Is oxygen soluble in water?
How much dissolved oxygen does plasma contain at a partial pressure of 13.3kPa and a temperature of 37oC?
How much oxygen do we need at rest?
12mmol per minute
What volume of plasma would be required to meet the bodys oxygen requirements if the only source was dissolved oxygen?
What is the typical ppO2 in the lungs?
What is the typical ppO2 in the tissues?
Draw an oxygen haemoglobin dissociation curve
What does haemoglobin do?
With respect to oxygen binding
Reversibly binds to oxygen over a very narrow range of ppO2
Describe the structure of haemoglobin
Tetrameric protein, made up of 2 α and 2 ß subunits, with 4 haem groups
What is the result of haemoglobin having 4 Haem groups?
It can bind to four molecules of oxygen
What factors can decrease the affinity of Hb for O2?
- Increasing temperature
- Increased CO2
What happens at sites of low pH and increased CO2?
More oxygen is required and will be released
What tissue may experience low pH and increased CO2?
Muscle tissue during exercise
What is the effect of low pH and increased CO2 on haemoglobin dissociation called?
The Bohr effect
What happens to the oxygen dissociation curve as a result of the Bohr effect?
It shifts to the right
Draw a graph illustrating the effect of changing conditions on the oxygen dissociation curve
What happens if the pO2 in the capillaries falls?
pH falls and temperature falls, so Hb will give up more oxygen
What is the result of a pO2 fall in the capillaries on the saturation of Hb leaving the capillaries?
It is greatly reduced
What can be used to calculated the percentage of oxygen that has been given up in a tissue if venous pO2 is known?
A dissociation curve
What happens to blood flowing through alveolar capillaries?
It picks up oxygen and looses carbon dioxide by diffusion of those gases across the alveolar wall
What is the rate at which gases exchange determined by?
- Area available for exchange
- Resistance to diffusion
- Gradient of partial pressure
What can be used to calculate the transfer factor of the lungs?
What reactions can carbon dioxide undertake in the blood?
- Dissolves in water
- Reacts in water
- Binds directly to proteins
How does the solubility of carbon dioxide compare to that of oxygen?
It is more soluble
What does carbon dioxide form when it reacts with water?
H+ and HCO3-
Is the reaction of carbon dioxide and water reversible?
Yes, depending on the concentration of reactants
What is formed when carbon dioxide binds directly to proteins in the blood?
What is the Henderson-Hasselbach equation?
pH = 6.1 + Log( [HCO3-] / (pCO2 x 0.23) )
What happens to carbon dioxide in plasma?
It dissolves in plasma and undergoes a slow reaction with water, creating HCO3-
Why does carbon dioxide undergo a slow reaction with water in plasma?
Because there is little carbonic anhydrase
What happens to carbon dioxide in RBCs?
It reacts with water rapidly to form H+ and HCO3-
Why does carbon dioxide react with water rapidly in RBCs?
Because carbonic anhydrase is present
What happens to the H+ ions formed in carbon dioxides reaction with water in RBCs?
They bind to Hb
What is the result of H+ ions binding to Hb?
It draws the reaction towards HCO3-
What does the amount of HCO3- produced by carbon dioxide reacting with water in RBCs depend on?
Primarily, the buffering effects of Hb
Why can Hb be said to act as a buffer?
H+ ions bind to Hb, so it acts as a buffer by 'mopping up' the ions
What does the buffering action of Hb drive?
The reaction of carbon dioxide and water, and therefore the production of H+ and HCO3-
What do carbamino compounds do?
Bind directly to proteins
What does the binding of carbamino compounds to proteins contribute to?
Carbon dioxide transport
NOT acid base balance
Are more carbamino compounds formed in arterial or venous blood?
Slightly more in venous blood
Why are there slightly more carbamino compounds formed in venous blood?
Because pCO2 is higher
What is the normal carbon dioxide content of arterial blood?
What is the normal carbon dioxide content of venous blood?
How much carbon dioxide is transported from the tissues to the lungs?
How is the amount of carbon dioxide transported from the tissues to the lungs calculated?
Venous blood carbon dioxide - Arterial blood carbon dioxide
In what forms does carbon dioxide travel from the tissues to the lungs?
- 80% travels as HCO3-
- 11% travels as carbamino compounds
- 8% travels as dissolved CO2
What does the amount of CO2 that travels from the tissues to the lungs as HCO3- depend on?
How much O2 has been lost, allowing it to bind to H+