Gas transport - carbon dioxide Flashcards
Which 3 ways is CO2 transported in the blood? Provide percentages.
As dissolved CO2 – 10%
As bicarbonate (HCO3-) – 69%
As carbamino compounds – 21%
Carbon dioxide reacts with water to form what?
Carbonic acid – H2CO3
Carbonic acid dissociates to form what?
H+ and HCO3-
What is the definition of an acid?
Any chemical that can donate H+ (proton)
What is the definition of a base?
Any chemical that can accept H+
What is the definition of a strong acid?
An acid which completely dissociates in solution
E.g. Hydrochloric acid becomes H+ and Cl-
A weak acid with its conjugate base forms what?
A buffer pair
What is the average pH of blood?
7.4
Acidity in the body can come from which 2 types of acids?
Volatile acids
Non-volatile acids
What are volatile acids?
Acids that can easily be converted to gases
What are volatile acids excreted by?
Lungs
What are non-volatile acids excreted by?
Kidneys
The Henderson-Hasselbalch is used to calculate what?
What 2 things are used to calculate it?
pH
Bicarbonate + CO2
Describe how pH would be restored if too much H+ was produced.
H+ reacts with bicarbonate ions to form CO2. CO2 is breathed out, restoring pH
Describe how pH would be restored if concentration of CO2 was too high.
Kidneys excrete less HCO3-, raising HCO3- plasma and restoring pH
The reaction between CO2 and H2O is catalysed by which enzyme?
Carbonic anhydrase
Where is carbonic anhydrase present and not present?
Present - red blood cells
Not present - blood plasma
When CO2 reacts with H2O in red blood cells, how are the products (H+ and HCO3-) removed?
H+ is buffered by haemoglobin
HCO3- is transferred to plasma
The buffering ability of haemoglobin with H+ ions is enhanced by what mechanism?
Deoxygenation
What is the Haldane effect?
Giving up O2 increases the uptake of CO2 by haemoglobin
What is the partial pressure value of oxygen in arterial blood?
13.3 kPa
What is the partial pressure value of CO2 in arterial blood?
5.3 kPa
What is the partial pressure value of oxygen in venous blood?
6 kPa
What is the partial pressure value of CO2 in venous blood?
6.5 kPa
What is the definition of a weak acid?
An acid which only partially dissociates in solution
E.g. H2CO3 becomes H+ and HCO3
Why does the reaction between CO2 and H2O occur more rapidly in red blood cells compared to plasma?
Carbonic anhydrase is not present in plasma, but it is present in red blood cells
How does HCO3- leave red blood cells?
Cl- HCO3 - exchanger (antiporter)
What is the main carbamino compound?
Carbamino haemoglobin
Which part of haemoglobin does CO2 bind with to form carbamino haemoglobin?
NH2 group
