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During physical exercise, a large amount of oxygen is delivered to the active muscles by many physiological adjustments, including a change in the P₅₀ value (which is determined by P₀₂ at which hemoglobin is half-saturated with oxygen).

The following proposed statements explain the mechanism of change in P₅₀ during exercise:

A.P₅₀ is increased during exercise as the temperature rises in active muscles.
B.During exercise, metabolites accumulate in the active muscles, resulting in higher pH that increases P₅₀.
C.P₅₀ is increased during exercise as CO₂ is decreased in active muscles.
D.An increase in 2,3-DPG has been reported in non-trained persons within 60 min of exercise, resulting in higher P₅₀.

Which one of the following options represents the correct combination of the above statements?

Correct option is D

P₅₀ (Oxygen Dissociation Parameter) refers to the partial pressure of oxygen (P₀₂) at which hemoglobin is 50% saturated with oxygen. A higher P₅₀ indicates a lower affinity of hemoglobin for oxygen, meaning oxygen is more readily released to tissues, which is crucial during exercise.

Statement A: "P₅₀ is increased during exercise as the temperature rises in active muscles."- Correct

• During exercise, muscle temperature increases due to increased metabolic activity.
• Higher temperature decreases hemoglobin’s affinity for oxygen, shifting the oxygen dissociation curve to the right and increasing P₅₀.
• This allows more oxygen to be delivered to the muscles.

Statement B: "During exercise, metabolites accumulate in the active muscles, resulting in higher pH that increases P₅₀." - Incorrect

• Exercise leads to the accumulation of metabolites such as lactic acid and CO₂, which lower pH (acidosis).
• A lower pH actually increases P₅₀, not a higher pH.
• Since this statement incorrectly claims that higher pH increases P₅₀, it is incorrect.

Statement C: "P₅₀ is increased during exercise as CO₂ is decreased in active muscles." - Incorrect

• During exercise, CO₂ increases due to cellular respiration.
• Increased CO₂ leads to the Bohr effect, where hemoglobin releases more oxygen, increasing P₅₀.
• Since the statement incorrectly claims that P₅₀ increases due to decreased CO₂, it is incorrect.

Statement D: "An increase in 2,3-DPG has been reported in non-trained persons within 60 min of exercise, resulting in higher P₅₀."  - Correct

• 2,3-DPG (2,3-diphosphoglycerate) is a metabolite that binds to hemoglobin and reduces its oxygen affinity.
• During exercise, particularly in non-trained individuals, 2,3-DPG levels rise, shifting the oxygen dissociation curve to the right and increasing P₅₀.
• This helps release more oxygen to muscles, aiding performance.

Information Booster:

1. Factors that Increase P₅₀ (Rightward Shift of the Oxygen Dissociation Curve):

   • Increased temperature (muscle activity during exercise).
   • Increased CO₂ (Bohr effect).
   • Decreased pH (acidosis) due to lactic acid buildup.
   • Increased 2,3-DPG (adaptation to prolonged exercise or hypoxia).

2.  Rightward Shift is Beneficial During Exercise

   • Hemoglobin has a lower affinity for oxygen, meaning more oxygen is released to muscles.
   • This improves oxygen delivery for aerobic respiration in active tissues.

3. Bohr Effect and CO₂ in Exercise:

   • More CO₂ is produced in muscle cells.
   • CO₂ lowers pH, leading to increased oxygen unloading (higher P₅₀).
   • This contradicts statement C, which incorrectly states that CO₂ decreases P₅₀.

4. Role of 2,3-DPG in Exercise:

   • 2,3-DPG increases under prolonged exercise or hypoxia, helping to unload oxygen from hemoglobin more efficiently.
   • More prominent in non-trained individuals since trained athletes have more efficient oxygen transport.