Oxygen Dissociation Curve: Definition, Function And Examples

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:41 PM IST

What Is the Oxygen Dissociation Curve?

The oxygen dissociation curve is central to describing how oxygen is associated with and discharged from haemoglobin in the blood. The theory related to this curve goes on to explain how, effectively, oxygen is supplied to tissues in our body and how carbon dioxide is removed.

Basics

Heme is a protein in the blood cells that carries oxygen from the air a person breathes to different parts of their body. The information about the relationship entered above between the partial pressure of oxygen and the percentage of haemoglobin saturated with oxygen is held within a graph.

Oxygen Binding Of Haemoglobin

Hemoglobin binds to oxygen cooperatively. The idea here is that, once an oxygen molecule has bound to the active site, this will increase its affinity for all the remaining sites to bind with the oxygen. This cooperative nature of binding with oxygen gives its characteristic sigmoid shape to the oxygen dissociation curve.

Oxygen Dissociation Curve: Definition, Function And Examples

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Factors Affecting The Shape Of The Oxygen Dissociation Curve:

Partial pressure of oxygen (pO2): This exerts the most marked influence on the curve. High pO2 in the lungs favours haemoglobin binding to oxygen, and values of low pO2 favour the release of oxygen in tissues.
pH: A decrease in pH: an increase in hydrogen ion concentrations—caused a decrease in affinity as P50 increased hence shifting the curves to the right; referred to as the Bohr effect.".
Carbon dioxide levels: Higher amounts of CO2 will shift the pH further right; thus, less binding with the oxygen is allowed by haemoglobin—meaning that then more oxygen is released.
Temperature: The curve shifts rightward as temperature increases. This has the effect of lowering haemoglobin's affinity for oxygen.
2,3-Bisphosphoglycerate: This is a molecule that binds with haemoglobin to decrease its affinity for oxygen. The net effect of this binding would be a shift to the right—favouring increased delivery of oxygen to tissues.

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Shifts In The Oxygen Dissociation Curve

Right Shift: Less haemoglobin affinity for oxygen; hence there will be an improved potential to give off oxygen to the tissues. Increased scavenge due to increased pCO2, higher temperatures, and decreased pH and increased 2,3-BPG.
Right Shift: A decreased affinity of haemoglobin to oxygen means a further enhancement in the ability of haemoglobin to give up oxygen to the tissues. This may happen with an increased pCO2, increased temperature, decreased pH, and increased 2,3-BPG.

P50 Value

It is the value of P50, which is the partial pressure required to produce 50 per cent saturation of haemoglobin. It happens to be a significant measure related to haemoglobin affinity for oxygen. An increase in P50 denotes a rightward shift as opposed to a decrease which signifies a leftward shift.

Physiological Relevance

Oxygen loading in the Lungs: An elevated pO2 ensures optimum loading of oxygen onto the haemoglobin of the lungs.
Oxygen unloading in the tissues: Low pO2 synergizes with other tissue factors to allow the offloading of oxygen from the Hb molecule, most effectively delivering it.
Adaptations: There are shifts in the oxygen-dissociation curve, as needed, to enable physical changes to adapt efficiently to the physical change for efficient transfer of oxygen, such as at high altitudes or during exercise.
Carbon Monoxide Poisoning: Carbon monoxide binds much more firmly to haemoglobin than oxygen and therefore decreases its oxygen-carrying capacity, shifting the curve to the left.
Sickle Cell Anemia: Abnormal haemoglobin of sick cell anaemia shall direct an abnormal oxygen dissociation curve and hence affect the delivery of oxygen.

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Frequently Asked Questions (FAQs)

1. Define the oxygen dissociation curve.

The oxygen dissociation curve is a graph showing the relationship of partial pressure of oxygen with per cent haemoglobin saturated with oxygen.

2. What are the factors that cause the oxygen dissociation curve to shift to the right?

Increased carbon dioxide, lower pH, increased temperature, and increased 2,3-BPG all produce a rightward shift. Therefore, the rightward shift gives haemoglobin a lesser affinity for oxygen.

