Explain the oxyhaemoglobin dissociation curve and the factors that may alter it.
Marks were awarded for an appropriate curve with values, an explanation of the nature of
positive cooperatively and notes on those factors causing changes in the p50 or "shifts” in the
Most candidates were able to provide the required sigmoid shaped curve with appropriate key
value points (p50, venous and arterial points). Better candidates were able to identify p50 as a
measure of avidity or affinity for oxygen and commented on T- Tense and R- Relaxed states,
the role and production of 2,3 DPG , binding to the beta chains (nature of the lack effect on
foetal haemoglobin). Describing the mechanisms associated with factors shifting the curve and
commenting on changes in oxygen content over the steep and flatter parts of the curves gained
additional marks. Candidates are reminded to answer the question asked - no marks were
awarded for a description of dissolved oxygen delivery. Some answers confused the Bohr and
The oxyhaemoglobin dissociation curve is a sigmoidal relationship between the partial pressure of oxygen and the oxygen saturation of haemoglobin:
The following physiological factors influence the affinity of hemoglobin for oxygen:
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- this is an English translation of the original article, which was beautifully titled "Über einen in biologischer Beziehung wichtigen Einfluss, den die Kohlensäurespannung des Blutes auf dessen Sauerstoffbindung übt".
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