- In haemoglobin affinity for oxygen increases when there is
(1) High H+ (2) High pCO2
(3) High temperature (4) High 2,3 BPG
Introduction
The affinity of hemoglobin (Hb) for oxygen (O₂) determines how readily it binds oxygen in the lungs and releases it in tissues. This affinity is influenced by various factors that shift the oxygen-hemoglobin dissociation curve to the right or left, altering oxygen delivery to tissues.
Factors Affecting Hemoglobin’s Oxygen Affinity
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Increase in H⁺ concentration (Low pH) (High acidity):
Low pH reduces Hb’s affinity for oxygen, shifting the curve right, facilitating oxygen release in tissues (Bohr effect). -
Increase in pCO₂:
Elevated carbon dioxide also decreases oxygen affinity by forming carbaminohemoglobin and lowers pH, causing a rightward shift and enhancing oxygen unloading. -
Increase in Temperature:
Higher temperatures weaken the Hb-O₂ bond, shifting the curve right and reducing affinity. -
Increase in 2,3-Bisphosphoglycerate (2,3-BPG):
2,3-BPG binds to deoxygenated Hb and decreases Hb oxygen affinity, shifting the curve to the right, aiding oxygen release in tissues.
What Increases Hemoglobin’s Oxygen Affinity? (Leftward Shift)
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Decrease in H⁺ (higher pH, alkalosis)
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Decrease in pCO₂
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Decrease in temperature
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Decrease in 2,3-BPG
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Presence of fetal hemoglobin or carbon monoxide (artificially increases affinity but harms oxygen delivery)
Correct Answer to the Query
Given options affecting hemoglobin’s affinity for oxygen:
Factor Effect on Hb-O₂ Affinity (1) High H⁺ (Low pH) Decreases affinity (right shift) (2) High pCO₂ Decreases affinity (right shift) (3) High temperature Decreases affinity (right shift) (4) High 2,3 BPG Decreases affinity (right shift) None of the options directly increase affinity. Since the question asks for factors increasing affinity, each listed actually decreases it.
Thus, the correct interpretation is:
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All options reduce affinity, so none increases it.
If the question implies selecting which factors affect affinity (usually by decreasing it):
Answer choice that does not increase affinity but reduces it is often considered.
Explanation
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The Bohr effect is crucial in releasing oxygen where it is needed (high CO₂, low pH, high temperature, high 2,3-BPG occur in metabolically active tissues).
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These factors make hemoglobin less “sticky” to oxygen, facilitating oxygen release.
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A left shift would indicate increased affinity, which is opposite to the factors described.
Summary Table
Factor Effect on Oxygen Affinity Curve Shift High H⁺ (Acidosis) Decreases affinity Right High pCO₂ Decreases affinity Right High temperature Decreases affinity Right High 2,3-BPG Decreases affinity Right
Conclusion
None of the factors listed increase hemoglobin’s oxygen affinity; instead, all contribute to its decrease.
If forced to select based on the question’s wording, none precisely fit “increase”; however, by exclusion:
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Increased Hb affinity occurs with low H⁺, low CO₂, low temperature, reduced 2,3-BPG (not listed).
Therefore, none of the above increase affinity; all decrease it.
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