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