4. Blood Gas Carriage Flashcards
What is the plasma content of dissolved oxygen at partial pressure 13.3kPa and at a temperature of 37C?
0.13mmol/L.
How much oxygen do we need per minute at rest?
12mmol.
How many litres of blood would be needed for the 12mmol demand at rest if oxygen was only dissolved in the blood?
92 litres.
What is the typical ppO2 in the lungs?
13.3kPa.
What is the typical ppO2 in the tissues?
5kPa.
What is the shape of an oxygen-haemoglobin dissociation curve?
Sigmoidal curve.
What is the structure of haemoglobin?
A tetrameric protein with 2 alpha and 2 beta subunits.
How many molecules of oxygen can haemoglobin bind to?
Four molecules.
What are the two states of haemoglobin?
Low affinity T state, and high affinity R state.
What happens to Hb state when O2 binds?
More R state which promotes more O2 binding.
What decreases affinity of Hb for O2?
H+, increasing temperature and CO2.
What is the Bohr effect?
Where there is low pH, in metabolically active tissue for example, more oxygen is required so the oxygen dissociation curve shifts right and O2 is more readily given off.
How can the amount of oxygen given to a tissue be calculated?
If venous pO2 is know, the dissociation curve can calculate it.
What affects the rate of gas exchange?
Area available for the exchange, resistance to diffusion, gradient of partial pressure.
How can transfer factor be calculated?
With carbon monoxide.
How does CO2 react in the blood?
It dissolves in water, or reacts with water, and binds directly to proteins.
How does solubility in water differ between CO2 and O2?
CO2 is more soluble in water than O2.
How does CO2 react with water in blood?
It forms H+ and HCO3-. This is a reversibly reaction.
What does CO2 form when it binds directly to proteins?
Carbamino compounds.
What is the Henderson-Hasselbach equation?
pH = 6.1 + log ([HCO3-]/(pCO2 x 0.23))
What is the slow reaction of CO2 in plasma?
With water to create HCO3-.
Why is the reaction of CO2 and water slow in the plasma?
Little carbonic anhydrase to catalyse it.
How does CO2 react with water in red blood cells?
Rapidly to form H+ and HCO3-.
What does the amount of HCO3- made by CO2 in RBCs depend on?
The buffering effects of Hb.
