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Haemoglobin

4 x Haem group + 4 x Polypeptide chain

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The Bohr Effect

100%

% saturation

of

haemoglobin

partial pressure of O2 (mmHg)

Plateau:

Haemaglobin has a high affinity for O2so is

highly saturated even if there is not much O2

Makes the haemaglobin load up with O2 in

lung

Steep slope:

A small drop in the amount of O2means the haemaglobin

has a much lower affinity for O2

The haemaglobin is less saturated with oxygen as it gives itup to the tissues more easily.

This means the haemaglobin is highly effective in uptaking large amount of O2from the lungs but release it so easily to the tissue cells

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Bohr effect the effect of CO2 on haemoglobin

% saturation of

haemoglobin

partial pressure of O2 (mmHg)

Higher CO2 e.g. tissue cells

curve shift to the right

in actively respiring tissue cells, O2 is more easily released by haemoglobin !

haemoglobin has a lower

affinity to O2

Lower CO2 e.g. in lung curve shift to the left

haemoglobin has a higheraffinity to O2

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Oxygen dissociation curve: Haemoglobin VS Myoglobin

% saturation of

haemoglobin

partial pressure

of O2 (mmHg)

Haemoglobin

Myoglobin stores O2 in muscles and release it only whenthe O

2

partial pressure is very low.

Myoglobin

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Oxygen dissociation curve:

Foetal VS Maternal

% saturation of

haemoglobin

partial pressure

of O2 (mmHg)

Maternal

Foetal haemoglobin has higher affinity to O2 so as obtain

O2 from maternal blood in the placenta.

Foetal

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Transport of carbon dioxide

CO2 is carried by your blood in three ways:

5% carried in solution in the plasma as CO2

10% combines with the haemoglobin to form

carbamino-haemoglobin

85% is carried in red blood cells as hydrogen

carbonate: HCO3-

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Formation of hydrogen carbonate CO2diffuses from tissues into red blood cells.

The RBCs contain an enzyme called carbonic anhydrase

which catalyses the reaction between CO2and water toform carbonic acid:

CO2 + H2O H2CO3

Carbonic acid dissociates into negatively charged

hydrogen carbonate and positively charged hydrogen ions:H2CO3 H+ + HCO3

-

The hydrogen ions (H+) increase the acidity of the bloodand combine with Haemoglobin to give haemoglobinic acid.

This decreases the affinity of haemoglobin to oxygen soit gives it up to the tissues (the Bohr effect)

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Formation of hydrogen carbonate The build up of hydrogen carbonate ions causes

them to diffuse out of the RBC leaving the insideof the RBC positively charged.

In order to balance this electric charge, chlorideions diffuse into the RBCs from the plasma this isknown as the chloride shift.

At the lungs, all these reactions are reversed: The hydrogen carbonate and hydrogen ions

recombine releasing CO2.

The chloride shift is reversed. Carbamino-haemoglobin breaks down to release

CO2.