The compensatory shift toward normal in chronic respiratory alkalosis is mediated by changes in which erythrocyte metabolite?

The compensatory shift toward normal in chronic respiratory alkalosis is mediated by changes in which erythrocyte metabolite?

• A. Hemoglobin
• B. 2,3-DPG
• C. ATP
• D. NADH

Answer: (B)

In red blood cells, the molecule 2,3-DPG (2,3-BPG) modulates how tightly hemoglobin holds onto oxygen. In chronic respiratory alkalosis, the blood pH is elevated, which tends to make hemoglobin bind oxygen more tightly and shift the oxygen–hemoglobin dissociation curve to the left. To offset this and preserve tissue oxygen delivery, erythrocytes increase 2,3-DPG levels. The higher 2,3-DPG binds to deoxygenated hemoglobin and lowers its affinity for oxygen, shifting the curve to the right and promoting more oxygen release at the tissues. This compensatory adjustment helps normalize oxygen delivery despite the alkalemia. 2,3-DPG is the mediator here because it directly alters hemoglobin’s affinity for oxygen. Hemoglobin itself is the carrier, not a metabolite; ATP and NADH are energy-related molecules and do not specifically drive this O2 affinity shift in this context.

In red blood cells, the molecule 2,3-DPG (2,3-BPG) modulates how tightly hemoglobin holds onto oxygen. In chronic respiratory alkalosis, the blood pH is elevated, which tends to make hemoglobin bind oxygen more tightly and shift the oxygen–hemoglobin dissociation curve to the left. To offset this and preserve tissue oxygen delivery, erythrocytes increase 2,3-DPG levels. The higher 2,3-DPG binds to deoxygenated hemoglobin and lowers its affinity for oxygen, shifting the curve to the right and promoting more oxygen release at the tissues. This compensatory adjustment helps normalize oxygen delivery despite the alkalemia.

2,3-DPG is the mediator here because it directly alters hemoglobin’s affinity for oxygen. Hemoglobin itself is the carrier, not a metabolite; ATP and NADH are energy-related molecules and do not specifically drive this O2 affinity shift in this context.