Session 4: Carbon Dioxide In The Blood Flashcards
How much CO2 is there in arterial blood compared to O2?
Almost 2.5x as much
What is the total CO2 content of arterial blood?
21mmol/L
What is the total O2 content of arterial blood?
8.9mmol/L
What is the solubility factor for CO2 at normal body temperature?
0.23
What does dissolved CO2 form when it reacts with water?
Carbonic acid
What does carbonic acid dissociate into?
H+ and HCO3-
What is normal plasma concentration of HCO3-?
25mmol/L
What is the normal average concentration of dissolved CO2?
1.2mmol/L
How does increase in dissolved CO2 affect the position of equilibrium?
Pushes it to the right (increases production of HCO3-)
What two factors does the pH of plasma depend on?
Concentration of dissolved CO2
Conc. of HCO3-
What happens to plasma pH if pCO2 rises?
Falls (more acidic)
What happens to plasma pH if pCO2 falls?
Rises (more alkaline)
How is pCO2 of alveoli controlled?
By controlling the rate of ventilation
Which cation is mostly associated with HCO3-?
Na+
Why is pH of plasma alkaline?
High HCO3- concentration preventing dissolved CO2 from reacting
What is pK at normal body temp?
6.1
How much HCO3- is dissolved compared to CO2?
20x
Give the equation to calculate pH
pH = pK + log([HCO3-]/(pCO2 x 0.23))
What does carbonic anhydrase do?
Speeds up the reaction between CO2 and H2O
Why is production of HCO3- favoured in RBCs?
The RBCs will mop up the H+ ions and extrude the HCO3-
What transporter is used to extrude HCO3- from RBCs?
Chloride-bicarbonate exchanger
What does the ‘mopping up’ of H+ in the RBCs?
Negatively charged Hb
What is plasma HCO3- mostly determined by?
Binding of H+ to Hb
How are the kidneys involved in control of HCO3-?
They vary its excretion
How does HCO3- act as a buffer?
Reacts with acids produced to produce CO2
Why does the buffering action of HCO3- not affect pH greatly?
CO2 produced is removed by breathing
Where is pCO2 higher, in venous or arterial blood?
Venous
In which state of Hb do more H+ ions bind?
T state
In high pO2 will more or less H+ ions bind?
R state
Why is CO2 higher in the venous system?
It’s coming from metabolically active tissues
Why does more HCO3- form in venous blood?
Hb has been deoxygenated so will bind more H+
Why when dissolved CO2 increases in blood is there little change to pH?
More is converted to HCO3- as Hb binds more H+ (both HCO3- and pCO2 increase)
Why are carboamino compounds formed more at the tissues?
PCO2 is higher and unloading of O2 facilitates CO2 binding to Hb
Where on Hb does CO2 bind?
Directly to the amine groups of the globin of Hb
What three forms can CO2 be transported in?
Dissolved CO2
HCO3-
Carboamino compounds
What is the total CO2 content in whole venous blood?
23.3mmol/L
What percentage of total CO2 is transported?
8%
What is the majority of CO2 doing in the plasma?
Acting to buffer the pH
How much CO2 is transported at rest?
1.8mmol/L
What form does CO2 mostly travel in?
HCO3-
Is CO2 more commonly transported as carboamino compounds of dissolved CO2?
Carboamino compounds
