How Oxygen is carried Round the Body by Haemoglobin

Haemoglobin Saturation

Dissociation Curves

Fetal Haemoglobin


How Carbon Dioxide Concentration Affects Oxygen Unloading

The Bohr Shift

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  • Created by: Benedicta
  • Created on: 07-01-11 13:59
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28 December 2010
Oxygen is carried Round the Body by Haemoglobin
Red blood cells contain haemoglobin (Hb)
Is a large protein with quaternary structure ­ made up of 4 polypeptide chains
Each chain has haem group which contains iron and gives haemoglobin red colour
Has high affinity for oxygen ­ each molecule can carry 4 oxygen molecules
In lungs, oxygen joins to iron in haemoglobin to form oxyhaemoglobin
Reversible reaction ­ when oxygen leaves oxyhaemoglobin (dissociates from it) turns back to
Hb + 4O2 HbO8
Affinity for oxygen means the tendency to combine with oxygen
Haemoglobin Saturation Depends on the Partial Pressure of Oxygen
Measure of oxygen concentration (pO2)
Greater concentration of dissolved oxygen in cells, higher the partial pressure
pCO2 is a measure of the concentration of CO2 in a cell
Haemoglobin's affinity for O2 varies depending on pCO2 (Oxygen loads onto haemoglobin to
form oxyhaemoglobin where there's high pO2. Oxyhaemoglobin unloads its O2 where there's
lower pO2)
Alveoli have high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin
Respiring cells use up oxygen ­ lowers pO2
Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads oxygen
Haemoglobin then returns to lungs to pick up more oxygen
Dissociation Curves Show How Affinity of Oxygen Varies
Shows how saturated Hb is with oxygen at any given partial pressure
100% saturation mean Hb is carrying all 4 oxygen molecules
0% saturation means none of Hb are carrying any O2

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Where pO2 is high Hb has high affinity for O2 (will readily combine with O2), so has high
saturation of O2
Where pO2 low (e.g. respiring tissues), haemoglobin has low affinity for O2, means it releases
O2, so low saturation of O2
Graph S-shaped because when Hb combines with first O2 molecule, shape alters in way which
makes it easier for other molecules to join too.…read more

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When CO2 levels increase, dissociation curve shifts down, showing that more O2 is released
from blood (because lower the saturation of haemoglobin with O2, more O2 is released)…read more


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