The oxygen-haemoglobin dissociation curve is a core concept in physiology. It describes how readily haemoglobin binds oxygen in the lungs and releases it to tissues. It also complements practical interpretation of red blood cell count markers.
What is the oxygen-haemoglobin dissociation curve?
It is an S-shaped graph showing the relationship between:
At high pO2 (such as in the lungs), haemoglobin loads oxygen efficiently. At lower pO2 (such as in active tissues), haemoglobin unloads oxygen. These oxygen-state differences also explain why blood appears different shades in circulation.
Why is the curve S-shaped?
Haemoglobin shows cooperative binding. When one oxygen molecule binds, haemoglobin’s affinity for the next oxygen molecule increases. This creates the sigmoidal shape rather than a straight line. At the cellular level, this mechanism works with red blood cell membrane and shape adaptations.
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What is a right shift?
A right shift means haemoglobin has a lower affinity for oxygen, so oxygen is released to tissues more easily. Typical causes include:
This is often helpful during exercise or metabolic stress because tissues receive oxygen more readily.
What is a left shift?
A left shift means haemoglobin holds oxygen more tightly and releases less to tissues. Causes can include:
While loading in the lungs may remain efficient, tissue oxygen delivery can be relatively reduced. When symptoms suggest altered oxygen carrying capacity, clinicians often interpret this alongside haemoglobin reference ranges.
Why does this matter clinically?
Understanding curve shifts helps explain oxygen transport in respiratory illness, sepsis, anaemia, critical care, and exercise physiology. It supports interpretation of blood gas results and oxygen saturation trends. For broader investigation pathways, you can review options in the private blood test directory.
Key takeaway
The dissociation curve reflects a balance: haemoglobin needs to bind oxygen effectively in the lungs and release it in peripheral tissues. Right and left shifts alter that balance and can be physiologically adaptive or clinically significant depending on context.
Disclaimer
This article is for educational purposes only and does not replace professional medical assessment, diagnosis, or treatment.
Written Date: 30 September 2026 | Next Review Date: 30 September 2027