Nyphool

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For those who use kaplan. There seems to be a contradiction. In the review notes in the respiration system chapter. It says that at high altitudes, the affinity of hemoglobin for oxygen decreases to facilitate unloading of oxygen in tissues. Then i would assume that at high altitudes, the oxygen dissociation curve would shift to the right since fetal hemoglobin would shift the curve to the left cuz it has a higher affinity for oxygen. However, in kaplan full length 4-passage 7. It says that high altitudes lead to the exhalation of co2 and an increase in blood pH. an increase in blood ph would shift the curve to the left because acording to Bohr's law, a low ph would shift the curve to the right. Can someone explain? thanks
 

VPDcurt

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I don't take Kaplan but I took the Aug MCAT so here goes.

At high altitudes, the most significant response is hyperventilation. A consequence of hyperventilation is that CO2 is expired by the lungs and the arterial PCO2 decreases. So you have a decrease in PCO2, and the pH increases. The main point here is that there is an increase in the levels of 2,3 DPG in red blood cells caused by the hypoxemia at high altitudes. The increased levels of 2,3 DPG facilitate the delivery of O2 to the tissues so the curve will shift to the right.
 
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Nyphool

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this is still a bit shady. Are you saying that the increase in 2,3-DPG concentration which shifts the curve to the right supercedes the rise in pH which shifts the curve to the left? So there is a net shift to the right? thanks