CO2 In Blood

Question 1

In what 3 forms does CO2 exist in the blood?

Answer 1

• Dissolved in plasma
• Reacts with water to form HCO3-
• Reacts with Hb to form Carbamino-Haemoglobin

Question 2

What is a buffer?

Answer 2

Compounds which are able to bind/ release hydrogen ions, in order to minimise pH changes

Question 3

In the Plasma, dissolved CO2 slowly turns into H+ and HCO3-.

Why is this slow?

Answer 3

Little Carbonic Anhydrase needed to form Carbonic Acid, which rapidly dissociates into H+ and HCO3-

Question 4

What is the ratio of [HCO3-] to Dissolved CO2 in plasma?

What determines the pH?

Answer 4

20:1 (More HCO3-)

Ratio of HCO3- to dissolved CO2 (pCO2* Solubility coefficient)

Question 5

Where is Bicarbonate made?

How? What happens to H+?

Answer 5

• CO2 enters RBC and reacts with H2O, catalysed by Carbonic Anhydrase, forming Carbonic Acid
• Carbonic acid dissociates into HCO3- and H+
• HCO3- leaves RBC through Cl-HCO3 Antiport, whilst Cl enters RBC
• H+ binds to Hb-

Question 6

What is the significance of H+ binding to Hb in RBC?

Answer 6

Draws reaction towards HCO3- production, as H+ is being ‘removed’ from equation

Question 7

Does Hb’s buffering capacity affect [HCO3-] less or more than pCO2?

Answer 7

Hb’s buffering capacity as this ensures H+ is removed from equation, allowing HCO3- production to continue rapidly

Question 8

Although the RBCs make HCO3-, where is Plasma [HCO3-] controlled?

Answer 8

In the kidneys

Question 9

Considering Plasma and RBC HCO3- production, what 2 things determine pH?

Answer 9

• Amount of CO2 dissolved in plasma

- Amount of HCO3- formed from CO2 in RBC

Question 10

Briefly outline how does Bicarbonate buffer acid

Answer 10

• More H+ from acids reacts with HCO3-
• More carbonic acid made-> More CO2+H2O
• Hyperventilation to remove CO2 and more HCO3-must be made to replenish stores

Question 11

Describe how O2 binding affects H+ binding to Hb

Answer 11

• More O2 binds-> R state and less H+ binding

- Less O2 binds-> T state and more H+ binding

Question 12

How does reduced O2 levels affect HCO3- transport in blood?

In veins, at metabolic tissues

Answer 12

• Less O2: Hb-> T state and binds more H+

- In RBC, this allows more HCO3- to be made and moved out of cell into plasma

Question 13

How does increased O2 levels affect HCO3- and CO2 transport in blood?

(At lungs)

Answer 13

• More O2: Hb-> R state and gives up H+
• H+ reacts with HCO3- in plasma-> H2CO3-> CO2 + H20
• CO2 is breathed out

Question 14

List from Low to High the proportion of CO2 transported in blood as;

• Bicarbonate
• Carbamino compounds
• Dissolved CO2

Answer 14

1. Dissolved O2: 8%
2. Carbamino compounds: 12%
3. Bicarbonate: 80%

(Values may vary widely across literature, however magnitude remains same)

Question 15

At REST, How much CO2 transported in blood is to be eliminated?

How much is part of pH buffering system?

Answer 15

8% to be eliminated

92% to keep acid-base balance

Question 18

Give 2 reasons why more Carbamino-haemoglobin is formed at tissues

Answer 18

• Higher pCO2

- Unloading of O2 facilitates increased binding of CO2 to Hb

Question 19

What is the Haldane Effect?

Answer 19

This describes the phenomenon where;

• Low O2 levels promotes binding of CO2 to Hb
• High O2 levels promotes release of CO2 from Hb

Question 24

What 2 things determine the reaction of CO2 with Hb?

Does this reaction contribute to maintaining the acid-base balance?

Answer 24

• CO2 concentration
• Oxygenation state of Hb

No, but does contribute CO2 transport