Oxygen Dissociation Curve: Definition, Function And Examples

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 of Oxygen Binding

The basics of oxygen binding is discussed below:

Hemoglobin Structure & Function

Heme is a protein in the red 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.

Cooperative Binding

Hemoglobin binds to oxygen cooperatively. Once an oxygen molecule has bound to the active site, this will increase the 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.

Factors Affecting The Oxygen Dissociation Curve

The factors affecting the oxygen dissociation curve are:

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 (Bohr Effect)

A decrease in pH means 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.

Shifts In The Oxygen Dissociation Curve

The shift in the oxygen dissociation curve is discussed below:

Right Shift (↓ affinity, ↑ O₂ delivery)

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.

Left Shift (↑ affinity, ↓ O₂ delivery)

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 — Indicator of Affinity

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 of Oxygen Dissociation Curve

The physiological relevance of oxygen dissociation curve is discussed below:

Oxygen loading in Lungs

An elevated pO2 ensures optimum loading of oxygen onto the haemoglobin of the lungs.

Oxygen unloading in 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.

Pathological Relevance

Carbon monoxide binds much more firmly to haemoglobin than oxygen and therefore decreases its oxygen-carrying capacity, shifting the curve to the left.

Abnormal haemoglobin of sickle cell anaemia shall direct an abnormal oxygen dissociation curve and hence affect the delivery of oxygen.

Oxygen Dissociation Curve NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Factors affecting the oxygen dissociation curve

• Shifts in the oxygen dissociation curve

Practice Questions for NEET

Q1. At high temperatures, the Hb will be less likely to stick to the oxygen and release it into the tissues, this causes the oxygen dissociation curve to shift to

1. Left

2. Right

3. No movement

4. Slightly left then right

Correct answer: 2) Right

Explanation:

DPG (2,3-diphosphoglycerate) and temperature both shift the oxygen dissociation curve to the right, promoting oxygen release from haemoglobin to tissues. DPG binds to haemoglobin, reducing its affinity for oxygen, especially at lower oxygen concentrations. Increased temperature also decreases haemoglobin's affinity for oxygen, enhancing oxygen delivery during conditions like exercise or fever. These changes help tissues receive more oxygen when metabolic demand is high.

At high temperatures, the Hb will be less likely to stick to the oxygen and release it into the tissues. The curve shifts to the right when the temperature increases.

Hence, the correct answer is option 2) Right.

Q2. Read the following statements

STATEMENT i): the decrease in 2,3 DPG concentration within the red cell shifts the curve to the left.

STATEMENT ii): lower temperature causes a leftward shift in the oxygen dissociation curve.

Choose the correct option:

1. Statement (i) is correct and statement (ii) is incorrect

2. Statement (i) is incorrect and statement (ii) is correct

3. Both statements are wrong

4. Both statements are correct

Correct answer: 4) Both statements are wrong

Explanation:

Explanation of statement i) : Statement i) is correct because The position of the oxygen dissociation curve (ODC) is modulated by 2,3-diphosphoglycerate (2,3-DPG). Decreases in 2,3-DPG concentration within the red cell shift the curve to the left, whereas increases in concentration cause a shift to the right of the ODC.

Explanation of statement ii): Statement ii) is also correct because The effect of temperature on the curve is relatively straightforward. Oxygen unloading is favored at higher temperatures which will cause a rightward shift. On the other hand, lower temperatures will cause a leftward shift in the dissociation curve.

Hence, the correct answer is option 4) Both statements are correct.

Q3. Which of the following will shift the Oxygen dissociation curve to the left?

a) Increase hydrogen ions

b) Increase 2,3-DPG

c) Decrease CO2

d) Decrease Temperature

1. a and b

2. c and d

3. a and c

4. b and d

Correct answer: 2) c and d

Explanation:

Both of these elements would cause the oxygen dissociation curve to move to the left increasing haemoglobin's affinity for oxygen and its ability to hold onto oxygen.

Decrease in CO2: The blood becomes less acidic (pH rises) when CO2 levels are lower which raises haemoglobin's affinity for oxygen and causes the curve to move to the left.

Temperature decrease: The curve moves to the left as a lower temperature also improves haemoglobin's affinity for oxygen.

The oxygen dissociation curve is shifted to the right by increases in 2,3-DPG (b) a byproduct of metabolism and hydrogen ions (a) which raise blood acidity. Haemoglobin can more easily provide oxygen to tissues that require it as a result.

Hence, the correct answer is option 2) c and d.

Also Read:

• MCQs on Oxygen Dissociation Curve

• Thoracic Cavity

• Lung Capacity and Lung Volumes

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