West's 9th ed - Chapter 6 - CO2 carriage (1)

Question 1

What are the three forms of CO₂ as it can be carried in the blood?

Answer 1

1) Dissolved
2) As bicarbonate
3) In combination with proteins as carbamino compounds

Question 2

Does CO₂ obey Henry’s law?

Answer 2

Yes. The amount of CO₂ dissolved is proportional to its partial pressure.

Question 3

How does the solubility of CO₂ compare to that of O₂?

Answer 3

CO₂ is 20 times more soluble.

Question 4

In arterial blood, what proportion of the CO₂ is in the form of bicarbonate?

Answer 4

90%

Question 5

Which reaction is catalyzed by carbonic anhydrase?

Answer 5

The conversion of H₂CO₃ to CO₂ + H₂O, or the reverse reaction.

Question 6

Where is carbonic anhydrase found?

Answer 6

In the RBCs

Question 7

How does this reaction occur:

H₂CO₃ → H⁺ + HCO₃^-

Answer 7

It happens quickly and spontaneously, without the aid of an enzyme

Question 8

What is the chloride shift?

Answer 8

This occurs in RBCs when the CO₂ becomes stored as bicarbonate. The reaction produces HCO₃^- (which diffuses out into the plasma) and H⁺. The RBC membrane is relatively impermeable to H⁺, and so Cl^- ions move into the RBC to maintain electrical neutrality.

Question 9

What is meant by “reduced Hb”?

Answer 9

This is the form of Hb after it has given away its O₂ in the peripheral tissues. Deoxyhaemoglobin.

Question 10

What is meant by the Haldane effect?

Answer 10

This refers to the fact that deoxygenation of the blood (as in the peripheral tissues) increases its ability to carry CO₂. Reduced Hb has a greater facility than HbO₂ to mop up H⁺ ions.

H⁺ + HbO₂ ⇔ H⁺.Hb + O₂

(for CO₂ stored as bicarbonate, forming H⁺ as a byproduct, which is easily taken up by displacing O₂ from Hb)

Also, reduced Hb can bind more CO₂ as carbaminohaemoglobin than can HbO₂

Question 11

What is the CO₂ concentration of arterial and mixed venous blood in mL/dL ? (mL/100mL)

How does this compare to O₂ concentration?

Answer 11

CO₂ concentration: Arterial 48mL/dL, Mixed Venous 53mL/dL.

O₂ concentration: Arterial 20mL/dL, Mixed Venous 15mL/dL.

Question 12

If plotted on the same scale, how does the CO₂-dissociation curve compare to the shape of the O₂-dissociation curve?

Answer 12

The CO₂ curve is steeper and more linear, with greater values on the y-axis (mL/dL)

Question 13

What shifts the CO₂-dissociation curve to the left? What shifts it to the right?

Answer 13

Increased O₂ saturation of Hb will shift the CO₂-dissociation curve to the right. Reduced SpO₂ shifts it to the left.