an increase of hemoglobin saturation from 5 to 7. But if you increase oxygen tension from say 8 to 9 (still just one unit difference), you get a change in saturation from say 10 to 20. But if you keep increasing, eventually the change slows down again. That’s the sigmoidal curve.
Hemoglobin in capillaries operates in the steepest part of the curve means that in the capillaries the range of oxygen tensions that can exist occurs in the part of the curve where hemoglobin saturation changes the most for a given change in oxygen tension. Why is this good? Because that means even a tiny drop in oxygen tension in a given tissue would result in a large scale unloading of oxygen from the hemoglobin. This is important because the system becomes sensitive to even small changes. Some tissues may be highly metabolically active, others not so much, and hemoglobin releases the corresponding amount of needed oxygen regardless of how small the actual change in oxygen tension is.
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