Oxygen Dissociation Curve

Oxygen Dissociation Curve

Question 1. Draw a normal oxygen-haemoglobin dissociation curve. Explain Borh’s effect.
Answer:

Normal oxygen haemoglobin dissociation curve:

Bohr’s Effect:

• The relationship between the partial pressure of oxygen and the percentage saturation of haemoglobin with oxygen is explained graphically by oxygen haemoglobin dissociation curve.
• This curves shifts to right due to increase in partial pressure of carbon dioxide.
• In the tissues due to continuous metabolic activities, partial pressure of carbon dioxide increases in it and partial pressure of oxygen is less.
• Due to this pressure gradient, carbon dioxide moves from tissues to blood and oxygen moves from blood to tissues.
• Due to presence of carbon dioxide in blood, affinity of haemoglobin to oxygen decreases.
• As a result, the curve shifts to right.
• Thus, Bohr’s effect is loading of carbon dioxide to blood causing dissociation of oxygen at tissue level.

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Question 2. Transport of carbon dioxide.
Answer:

Carbon dioxide is transported by the blood from tissues to the alveoli in four ways.

1. As dissolved from -7%:

• Carbon dioxide diffuses into blood and dissolves in the fluid of plasma forming a simple solution and is transported.

2. As carbonic acid – negligible:

• Carbon dioxide enters the plasma and combines with water to form carbonic acid.Co₂+ H₂O H2CO₃
• Only 0.2% is transported in this form.

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3. As carbamino compounds -30%:

In plasma:

• Co₂ combines with plasma proteins and forms carbomino proteins.
• It is loose bond so can be easily released
• It is reversible reaction.

In RBCs:

• Co₂ combines with haemoglobin and forms carbhaemoglobin.
• It is also reversible process.

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4. As bicarbonates – 63%:

• From plasma, Co₂ enters the blood.
• Here, Co₂ combines with water present in RBC and forms carbonic acid in the presence of carbonic anhydrase enzyme.Co₂+H₂O → H₂CO₃
• Carbonic acid is unstable compound, so it reaily dissociated into bicarbonate and hydrogen ions.H₂CO₃ → HCO₃^– + H⁺
• By this, concentration of bicarbonate ion increases in RBCs.
• This leads to diffusion of bicarbonate from cell into plasma. Thus, Co₂ is transported in this form.