17 carriage of CO2

Question 1

What are the waste products of metabolism per minute?

Answer 1

0.16g H20
1.22 kcal heat
200ml CO2

Question 2

What are the 3 ways that CO2 are carried in the blood?

Answer 2

dissolved as CO2 (has a partial pressure)
bound to proteins as carboamino compounds
as bicarbonate ions

Question 3

How much CO2 is dissolved in arterial and venous blood?

What Law dictates this?

Answer 3

arterial - 5kPa
venous - 6kPa

5% of total Co2 is dissolved

Question 4

In Red Blood Cells, what is CO2 bound to?

Answer 4

alpha and beta globin chains

deoxy Hb binds more to CO2 than OxyHb (the haldane effect)

Question 5

What proportion of CO2 is transported as bicarbonate ions?

Answer 5

90%

Question 6

What equilibrium is associated with CO2 and HCO3?

Answer 6

CO2 + H20 H2CO3 HCO3- + H+

Question 7

What is the driving force pulling CO2 out of the mitochondria (the thing pulling the reaction ‘right’)

Answer 7

buffered H+ in RBC’s

Question 8

What are the 3 main differences between the PO2 and PCO2 dissociation curves?

Answer 8

amount of gas in each body
shape of curves (sigmoid PO2 vs linear PCO2)
Haldane vs Bohr effect

Question 9

What is the significance of the haldane and bohr effects?

Answer 9

physiological importance for blood gas carriage in the lungs and peripheral tissues

Question 10

Which 2 factors account for the Haldane effect?

Answer 10

Deoxy Hb is 3.5x more effective at binding to CO2 than oxy Hb

Deoxy Hb binds H+ more avidly than HbO2 (therefore, the equilibrium is pushed more to the right, so more CO2 is carried and thus more O2 is released)

Question 11

What is the ‘normal’ pH range?

Answer 11

0.15 pH units around 7.4

this is still quite a big change in [H+]

Question 12

What is the reasoning behind the henderson - Hasselbach equation?

Answer 12

the pH of a solution is dertmined by the pK of the buffer system in operation and the concentration of its’ ionised ([A-]) and unionised ([HA]) forms

therfore, for a given buffer system, the ratio of [A-] / [HA] defines a unique pH

Question 13

What are the 3 features of the CO2 / HCO3- buffer system making it the most relevant system in the blood?

Answer 13

high concentrations are easy to measure

metabolism adds CO2 to the blood

both components can be regulated (by the kidney and the lungs)

Question 14

In the HH equation, if the denominator should be [HA], why do we have PCO2 there and not H2CO3?

Answer 14

H2CO3 exists in small concentrations (hard to measure)

easier to replace with PCO2, multiplied by a constant

Question 15

In the HH equation, why is the solubility constant 0.23, and not 5.2?

Answer 15

because the UNITS here are different
0.23 mmol L-1 kPa-1
NOT 5.2 ml L-1 kPa-1

Question 16

What is the pK(1)?

Answer 16

the pK is the negative log of the dissociation constant BUT the units required to convert H2CO3 to PCO2 mean the pK(1) is the apparent pK of the system and has a value of 6.1

Question 17

how many HCO3 molecules are there per CO2?

What is the signifiance of this in terms of pH?

Answer 17

20

pH = 6.1 + log20
the pH with always be 7.4 if the ration of [HCO3-] / [PCO2 x 0.23] remains 20

Question 18

What possible causes of pH disturbance stem from a respiratory problem causing PCO2 to be altered?

Answer 18

respiratory acidosis / alkalosis

otherwise metabolic acidosis / alkalosis

compensation occurs via the unaffected system (lungs or kidneys)

Question 19

why do we have respiratory acidosis?

Answer 19

when we exercise we produce CO2 and H+ ions

we ventilate to regulate O2 and CO2 levels

if we have a problem with ventilation, the blood becomes more acidic

Question 20

Where is the highest amount of CO2?

Answer 20

respiring systemic tissues, as it has to travel down its’concentration gradient

Question 21

What happens to the venous - alveolar difference of dissolved PCO2 in exercise?

Answer 21

it increases

Question 22

Why is the haldane effect important in the lungs?

Answer 22

there isn’t much of a Bohr effect in the lungs

Question 23

What is the Haldane effect?

Answer 23

the reduced affinity for CO2 in the lungs, allowing O2 to displace it

Question 24

What is the core difference between the Bohr and Haldane effect?

Answer 24

the Bohr effect gets CO2 to bind to haem, the Haldane effect gets it to dissociate