Why is it possible to deliver more O2 to vigorously working cells without increasing respiration rate or cardiac output?
A. It isn't: a small decrease in PO2 has very little effect on hemoglobin unloading.
B. Because once one molecule of O2 is bound to hemoglobin, the other molecules bind much more rapidly.
C. Because between a PO2 of zero and a PO2 of 40, hemoglobin saturation changes very rapidly and a greater degree of unloading will occur with even small changes in PO2.
D. Because CO2 released from the vigorously working cells enhances O2 binding to hemoglobin.
Answer: C. Because between a PO2 of zero and a PO2 of 40, hemoglobin saturation changes very rapidly and a greater degree of unloading will occur with even small changes in PO2.
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