T4 - Gas exchange Flashcards
what is the relation between pressure and density for molecules in a gas system (air)?
they are proportional
what is atmopsheric pressure (Patm) and density of a gas at altitude?
less
what determines pressure of a gas in aqueous solution?
number of particles of gas and its solubility
what is the composition of air?
78% Nitrogen, 21% oxygen, other gases 1%
does fraction of oxygen in air change at altitude?
no, never
what is the fraction of inspired oxygen (FIO2)?
0.21
what is PIO2?
pressure of oxygen in inspired air
what equation denotes PIO2?
PIO2 = FIO2 x Patm
what is Patm at sea level?
101Kpa
what happens to the pressure of oxygen in the airways?
it drops
why does pressure of oxygen drop in the upper airways?
air is humidified which involves adding water vapour and this dilutes the amount of oxygen present therefore decreasing the pressure
what happens to the total pressure of air and the partial pressure of oxygen in the upper airways
total pressure or air stays the same but partial pressure of oxygen decreases due to water vapour
what can cold air in the upper airways cause?
bronchospasm
how does air move in the terminal airways?
by diffusion
what are the two main reasons that oxygen crosses the plasma membrane of the alveoli?
1) oxygen likes lipid and the plasma membranes of the alveoli are lipid rich
2) Palv is higher than Pblood for oxygen so diffuses along its conc grad
how long does it take for blood to equilibrate between the alveolus and blood?
0.33 seconds
how long does each blood particle spend in the alveolus?
one second
what is PAO2?
pressure of oxygen in the alveolus (PO2 in - PO2 out)
what is respiratory quotient (R)?
how much CO2 is produced for the amount of O2 that comes in
what happens to the pressure of oxygen when it moves from the alveolus to the blood and why?
it drops slightly as some small veins (thespian and bronchial) dump a little deoxygenated blood into the arterial circulation which dilutes it
what is anatomical shunting?
when blood doesn’t bypass the lungs to pick up oxygen - it goes directly from veins to arteries
what is venous admixture?
a small amount of venous blood mixing with the highly oxygenated arterial blood which accounts for the small drop in PAO2 to PaO2
how does oxygen get from the blood to the muscle?
jumps through endothelial wall of blood vessel then diffuses through the interstitial fluid to the muscle
what are the PO2 levels in the cell and what does this cause?
PO2 levels in the cell are low which causes oxygen to move into the cells
why are PO2 levels in the cell low?
due to mitochondrial activity which consume oxygen
what happens to the pressure of oxygen as it moves from inhaled air to mitochondria?
pressure drops which helps drive oxygen delivery
what two ways can oxygen be found in the blood?
1) dissolved (2%)
2) bound to Hb (98%)
approx how much oxygen is there per litre of blood?
200ml
what three things determine content of oxygen in the blood?
pressure of oxygen dissolved, solubility constant, amount bound to Hb
how much oxygen is delivered and consumed per minute?
1000ml delivered and 250ml consumed
how can oxygen delivery to tissues be increased?
increasing CO
how does CO binding to Hb affect oxygen?
impairs loading and unloading of oxygen on Hb (outcompetes it)
what will PaO2 and O2 sats be in CO poisoning?
normal
what are the symptoms of CO poisoning?
headache, nausea, vomiting, dizziness, lethargy, weakness, confusion and can lead to coma and death
what is methaemoglobinaemia?
when less oxygen is taken onto Hb as iron is oxidised from ferrous (Fe2+) to ferric (Fe3+)
what will PAO2 and PaO2 be in methaemoglobinaemia?
normal - pressure in alveoli and blood is normal but it can’t be loaded onto Hb
what happens to oxygen delivery in methaemoglobinaemia?
it decreases as it cant be loaded onto Hb
what three ways is CO2 transported in the blood?
bicarbonate (90%), dissolved (5%) and carbamino compounds (mostly Hb) 5%
what happens when CO2 binds the amine group on Hb and what situation is this useful in?
it ejects bound oxygen - useful for gas exchange
does oxygen or CO2 have a higher solubility and diffusion constant across the membrane?
CO2
does CO2 or oxygen equilibrate quicker across the membrane?
CO2
How much CO2 is in the alveolus and what does this allow?
not very much so CO2 can move down its pressure gradient from the blood to the alv to be expired
what can CO2 be measured from and what is this?
end tidal volume - big breath out then capture the last bit (same as CO2 alveolar pressure)
