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Objectives for today:

describe and explain the significance of the dissociationcurves of adult oxyhaemoglobin at different carbon dioxide

levels (the Bohr effect). explain the significance of the different affinities of foetal

haemoglobin and adult haemoglobin for oxygen.

Syllabus: 1.2.2 m & nHomework: continue with revision for your January exams.

Now:

http://www.cellsalive.com/mitosis.htm

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100%

%sa

turationofh

aemaglobin

partial pressure of O2 (mmHg)

Plateau:Haemaglobin has a highaffinity for O2so is highly saturated andtherefore loads up with O2 in the lungs.

Steep slope:

A small drop in the amount of O2means thehaemaglobin has a much lower affinity for O

2

The haemaglobin is less saturated with oxygen sogives it up to the tissues more easily.

Why does haemaglobin load lots of O2 at the lungs butrelease it so easily at the tissues?

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CO2 is carried by your blood in threeways:

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 to form carbonic acid:

CO2 + H2O H2CO3

Carbonic acid dissociates into negatively chargedhydrogen carbonate & positively charged hydrogen ions:

H2CO3 H+ + HCO3

-

The hydrogen ions (H+) lower the pH of the blood /

make it more acidic and combine with haemoglobin togive haemoglobinic acid.

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

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Bohr effect the effect of CO2 on haemaglobin

%s

aturatio

nofhaemag

lobin

partial pressure of O2 (mmHg)

Lower CO2 e.g. in lungs curve shift to theleft

haemaglobin has ahigher affinityfor O2

Higher CO2e.g. tissues

curve shift to theright

haemaglobin has aloweraffinityfor O2

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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 inside of the RBC

positively charged.

In order to balance this electric charge, chloride ions

diffuse into the RBCs from the plasma this is known

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

haemaglobin and CO2.

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Oxygen dissociation curve: Foetal vs. Maternal

%s

aturationofhaemo

globin

partial pressure of O2 (mmHg)

Foetal haemaglobin curve shift to theleft

higher affinityfor O2

Maternal haemaglobin curve shift to theright

lower affinityfor O2 gives up O2 to foetal

haemaglobin at placenta

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And now:

1. Read p.64-67 in the purple text books and p.82-84in the green books.

2. Try the exam Qs. Check your answers carefullyagainst the mark scheme have you used the samekey words and phrases? Ask me to check what youhave written.

Extension:

Try the Qs on p.65 & 67 of the purple books.Answers on p.239.