Oxygen Transport and Oxygen Dissociation Curve MCQ

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Oxygen Transport and Oxygen Dissociation Curve

Blood is the medium of transport for $O_{_{2}}$ and $CO_{_{2}}$ .
About 97 percent of $O_{_{2}}$ is transported by RBCs in the blood.
The remaining 3 percent of $O_{_{2}}$ is carried in a dissolved state through the plasma.
Haemoglobin is a red coloured iron-containing pigment present in the RBCs.
$O_{_{2}}$ can bind with haemoglobin in a reversible manner to form oxyhaemoglobin. This is called O2-Hb association.
Each haemoglobin molecule can carry a maximum of four molecules of $O_{_{2}}$ .
Binding of oxygen with haemoglobin is primarily related to the partial pressure of $O_{_{2}}$ .
$pO_{_{2}}$ is high in alveoli so association occurs while at the tissues, the $pO_{_{2}}$ decreases which cause dissociation of oxygen.
The partial pressure of $CO_{_{2}}$ , hydrogen ion concentration and temperature are the other factors which can interfere with this binding.
A sigmoid curve is obtained when the percentage saturation of haemoglobin with $O_{_{2}}$ is plotted against the $pO_{_{2}}$ .
This curve is called the Oxygen dissociation curve.
This curve is highly useful in studying the effect of factors like $pCO_{_{2}}$ , H+ concentration, etc, on the binding of $O_{_{2}}$ with haemoglobin.
In the alveoli, there is
- high $pO_{_{2}}$
- low $pCO_{_{2}}$
- lesser H+ concentration
- high pH
- lower temperature
- low 2,3-BPG
These factors are all favourable for the formation of oxyhaemoglobin.
In the tissues, there is
- low $pO_{_{2}}$
- high $pCO_{_{2}}$
- high H+ concentration
- low pH
- higher temperature
- high 2,3-BPG
2,3-BPG is Bisphophoglyceric acid. It lowers the affinity of oxygen to Hb and thus it is more near the tissues. This compound thus helps is dissociation of oxyheamoglobin.
These conditions are favourable for dissociation of oxygen from oxyhaemoglobin.
This clearly indicates that $O_{_{2}}$ gets bound to haemoglobin in the lung surface and gets haemoglobin in the lung surface and gets dissociated at the tissues.
Every 100 ml of oxygenated blood can deliver around 5 ml of $O_{_{2}}$ to the tissues under normal physiological conditions.

Effect of DPG and Temperature on Oxygen Dissociation Curve

2,3-diphosphoglycerate is formed during glycolysis.
It enters the plasma when produced in excess and drifts into the RBCs to bind to deoxyhemoglobin.
Hence, the formation of oxyhemoglobin is not allowed and the curve shifts to the right.
The concentration of BPG increases during the exercise.
Tissues have a higher metabolic rate and therefore produce more thermal energy as a water by-product.
This results in an increase in the temperature of the surrounding blood plasma.
At high temperature, the Hb will be less likely to stick to the oxygen and releases it into the tissues. `
The curve shifts to the right when the temperature increases.