Which condition would cause a rightward shift of the oxyhemoglobin dissociation curve (Bohr effect)?

Which condition would cause a rightward shift of the oxyhemoglobin dissociation curve (Bohr effect)?

• A. Increased CO2 (or decreased pH)
• B. Decreased CO2
• C. Increased pH and decreased CO2
• D. No change in CO2 or pH

Answer: (A)

The main idea is the Bohr effect: hemoglobin’s oxygen affinity decreases when CO2 is high or pH is low, promoting oxygen release to tissues that are metabolically active. When CO2 levels rise, carbon dioxide entering red blood cells forms carbonic acid, which dissociates into H+ and bicarbonate. The increased hydrogen ions bind to hemoglobin and stabilize the low-affinity T state, so hemoglobin lets go of O2 more readily. This shifts the oxyhemoglobin dissociation curve to the right and increases the P50, meaning a higher oxygen tension is needed to saturate Hb, which aids delivery of O2 to tissues that need it. Conditions with lower CO2 or higher pH do the opposite: they raise Hb’s affinity for O2, shifting the curve to the left and facilitating loading in the lungs. A scenario with no change in CO2 or pH leaves the curve unchanged. So the rightward shift occurs with increased CO2 (or decreased pH).

The main idea is the Bohr effect: hemoglobin’s oxygen affinity decreases when CO2 is high or pH is low, promoting oxygen release to tissues that are metabolically active. When CO2 levels rise, carbon dioxide entering red blood cells forms carbonic acid, which dissociates into H+ and bicarbonate. The increased hydrogen ions bind to hemoglobin and stabilize the low-affinity T state, so hemoglobin lets go of O2 more readily. This shifts the oxyhemoglobin dissociation curve to the right and increases the P50, meaning a higher oxygen tension is needed to saturate Hb, which aids delivery of O2 to tissues that need it.

Conditions with lower CO2 or higher pH do the opposite: they raise Hb’s affinity for O2, shifting the curve to the left and facilitating loading in the lungs. A scenario with no change in CO2 or pH leaves the curve unchanged. So the rightward shift occurs with increased CO2 (or decreased pH).