17 carriage of CO2 Flashcards
What are the waste products of metabolism per minute?
0.16g H20
1.22 kcal heat
200ml CO2
What are the 3 ways that CO2 are carried in the blood?
dissolved as CO2 (has a partial pressure)
bound to proteins as carboamino compounds
as bicarbonate ions
How much CO2 is dissolved in arterial and venous blood?
What Law dictates this?
arterial - 5kPa
venous - 6kPa
5% of total Co2 is dissolved
In Red Blood Cells, what is CO2 bound to?
alpha and beta globin chains
deoxy Hb binds more to CO2 than OxyHb (the haldane effect)
What proportion of CO2 is transported as bicarbonate ions?
90%
What equilibrium is associated with CO2 and HCO3?
CO2 + H20 H2CO3 HCO3- + H+
What is the driving force pulling CO2 out of the mitochondria (the thing pulling the reaction ‘right’)
buffered H+ in RBC’s
What are the 3 main differences between the PO2 and PCO2 dissociation curves?
amount of gas in each body
shape of curves (sigmoid PO2 vs linear PCO2)
Haldane vs Bohr effect
What is the significance of the haldane and bohr effects?
physiological importance for blood gas carriage in the lungs and peripheral tissues
Which 2 factors account for the Haldane effect?
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)
What is the ‘normal’ pH range?
0.15 pH units around 7.4
this is still quite a big change in [H+]
What is the reasoning behind the henderson - Hasselbach equation?
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
What are the 3 features of the CO2 / HCO3- buffer system making it the most relevant system in the blood?
high concentrations are easy to measure
metabolism adds CO2 to the blood
both components can be regulated (by the kidney and the lungs)
In the HH equation, if the denominator should be [HA], why do we have PCO2 there and not H2CO3?
H2CO3 exists in small concentrations (hard to measure)
easier to replace with PCO2, multiplied by a constant
In the HH equation, why is the solubility constant 0.23, and not 5.2?
because the UNITS here are different
0.23 mmol L-1 kPa-1
NOT 5.2 ml L-1 kPa-1
What is the pK(1)?
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
how many HCO3 molecules are there per CO2?
What is the signifiance of this in terms of pH?
20
pH = 6.1 + log20
the pH with always be 7.4 if the ration of [HCO3-] / [PCO2 x 0.23] remains 20
What possible causes of pH disturbance stem from a respiratory problem causing PCO2 to be altered?
respiratory acidosis / alkalosis
otherwise metabolic acidosis / alkalosis
compensation occurs via the unaffected system (lungs or kidneys)
why do we have respiratory acidosis?
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
Where is the highest amount of CO2?
respiring systemic tissues, as it has to travel down its’concentration gradient
What happens to the venous - alveolar difference of dissolved PCO2 in exercise?
it increases
Why is the haldane effect important in the lungs?
there isn’t much of a Bohr effect in the lungs
What is the Haldane effect?
the reduced affinity for CO2 in the lungs, allowing O2 to displace it
What is the core difference between the Bohr and Haldane effect?
the Bohr effect gets CO2 to bind to haem, the Haldane effect gets it to dissociate