3. What is the Bohr effect?

Changes in the oxygen affinity of haemoglobin due to changes in pH and carbon dioxide generally a shift to the right in the oxygen dissociation curve.

4. Why is the oxygen dissociation curve sigmoid in shape?

Because there is cooperative binding between the molecules of oxygen in haemoglobin, the binding of one molecule of oxygen increases the affinity for the binding of other molecules of oxygen.

5. What would anaemia do to the oxygen dissociation curve?

Anemia states have decreased total haemoglobin concentrations and therefore may shift the right oxyhaemoglobin dissociation curve, indicating a reduced affinity for oxygen and a reduced carrying capacity for it.

6. How does the oxygen dissociation curve relate to the concept of oxygen tension?

Oxygen tension, or partial pressure of oxygen (PO2), is represented on the x-axis of the oxygen dissociation curve. The curve shows how changes in oxygen tension affect the saturation of hemoglobin, illustrating the relationship between the physical measure of oxygen (tension) and its biological availability (saturation).

7. What is the relationship between the oxygen dissociation curve and the oxygen cascade?

The oxygen cascade describes the progressive decrease in oxygen partial pressure from the atmosphere to the mitochondria. The oxygen dissociation curve illustrates how hemoglobin facilitates oxygen transport along this cascade, maintaining adequate oxygen delivery despite decreasing PO2 levels.

8. What is the relationship between the oxygen dissociation curve and the concept of critical hemoglobin concentration?

The critical hemoglobin concentration is the level below which oxygen delivery to tissues becomes inadequate. The oxygen dissociation curve helps explain this concept by showing how oxygen content in the blood relates to PO2. As hemoglobin levels decrease, the curve effectively flattens, reducing the blood's ability to maintain adequate oxygen delivery, especially at lower PO2 levels.

9. How does the oxygen dissociation curve relate to the concept of tissue hypoxia?

The oxygen dissociation curve illustrates how changes in PO2 affect oxygen delivery to tissues. It helps explain why tissues can become hypoxic not only due to low PO2, but also due to shifts in the curve that affect hemoglobin's ability to release oxygen, such as in alkalosis or carbon monoxide poisoning.

10. How does the oxygen dissociation curve help explain the effectiveness of hyperbaric oxygen therapy?

The oxygen dissociation curve illustrates why hyperbaric oxygen therapy can be effective. By exposing patients to high pressures of pure oxygen, the PO2 in the blood can be increased far beyond normal levels. This pushes the curve to its upper limit, maximizing hemoglobin saturation and greatly increasing the amount of dissolved oxygen in the plasma.

11. Why is the oxygen dissociation curve S-shaped?

The S-shape of the oxygen dissociation curve reflects the cooperative binding of oxygen to hemoglobin. As more oxygen binds to hemoglobin, it becomes easier for additional oxygen molecules to attach, resulting in the steep middle portion of the curve. This shape allows for efficient oxygen loading in the lungs and unloading in the tissues.

12. How does the oxygen dissociation curve help explain the concept of oxygen reserve in the blood?

The sigmoid shape of the oxygen dissociation curve creates an oxygen reserve in the blood. At normal arterial PO2 levels, hemoglobin is nearly fully saturated (about 97-98%). This means that even if PO2 decreases slightly, the oxygen content of the blood remains relatively stable, providing a buffer against minor fluctuations in oxygen availability.

13. What is the relationship between the oxygen dissociation curve and the concept of tissue oxygenation?

The oxygen dissociation curve illustrates how oxygen is delivered to tissues. The steep portion of the curve in the physiological range allows for efficient oxygen unloading in the tissues. The curve helps explain how tissues can maintain adequate oxygenation even when blood flow or oxygen levels vary.

