7 Carbon Dioxide in Blood

Question 1

In plasma, CO₂ may facilitate the formation of hydrogen ions and hydrogen carbonate ions. Why is this reaction slow?

Answer 1

Little carbonic anhydrase in plasma

Question 2

What is the dissolved concentration of CO₂ in plasma at a pCO₂ ​of 5.3kPa?

Answer 2

1.2mmol/L

Question 3

How is the hydrogen carbonate which is present in blood plasma formed?

Answer 3

In Red blood cells

reaction with CO₂

Requires carbonic anhydrase

Question 4

What happens to the pH if:

pCO₂ rises

[HCO₃^-] rises

Answer 4

Question 5

Write out the Henderson- Hasselbach equation.

Answer 5

Question 6

Why is it important that In plasma the ratio of [HCO₃^-] to dissolved CO₂ stays consistent?

Answer 6

[HCO₃^-] : CO₂

20:1

As long as this ratio stays consistent, pH will be 7.4

Question 7

What happens to the hydrogen ions which are formed from the reaction of CO₂ with H₂O in the presence of carbonic anhydrase? What does this cause?

Answer 7

Hydrogen ions bind to haemoglobin

Result: reaction drawn towards production of HCO₃^-

^{(Amount of CO₂ produced largely depends on buffering capacity of haemoglobin, only minor effect due to change in pCO₂)}

Question 8

How is the HCO₃^- exported from the red cell?

Answer 8

Exported in exchange for Cl^-

Chloride bicarbonate exchanger

Question 9

Name an organ in the body which has control over [HCO₃^-].

Answer 9

Kidney

Question 10

List all the forms in which carbon dioxide is carried in the blood:

Answer 10

(Carbamino compounds- formed by reaction of carbon dioxide with protein part of haemoglobin)

Question 11

Why is haemoglobin a ‘better buffer’ in venous blood?

Answer 11

Haemoglobin less saturated with oxygen

Question 12

What % of CO₂ is transported in the blood in the form of:

• Dissolved CO₂
• Hydrogen carbonate
• Carbaamino compounds

Answer 12

Question 13

Why is it that hyperventilation reduces the CO₂ content in the blood but has little effect on the oxygen concentration?

Answer 13

Relationship with pCO₂ and CO₂ is not sigmoidal. = almost linear (see graphs)

Question 14

How much carbon dioxide is taken from tissues and given off (ie transported)? What function does the rest of the carbon dioxide in the blood serve?

Answer 14

8% transported

Other CO₂ acts as buffering system