2. transporting CO2

CO2 TRANSPORT- 1 AND 2

• CO2 transported through circulatory system in 3 ways:

  • dissolved in plasma (5%)

  • associated w/ Hb to form carminohaemoglobin (10%)

CO2 TRANSPORT- 3 DIAGRAM

• 85% of CO2 is transported as hydrogen carbonate ions in erythrocytes

• enzyme carbonic anhydrase catalyses reversible reaction between CO2 and H2O

CO2 TRANSPORT- 3

• CO2 dissolves in H2O to form carbonic acid (carbonic anhydrase catalyst)

  • CO2 + H2O —> H2CO3

• carbonic acid releases H+ protons (acid dissociation)

  • H2CO3 —> HCO3^- + H+

• HCO3^- (hydrogencarbonate) ions diffuse out of erythrocyte

• Cl- diffuse into cell to balance charge —> CHLORIDE SHIFT

• H+ ions will bind w/ Hb to form haemoglobinic acid

CO2 EFFECT ON O2 DISSOCIATION

• O2 dissociates from oxyhaemoglobin where pO2 is low (i.e. respiring tissues)

• if H+ ions can bind w/ Hb, they must compete w/ O2

• in respiring tissue:

  • more CO2 produced

  • more carbonic acid formed

  • more H+ dissociated

  • more competition for Hb

  • more O2 dissociation

  • O2 released more readily to muscle cells

BOHR EFFECT

• in CO2 rich env (i.e. at respiring tissue) more O2 dissociates from oxyhaemoglobin

• O2 dissociation curve shifts right

• (requires higher pO2 to saturate Hb due to H+ competition)

• known as bohr effect