Movement of CO2 between Tissues and Blood (PK7)

Question 1

How does CO2 initially leave metabolising cells?

Answer 1

• Produced in dissolved form
• Due to partial pressure gradients, moves into plasma

Question 2

Where does CO2 go from the plasma?

Answer 2

• Some retained dissolved in plasma
• Some moves down pressure gradient into RBCs
• Some reacts with water uncatalysed (CO2 + H2O –> H2CO3 –> HCO3- + H+)
• Some reacts to form carbamino compounds (CO2 + R-NH2 –> R-NHCOO- + H+)

Question 3

What happens to CO2 entering RBCs?

Answer 3

• Some retained dissolved
• Some oxygenates deoxy Hb –> oxy Hb
• Some reacts with water (step 1 catalysed by carbonic anhydrase) (CO2 + H2O –> H2CO3 –> HCO3- + H+)

Question 4

Where is most of the bicarbonate produced from CO2 found and why?

Answer 4

• Plasma
• Increased concentrations in RBCs mean it diffuses into plasma
• Electrical gradient counteracted by movement of Cl- ions into RBCs from plasma

Question 5

What counteracts fall in pH in the plasma?

Answer 5

• CO2 reacts to form carbamino compounds
• These are negative so buffer H+

Question 6

What buffers H+ in RBCs?

Answer 6

Carbamino compounds formed in RBCs binds to deoxy Hb

Question 7

What does buffering of H+ in RBCs prevent?

Answer 7

• Equilibrium being reached
• Pulls reaction to the right –> CO2 continuously moved out of tissues