14. What is the significance of the upper plateau of the oxygen dissociation curve?

The upper plateau of the oxygen dissociation curve represents the point at which hemoglobin is nearly fully saturated with oxygen. This occurs at high PO2 levels, such as those found in the lungs. The plateau ensures that hemoglobin can be maximally loaded with oxygen even if there are small fluctuations in alveolar PO2.

15. How does the oxygen dissociation curve change in chronic obstructive pulmonary disease (COPD)?

In COPD, chronic hypoxemia and hypercapnia lead to a right shift in the oxygen dissociation curve. This adaptive response allows for increased oxygen unloading in the tissues, helping to compensate for the reduced oxygen uptake in the lungs.

16. What is the difference between oxyhemoglobin and deoxyhemoglobin?

Oxyhemoglobin is hemoglobin that has bound oxygen molecules, while deoxyhemoglobin is hemoglobin without bound oxygen. The transition between these two forms is represented by the oxygen dissociation curve, with oxyhemoglobin predominating at high PO2 and deoxyhemoglobin at low PO2.

17. What is the relationship between the oxygen dissociation curve and the oxygen-carrying capacity of blood?

The oxygen dissociation curve illustrates how much oxygen can be bound to hemoglobin at different partial pressures of oxygen. The oxygen-carrying capacity of blood is the maximum amount of oxygen that can be carried when hemoglobin is fully saturated. The curve shows how this capacity is utilized under varying physiological conditions.

18. How does the oxygen dissociation curve help explain the efficiency of the respiratory system?

The oxygen dissociation curve demonstrates the efficiency of the respiratory system by showing how hemoglobin can be nearly fully saturated at the relatively high PO2 levels in the lungs, and then release a significant amount of oxygen at the lower PO2 levels in the tissues. This allows for efficient oxygen loading and unloading with minimal changes in PO2.

19. How does the oxygen dissociation curve relate to the concept of oxygen saturation measured by pulse oximetry?

Pulse oximetry measures the percentage of hemoglobin saturated with oxygen, which corresponds to the y-axis of the oxygen dissociation curve. Understanding the curve helps interpret pulse oximetry readings, especially in conditions that may shift the curve and affect the relationship between PO2 and saturation.

20. How does the oxygen dissociation curve help explain the concept of venous reserve?

The venous reserve refers to the oxygen remaining in venous blood after tissue extraction. The oxygen dissociation curve shows that even at low PO2 levels typical of venous blood, hemoglobin retains some oxygen. This reserve can be mobilized during increased metabolic demand or reduced oxygen availability.

21. What is the significance of the P50 value on the oxygen dissociation curve?

The P50 value represents the partial pressure of oxygen at which hemoglobin is 50% saturated with oxygen. It is an important measure of hemoglobin's affinity for oxygen. A lower P50 indicates a higher affinity for oxygen, while a higher P50 indicates a lower affinity.

22. What is meant by the term "hemoglobin-oxygen affinity," and how is it represented on the oxygen dissociation curve?

Hemoglobin-oxygen affinity refers to how easily hemoglobin binds to or releases oxygen. On the oxygen dissociation curve, a higher affinity is represented by a left shift (hemoglobin holds onto oxygen more tightly), while a lower affinity is represented by a right shift (hemoglobin releases oxygen more readily).

23. What is the physiological significance of the lower plateau of the oxygen dissociation curve?

The lower plateau of the oxygen dissociation curve represents the point at which hemoglobin releases most of its bound oxygen. This occurs at low PO2 levels, such as those found in active tissues. The plateau ensures that tissues can continue to receive oxygen even when PO2 drops very low, providing a safety margin for oxygen delivery.

24. How does the oxygen dissociation curve change in anemia?

In anemia, the total amount of hemoglobin is reduced, but the shape of the oxygen dissociation curve remains largely unchanged. However, the body may compensate by increasing 2,3-BPG levels, which can cause a slight right shift in the curve to enhance oxygen delivery to tissues.

