4. Carbon Dioxide In The Blood Flashcards
What are the 3 forms of CO2 in the blood?
Dissolved (10%)
HCO3- (60%)
Carbamino-haemoglobin compound (30%)
What is the role of CO2 in blood?
Controlling blood pH
What are buffers?
Compounds which are able to bind or release hydrogen ions such that they dampens swings in the pH
What are the reactions in the bicarbonate buffer system?
CO2 + H2O H2CO3 H+ + HCO3-
How do you work out CO2 dissolved in blood?
Solubility x pCO2
What is plasma pH dependent on?
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
What happens to the plasma pH if pCO2 rises?
Plasma pH will fall
What happens to the plasma pH if the pCO2 falls?
Plasma pH will rise
What determines the arterial pCO2?
pCO2 of alveoli
How and where is bicarbonate produced?
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
What is the reaction producing bicarbonate ions sped up by?
Carbonic anhydrase
What is HCO3- conc controlled by?
Kidney
What happens when there are higher levels of acid in the body?
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
What does buffering of H+ by Hb depend on?
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
What happens when venous blood arrives at the lungs?
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
What happens in the formation of carbamino compounds?
Binds directly to amine groups of globin on Hb
Where are more carbamino compounds formed?
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
What is the Haldane effect?
CO2 is given up at lungs as the Hb becomes oxygen rich, oxygenated Hb unloading CO2
How much CO2 is transported to the lungs to be eliminated?
~8% at rest
