What is the role of 2,3-BPG in altitude adaptation?

What is the role of 2,3-BPG in altitude adaptation?

• A. Shifts the oxygen-hemoglobin dissociation curve to the left, making unloading harder.
• B. Decreases the affinity of hemoglobin for oxygen in tissues.
• C. Shifts the oxygen-hemoglobin dissociation curve to the right, facilitating O2 unloading.
• D. Increases hemoglobin concentration directly.

Answer: (C)

2,3-BPG works by binding to deoxyhemoglobin and stabilizing the T (tense) state, which lowers hemoglobin’s affinity for oxygen. In altitude, chronic low oxygen levels cause red blood cells to produce more 2,3-BPG. That increase shifts the oxygen-hemoglobin dissociation curve to the right, meaning hemoglobin releases oxygen more readily to tissues. This helps maintain tissue oxygen delivery despite the reduced oxygen coming into the lungs. The lungs can still load oxygen effectively because the alveolar PO2 is high, so oxygen binding remains adequate even with the rightward shift.

So, the best description is that 2,3-BPG shifts the curve to the right, facilitating O2 unloading. It doesn’t directly raise hemoglobin concentration—that’s a separate polycythemia response—and left-shifting the curve would actually hinder oxygen unloading, which would be disadvantageous at high altitude.