Transport of carbon dioxide

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Transport of carbon dioxide
H
2
Transport of carbon dioxide

• CO2 is carried in three ways
• 5 carried in solution in the plasma as CO2
• 10 combines with the Hb in the form of
  carbamino-haemoglobin
• 85 is carried as hydrogen carbonate

H
3
Transport of carbon dioxide

• The way in which hydrogen carbonate is formed is
  important and needs to be known in detail.

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Transport of carbon dioxide

• In tissue

CO2
plasma
5
Transport of carbon dioxide

• In tissue

plasma

H2O
H

HCO3-
CO2
6
Transport of carbon dioxide

• In lungs

plasma
HCO3-
7
Transport of carbon dioxide

• In lungs

plasma
HCO3-
CO2

H2O
H

8
Transport of carbon dioxide

• In lungs

plasma
CO2

H2O
H

HCO3-
9
Formation of hydrogen carbonate

• CO2 diffuses from tissues into rbc
• Some combines with amino groups to form
  carbamino-haemoglobin
• The RBC contain an enzyme called carbonic
  anhydrase which catalyses the reaction between
  CO2 and water to form carbonic acid

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Formation of hydrogen carbonate

• Carbonic acid dissociates into negatively charged
  hydrogen carbonate and positive hydrogen ions
• The hydrogen ions increase the acidity of the
  blood
• The H combine with Hb to give haemoglobinic
  acid.
• This decreases the affinity of Hb to oxygen so it
  gives it up to the tissues (hence 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 inside
  of the RBC positively charged.
• In order to balance this electric charge chloride
  ions diffuse into the rbc from the plasma this
  is known as the chloride shift.
• In this reaction Hb is acting as a buffer

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Formation of hydrogen carbonate

• When blood gets to the lungs, all the reactions
  are reversed
• The hydrogen carbonate and hydrogen ions
  recombine releasing CO2
• The chloride shift is reversed
• Carbamino-haemoglobin breaks down to release CO2