Respiratory: CO2 transport in the blood

Question 1

How much CO2 is in arterial blood compared to O2?

Why?

Answer 1

There is 2.5x more CO2 in arterial blood than O2
This is because CO2 has a major role in controlling blood pH, which is more important that transporting CO2 from the tissues to the lungs.

Question 2

What factor controls how much CO2 is dissolved in the plasma and what is the consequences?

Answer 2

Amount of dissolved CO2 depends of the partial pressure of CO2.
If pCO2 rises - plasma pH will fall
If pCO2 falls - plasma pH will rise

Question 3

How is HCO3- produced in RBCs?

Answer 3

CO2 and H2O readily diffuse into the RBC and react to form H+ and HCO3-.
The HCO3- leaves the RBC via the chloride bicarbonate exchanger.
Reaction sped up by carbonic anhydrase

Question 4

If there is more CO2 in venous blood why is the blood not more acidic?

Answer 4

There is more CO2 in venous blood and therefore more dissolved CO2 - much more is converted to HCO3- due to increased capacity of Hb for H+ (less oxygen). There is little change in plasma pH because both CO2 and HCO3-

Question 5

How does the body know to breath out the extra CO2 at the lungs and keep the correct amount in the plasma?

Answer 5

There is more O2 which is picked up by Hb therefore the H+ is given up. This H+ reacts with HCO3- to form CO2 which is breathed out