The Bohr Shift Is How Carbon Dioxide Drives Oxygen Release in Respiring Tissues
Definition
Bohr Shift
- The Bohr shift (or Bohr effect) describes how haemoglobin’s affinity for oxygen decreases in the presence of high levels of carbon dioxide (CO₂) or in acidic environments (lower pH).
- The Bohr Effect describes how increased carbon dioxide levels and lower pH in active tissues reduce haemoglobin’s affinity for oxygen, promoting oxygen release.
- This adaptation ensures that oxygen delivery increases in tissues where it’s needed the most—such as during aerobic respiration.
How the Bohr Shift Works
1. Carbon Dioxide and pH Reduction
- Reaction in Red Blood Cells: $$ \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}^+ + \text{HCO}_3^- $$
- Carbon dioxide combines with water, forming hydrogen ions (H⁺) and hydrogen carbonate ions (HCO₃⁻).
- The H⁺ ions lower the blood’s pH (making it more acidic), which reduces haemoglobin’s affinity for oxygen.
- In active muscles, where carbon dioxide concentration is high, the pH drops to around 7.2.
- In the lungs, where carbon dioxide levels are low, the pH is closer to 7.4, promoting oxygen binding to haemoglobin.
