What is Oxygen–Hemoglobin Dissociation Curve and Factors Affecting It

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Detailed Solution

The oxygen–hemoglobin dissociation curve is an S-shaped (sigmoid) graph showing the relationship between the partial pressure of oxygen (pO₂) and the percentage saturation of hemoglobin with oxygen.

Key points of the curve:

At high pO₂ (lungs, ~100 mm Hg): Hemoglobin is ~98% saturated with oxygen.
At low pO₂ (tissues, ~40 mm Hg): Hemoglobin releases oxygen, saturation drops to ~75%.
The curve is sigmoidal due to cooperative binding—each oxygen molecule binding increases hemoglobin’s affinity for the next.

Factors shifting the curve:

Condition	Effect on Curve	Explanation
↑ CO₂ (high pCO₂)	Right shift	Reduces O₂ affinity — Bohr Effect.
↓ pH (acidic)	Right shift	Promotes O₂ release to tissues.
↑ Temperature	Right shift	Increases O₂ delivery during exercise.
↓ CO₂ / ↑ pH	Left shift	Higher O₂ affinity in lungs.

Bohr Effect: The tendency of hemoglobin to release more oxygen at high CO₂ concentration and lower pH levels. This ensures efficient oxygen unloading at metabolically active tissues.

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