4. Carbon Dioxide In The Blood

Question 1

What are the 3 forms of CO2 in the blood?

Answer 1

Dissolved (10%)
HCO3- (60%)
Carbamino-haemoglobin compound (30%)

Question 2

What is the role of CO2 in blood?

Answer 2

Controlling blood pH

Question 3

What are buffers?

Answer 3

Compounds which are able to bind or release hydrogen ions such that they dampens swings in the pH

Question 4

What are the reactions in the bicarbonate buffer system?

Answer 4

CO2 + H2O H2CO3 H+ + HCO3-

Question 5

How do you work out CO2 dissolved in blood?

Answer 5

Solubility x pCO2

Question 6

What is plasma pH dependent on?

Answer 6

How much dissolved [CO2] reacts with water to form bicarbonate ions
Therefore depends on how much CO2 is present and how much HCO3- is present

Question 7

What happens to the plasma pH if pCO2 rises?

Answer 7

Plasma pH will fall

Question 8

What happens to the plasma pH if the pCO2 falls?

Answer 8

Plasma pH will rise

Question 9

What determines the arterial pCO2?

Answer 9

pCO2 of alveoli

Question 10

How and where is bicarbonate produced?

Answer 10

In red blood cells
CO2 + H2O HCO3- + H+
HCO3- then moves out of RBC into blood and Cl- ions move in
H+ binds to haemoglobin

Question 11

What is the reaction producing bicarbonate ions sped up by?

Answer 11

Carbonic anhydrase

Question 12

What is HCO3- conc controlled by?

Answer 12

Kidney

Question 13

What happens when there are higher levels of acid in the body?

Answer 13

Acids react with HCO3- to produce CO2
CO2 levels increase
Extra CO2 produced is removed by breathing and pH changes are minimised (buffered)
More HCO3 needs to be produced

Question 14

What does buffering of H+ by Hb depend on?

Answer 14

Levels of oxygenation
If more O2 binds Hb - R state, fewer H+ ions bind
If less O2 binds Hb - T state, more H+ ions bind

Question 15

What happens when venous blood arrives at the lungs?

Answer 15

Hb picks up O2 and goes into R state
Hb then gives up extra H+ it took on at tissues
H+ reacts with HCO3- to form CO2
Reaction pushed to left
CO2 breathed out

Question 16

What happens in the formation of carbamino compounds?

Answer 16

Binds directly to amine groups of globin on Hb

Question 17

Where are more carbamino compounds formed?

Answer 17

At the tissues
Because pCO2 higher, and unloading of O2 from Hb facilitates binding of CO2 to Hb
Oxygen poor Hb (T state) binds CO2 better

Question 18

What is the Haldane effect?

Answer 18

CO2 is given up at lungs as the Hb becomes oxygen rich, oxygenated Hb unloading CO2

Question 19

How much CO2 is transported to the lungs to be eliminated?

Answer 19

~8% at rest