Oxygen – Dissociation curve:

When percentage saturation of hemoglobin with oxygen (O₂) ,  is  plotted against the partial pressure of oxygen (Po₂), in atmosphere. This plot is called O₂-HB Dissociation curve. This Curve is always sigmoid.

Reason for its sigmoid pattern: When Po₂ increases, more O₂ will binds with HB and blood 97% oxygenated and leaves the lungs but due to more O₂ pressure, hemoglobin become less after sometimes and no increase in curve.

Hemoglobin is red colored Iron pigment in RBCs of blood. One HB molecule can bind with 4 O₂ molecules.

Binding of oxygen with hemoglobin to form oxy-hemoglobin depends upon:-

1. Partial pressure of O₂
2. Partial pressure of Co₂
3. Hydrogen ion concentration
4. Temperature:

• In alveoli, there is high Po₂, Lesser H⁺ concentration and low temperature. These factors are favorable for the formation of oxy-hemoglobin.
• In tissues, there is low Po₂, high PCo₂ , high H⁺ concentration and high temperature. These conditions are favorable for the dissociation of O₂ from oxy-hemoglobin (removal).
• Color of deoxygenated blood: dark purplish red.Color of oxygenated blood:  Red.

Effect of PO₂ on oxygen Transport:-

As PO₂ in blood increases, then more oxygen will bind with hemoglobin (more oxy-hemoglobin will form). It leads to rightward shift of oxygen –HB dissociation curve. Here, hemoglobin become less after a limit. So it starts loosing O₂ and passes it to tissues. It is called Bohr’s effect. It plays a crucial role in increasing oxygenation of blood in lungs and release of O₂ in tissues.

 

Haldane effect:- It describes, how oxygen concentration determines heamoglobin affinity towards Co₂.

1. Like, In high O₂ Concentration, O₂ binds with heamoglobin and prevent the Co₂  to do so.
2. And in low O₂ Concentration Co₂ binds with heamoglobin.

In both cases, O₂ is responsible for changes in Co₂ concentration in blood. ( Deoxygenation of blood increases its ability to carry Co₂ )

Bohr’s effect:- It defines how, Co₂ and its ions concentration controls the affinity of HB to bind with O₂.

1. High Co₂ and H⁺ concentration decreases O₂ affinity to  bind with HB.
2. Low Co₂ and H⁺ concentration increases O₂ affinity to bind with HB.

For example:- In working muscles, O₂ level is low but Co₂ and H⁺ level is high. So, muscles now get oxygen from oxygenated blood.