8.2.6—Bohr shift and its importance

The Bohr shift is the change in haemoglobin’s oxygen affinity caused by the higher carbon-dioxide conditions of respiring tissues. It shifts the oxygen dissociation curve to the right, so haemoglobin is less saturated at the same oxygen partial pressure.

• Demand signal: active respiring cells produce more carbon dioxide → carbonic acid dissociates and hydrogen ions are formed.
• Affinity change: hydrogen ions bind to haemoglobin and the higher CO2/H+ conditions reduce haemoglobin’s affinity for oxygen → oxygen is released more readily.
• Curve consequence: the dissociation curve shifts right → at the same tissue pO2, haemoglobin has a lower percentage saturation than it would under lower-CO2 conditions.
• Functional result: more oxygen dissociates from haemoglobin in the respiring tissue where demand is high → oxygen becomes available for cellular respiration.
• Lung-side recovery: in the lungs, CO2 is removed and the high-oxygen environment favours restoration of haemoglobin’s higher oxygen affinity, allowing oxygen loading for the next circuit.

Boundaries: the basic curve and cooperative binding belong to 4608; the partial-pressure location application belongs to 4609; the HCO3−/Cl− charge-balancing exchange is the chloride shift in 4606.

A right shift does not mean haemoglobin contains no oxygen or that oxygen cannot load in the lungs. It is a conditional affinity change linked to CO2/H+ conditions, not the chloride-ion exchange. Staff-only visual brief: paired low-CO2/high-affinity and high-CO2/right-shift curves with one shared pO2 read-off; do not generate or bind an image.