25. What is the role of allosteric regulation in shaping the oxygen dissociation curve?

Allosteric regulation refers to the influence of molecules binding to hemoglobin at sites other than the oxygen-binding sites. Factors like H+, CO2, and 2,3-BPG act as allosteric regulators, altering hemoglobin's structure and affinity for oxygen, which results in shifts of the oxygen dissociation curve.

26. What is the physiological importance of the steep portion of the oxygen dissociation curve?

The steep portion of the oxygen dissociation curve is crucial for efficient oxygen exchange. In the lungs, where oxygen partial pressure is high, small increases in PO2 result in large increases in oxygen saturation. Conversely, in the tissues, small decreases in PO2 lead to significant oxygen unloading, ensuring adequate oxygen delivery to cells.

27. How does altitude affect the oxygen dissociation curve?

At high altitudes, where the partial pressure of oxygen in the air is lower, the body adapts by shifting the oxygen dissociation curve to the right. This adaptation allows for more efficient oxygen unloading in the tissues, compensating for the reduced oxygen availability.

28. What is the role of 2,3-bisphosphoglycerate (2,3-BPG) in oxygen transport?

2,3-BPG is an organic phosphate that binds to hemoglobin and decreases its affinity for oxygen. By promoting oxygen release in the tissues, 2,3-BPG plays a crucial role in regulating oxygen delivery. Increased levels of 2,3-BPG cause a right shift in the oxygen dissociation curve.

29. How does exercise affect the oxygen dissociation curve?

During exercise, several factors contribute to a right shift in the oxygen dissociation curve:

30. What is meant by "oxygen loading" and "oxygen unloading" in relation to the oxygen dissociation curve?

"Oxygen loading" refers to the process of hemoglobin binding oxygen in the lungs, which occurs at the upper part of the curve where PO2 is high. "Oxygen unloading" refers to the release of oxygen from hemoglobin to the tissues, which occurs at the lower part of the curve where PO2 is low.

31. What does a right shift in the oxygen dissociation curve indicate?

A right shift in the oxygen dissociation curve indicates a decreased affinity of hemoglobin for oxygen. This means that hemoglobin releases oxygen more readily to the tissues, which can be beneficial in situations where increased oxygen delivery is needed, such as during exercise or in low-oxygen environments.

32. What factors can cause a right shift in the oxygen dissociation curve?

Several factors can cause a right shift in the oxygen dissociation curve, including:

33. How does the oxygen dissociation curve relate to the Bohr effect?

The Bohr effect describes the shift in the oxygen dissociation curve caused by changes in blood pH and CO2 levels. As pH decreases or CO2 levels increase, the curve shifts to the right, facilitating oxygen release in tissues where metabolic activity is high and CO2 production is increased.

34. How does fetal hemoglobin differ from adult hemoglobin in terms of the oxygen dissociation curve?

Fetal hemoglobin has a higher affinity for oxygen compared to adult hemoglobin. This results in a left-shifted oxygen dissociation curve for fetal blood, allowing the fetus to extract oxygen more efficiently from the mother's blood in the placenta.

35. What is myoglobin, and how does its oxygen dissociation curve compare to hemoglobin?

Myoglobin is an oxygen-binding protein found in muscle tissue. Its oxygen dissociation curve is hyperbolic rather than sigmoidal, and it has a higher affinity for oxygen than hemoglobin. This allows myoglobin to store oxygen in muscles and release it only when oxygen levels are very low.

36. What is the oxygen dissociation curve?

The oxygen dissociation curve is a graph that shows the relationship between the partial pressure of oxygen (PO2) in the blood and the percentage of hemoglobin saturated with oxygen. It illustrates how readily hemoglobin binds to or releases oxygen under different conditions.

37. What is the significance of the oxygen dissociation curve in understanding oxygen therapy?

The oxygen dissociation curve helps in understanding the effects of oxygen therapy. It shows that increasing inspired oxygen can significantly increase arterial PO2 and hemoglobin saturation. However, due to the curve's shape, there are diminishing returns at higher PO2 levels, informing decisions about appropriate oxygen administration.

