CO2 in Blood

Question 1

In what three forms is CO2 found in the body?

Answer 1

Dissolved in plasma (10%)
After reacting with water to form bicarbonate (60%)
Carbamino compounds (30%)

Question 2

Why is CO2 found in such high amounts in arterial blood?

Answer 2

It is important in buffering changes in pH of the blood

Question 3

What is a buffer?

Answer 3

Compounds able to bind or release hydrogen ions such that they dampen swings in pH

Question 4

What is the equation for the bicarbonate buffer system?

Answer 4

CO2 + H20 H2CO3 H+ + HCO3-

fully reversible reaction

Question 5

In which direction is the bicarbonate buffer system working in a healthy body?

Answer 5

Slight net favour of CO2 and H2O as products

Question 6

What controls the total concentration of bicarbonate ions in the body?

Answer 6

The kidney through selective reabsorption. Takes 3-5 days to compensate for changes

Question 7

Where is bicarbonate produced?

Why is this?

Answer 7

Red blood cells.

RBCs carry the enzyme carbonic anhydrase which catalyses breakdown of carbonic acid into constituent ions.

Question 8

How do red blood cells help buffer pH changes in blood?

Answer 8

Produce bicarbonate and excrete it via chloride bicarbonate exchanger.
Bind produced hydrogen ions to haemaglobin so they do not have an effect on pH.

Question 9

What governs the amount of hydrogen ions that can bind to haemoglobin?

Answer 9

The state of the molecule (and by extension oxygen status).
T state promotes H+ binding
R state makes binding more difficult

Question 10

Why can more bicarbonate ions be produced in venous blood?

Answer 10

1. Less O2 so Hb in T state
2. More H+ binds to haemoglobin
3. Decrease in H+ concentration drives buffer equation to favour production of H+ and HCO3-
4. HCO3- transported out of RBCs and into venous blood

Question 11

What happens to hydrogen ions when venous blood arrives at the lungs?

Answer 11

1. Hb picks up O2 and goes into R state
2. In R state, Hb gives up extra H+ ions
3. H+ reacts with HCO3- to form CO2
4. CO2 is breathed out

Question 12

What is the Haldane effect?

Answer 12

CO2 forming carbamino compounds dissociates from Hb when it enters its oxygen rich state

Question 13

How much CO2 is eliminated from the body at rest by the lungs?

Answer 13

8-10%

Question 14

How would you interpret acid base balance in ABG?

Answer 14

1.look at pH:
If >7.45 alkalosis
If <7.35 acidosis
2. Check pCO2
3. Look at HCO3-
4. Check for compensation