Leftward shift of the oxyhemoglobin dissociation curve is produced by which condition?

Leftward shift of the oxyhemoglobin dissociation curve is produced by which condition?

• A. Acidosis
• B. Hyperthermia
• C. Alkalosis
• D. Increased 2,3-DPG

Answer: (C)

A leftward shift of the oxyhemoglobin dissociation curve means hemoglobin has a higher affinity for oxygen, so it holds onto O2 more tightly and is less willing to release it to tissues at a given partial pressure of oxygen. Factors that raise pH (alkalosis), lower temperature, or reduce 2,3-DPG favor this higher affinity, shifting the curve to the left. Alkalosis increases blood pH, which reduces hydrogen ion concentration and diminishes the Bohr effect. With fewer protons around, hemoglobin’s affinity for oxygen increases, moving the curve left. Lower levels of 2,3-DPG also promote tighter binding of O2 to hemoglobin, reinforcing the leftward shift. In practice, this means better oxygen loading in the lungs but potentially poorer oxygen unloading to tissues. In contrast, acidosis and hyperthermia increase hydrogen ion concentration and temperatures, promoting the Bohr effect and stabilizing the deoxygenated (T) state, which shifts the curve to the right, decreasing O2 affinity. Increased 2,3-DPG lowers affinity and shifts the curve to the right as well. Thus alkalosis is the condition that causes a leftward shift of the curve.

A leftward shift of the oxyhemoglobin dissociation curve means hemoglobin has a higher affinity for oxygen, so it holds onto O2 more tightly and is less willing to release it to tissues at a given partial pressure of oxygen. Factors that raise pH (alkalosis), lower temperature, or reduce 2,3-DPG favor this higher affinity, shifting the curve to the left.

Alkalosis increases blood pH, which reduces hydrogen ion concentration and diminishes the Bohr effect. With fewer protons around, hemoglobin’s affinity for oxygen increases, moving the curve left. Lower levels of 2,3-DPG also promote tighter binding of O2 to hemoglobin, reinforcing the leftward shift. In practice, this means better oxygen loading in the lungs but potentially poorer oxygen unloading to tissues.

In contrast, acidosis and hyperthermia increase hydrogen ion concentration and temperatures, promoting the Bohr effect and stabilizing the deoxygenated (T) state, which shifts the curve to the right, decreasing O2 affinity. Increased 2,3-DPG lowers affinity and shifts the curve to the right as well.

Thus alkalosis is the condition that causes a leftward shift of the curve.