38. What is the significance of the oxygen dissociation curve in understanding diving physiology?

The oxygen dissociation curve is crucial in understanding diving physiology. As divers descend and are exposed to higher pressures, the PO2 increases, potentially leading to oxygen toxicity. The curve helps explain why small increases in depth can result in large increases in dissolved oxygen and why careful monitoring of oxygen partial pressure is essential in diving.

39. What is the significance of the oxygen dissociation curve in understanding high-altitude adaptation?

The oxygen dissociation curve helps explain high-altitude adaptation. At high altitudes, where PO2 is lower, the curve initially shifts to the right to facilitate oxygen unloading. Over time, increased red blood cell production and other adaptations occur, allowing for more efficient oxygen uptake and delivery.

40. What is the relationship between the oxygen dissociation curve and the concept of venous admixture?

Venous admixture refers to the mixing of deoxygenated blood with oxygenated blood, which can occur in certain lung conditions. The oxygen dissociation curve helps explain why small amounts of venous admixture have little effect on arterial oxygen sat

41. How does carbon monoxide affect the oxygen dissociation curve?

Carbon monoxide binds to hemoglobin with much higher affinity than oxygen, forming carboxyhemoglobin. This shifts the oxygen dissociation curve to the left, reducing the ability of hemoglobin to release oxygen to the tissues and potentially leading to tissue hypoxia.

42. How does the oxygen dissociation curve change during pregnancy?

During pregnancy, the oxygen dissociation curve shifts slightly to the right due to increased 2,3-BPG levels and other physiological changes. This shift enhances oxygen delivery to the growing fetus and helps meet the increased metabolic demands of pregnancy.

43. How does the oxygen dissociation curve change in methemoglobinemia?

In methemoglobinemia, some hemoglobin is converted to methemoglobin, which cannot bind oxygen. This effectively shifts the oxygen dissociation curve to the left, increasing the affinity of the remaining normal hemoglobin for oxygen and impairing oxygen delivery to tissues.

44. What is the role of the oxygen dissociation curve in understanding acclimatization to high altitude?

The oxygen dissociation curve helps explain the process of acclimatization to high altitude. Initially, the curve shifts right to enhance oxygen unloading. Over time, increased erythropoiesis and other adaptations occur, effectively increasing the oxygen-carrying capacity of the blood and improving oxygen delivery at low PO2 levels.

45. How does the oxygen dissociation curve change in polycythemia?

In polycythemia, there is an increased number of red blood cells and thus more hemoglobin. While this doesn't change the shape of the oxygen dissociation curve for individual hemoglobin molecules, it increases the total oxygen-carrying capacity of the blood. The curve may shift slightly to the right due to increased 2,3-BPG levels often seen in polycythemia.

46. How does the oxygen dissociation curve change in sickle cell disease?

In sickle cell disease, the abnormal hemoglobin (HbS) has a lower affinity for oxygen, resulting in a right-shifted oxygen dissociation curve. This means that HbS releases oxygen more readily to tissues but may not load oxygen as efficiently in the lungs, contributing to the complex pathophysiology of the disease.

47. What is the significance of the oxygen dissociation curve in understanding carbon dioxide transport?

While primarily showing oxygen binding, the oxygen dissociation curve also relates to CO2 transport. As hemoglobin releases oxygen in the tissues, it becomes better at carrying CO2 (the Haldane effect). This interplay between oxygen and CO2 transport is reflected in the shifts of the curve caused by changes in CO2 levels.

48. How does the oxygen dissociation curve help explain the concept of oxygen debt during exercise?

The oxygen dissociation curve illustrates how oxygen delivery to muscles increases during exercise. The right shift of the curve due to increased temperature, CO2, and acidity allows for greater oxygen unloading. However, when oxygen demand exceeds supply, an oxygen debt accumulates, which is repaid during recovery as the curve shifts back to its resting position.