transport of oxygen and carbon dioxide in the blood

• Explain how oxygen is transported to respiring tissue (formation of carbonic acid within a RBC)

  • CO2 + H2O <=> H2CO3
  • H2CO3 <=> H+ + HCO3- (carbonic acid dissociates to form hydrogencarbonate ion- moves out of plasma and Cl- diffuses in to balance charges out- maintains electrical balance) (chloride shift)
  • HbO2 + H+ <=> O2 + HHb (oxygen diffuses out to respiring cells)
• What compound forms when oxygen binds to haemoglobin?

  Oxyhaemoglobin
• What three different ways is carbon dioxide transported from the tissues to the lungs?

  • 5% dissolved in plasma
  • 10-20% combined with haemoglobin to form carbaminohaemoglobin
  • 75-85% converted into hydrogen carbonate ions in the cytoplasm of the RBCs
• What is the role of harmoglobin in controlling pH within a erythrocyte?

  • Removes free hydrogen ions from erythrocytes
  • Binds to them to form haemoglobinic acid
  • In this way it acts as a buffer and prevents changes in pH
• state why the biconcave shape of erythrocytes is a useful adaptation

  • larger surface area for diffusion of gases
  • helps them to pass through narrow capillaries
• state the process of how oxygen binds to erythrocytes in the lungs

  1. erythrocytes enter the lung capillaries, where the oxygen concentration is higher than in erythrocytes
  2. creates steep conc grad between inside of erythrocytes and the air of the alveoli
  3. oxygen moves into erythrocytes and binds to haemoglobin
  4. haemoglobin changes shape, making it easier for the next oxygen molecules to bind. This is known as positive co-operaitivity
  5. because the oxygen is bound to the haemoglobin, the free oxygen conc in the RBC remains low, so a steep conc grad is maintained until the erythrocyte is completely saturated with O2
• state how oxygen is released from erythrocytes when they come into contact with body cells

  1. concentration of oxygen in the cytoplasm of body cells is lower than of erythrocytes
  2. sets up a concentration/diffusion gradient
  3. oxygen diffuses out of erythrocyte down a conc grad
  4. once the first O2 molecule is released by haemoglobin, the molecule changes shape and it becomes easier to remove the rest of the oxygen molecules
• state the changes that take place in % saturation of haemoglobin in varying partial pressures of O2

  changes:

  A) easier

  B) more

  C) saturated

  D) partial pressure

  E) small

  F) rapidly

  
• What is the Bohr effect and why is it important?

  • haemoglobin gives up oxygen more readily at high partial pressures of CO2
  • When there’s a high partial pressure of CO2, haemoglobin gives up oxygen more readily
  • At low proportions of CO2, oxygen binds to haemoglobin molecules more easily

  
• explain how a foetus is able to be supplied with enough oxygen during pregnancy (PPQ 2023)

  • at the same partial pressures of oxygen, foetal haemoglobin has higher affinity for oxygen than the mother
  • when there are low partial pressures of oxygen in placenta, oxygen dissociates from adult haemoglobin in placenta and diffuses from maternal to foetal blood
  • there is an increased saturation of foetal haemoglobin with oxygen at lower partial pressures of oxygen
• what enzyme catalyses the reaction between carbon dioxide and water in RBCs to form carbonic acid?

  carbonic anhydrase