T4 - Gas exchange

Question 1

what is the relation between pressure and density for molecules in a gas system (air)?

Answer 1

they are proportional

Question 2

what is atmopsheric pressure (Patm) and density of a gas at altitude?

Answer 2

less

Question 3

what determines pressure of a gas in aqueous solution?

Answer 3

number of particles of gas and its solubility

Question 4

what is the composition of air?

Answer 4

78% Nitrogen, 21% oxygen, other gases 1%

Question 5

does fraction of oxygen in air change at altitude?

Answer 5

no, never

Question 6

what is the fraction of inspired oxygen (FIO2)?

Answer 6

0.21

Question 7

what is PIO2?

Answer 7

pressure of oxygen in inspired air

Question 8

what equation denotes PIO2?

Answer 8

PIO2 = FIO2 x Patm

Question 9

what is Patm at sea level?

Answer 9

101Kpa

Question 10

what happens to the pressure of oxygen in the airways?

Answer 10

it drops

Question 11

why does pressure of oxygen drop in the upper airways?

Answer 11

air is humidified which involves adding water vapour and this dilutes the amount of oxygen present therefore decreasing the pressure

Question 12

what happens to the total pressure of air and the partial pressure of oxygen in the upper airways

Answer 12

total pressure or air stays the same but partial pressure of oxygen decreases due to water vapour

Question 13

what can cold air in the upper airways cause?

Answer 13

bronchospasm

Question 14

how does air move in the terminal airways?

Answer 14

by diffusion

Question 15

what are the two main reasons that oxygen crosses the plasma membrane of the alveoli?

Answer 15

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

Question 16

how long does it take for blood to equilibrate between the alveolus and blood?

Answer 16

0.33 seconds

Question 17

how long does each blood particle spend in the alveolus?

Answer 17

one second

Question 18

what is PAO2?

Answer 18

pressure of oxygen in the alveolus (PO2 in - PO2 out)

Question 19

what is respiratory quotient (R)?

Answer 19

how much CO2 is produced for the amount of O2 that comes in

Question 20

what happens to the pressure of oxygen when it moves from the alveolus to the blood and why?

Answer 20

it drops slightly as some small veins (thespian and bronchial) dump a little deoxygenated blood into the arterial circulation which dilutes it

Question 21

what is anatomical shunting?

Answer 21

when blood doesn’t bypass the lungs to pick up oxygen - it goes directly from veins to arteries

Question 22

what is venous admixture?

Answer 22

a small amount of venous blood mixing with the highly oxygenated arterial blood which accounts for the small drop in PAO2 to PaO2

Question 23

how does oxygen get from the blood to the muscle?

Answer 23

jumps through endothelial wall of blood vessel then diffuses through the interstitial fluid to the muscle

Question 24

what are the PO2 levels in the cell and what does this cause?

Answer 24

PO2 levels in the cell are low which causes oxygen to move into the cells

Question 25

why are PO2 levels in the cell low?

Answer 25

due to mitochondrial activity which consume oxygen

Question 26

what happens to the pressure of oxygen as it moves from inhaled air to mitochondria?

Answer 26

pressure drops which helps drive oxygen delivery

Question 27

what two ways can oxygen be found in the blood?

Answer 27

1) dissolved (2%)

2) bound to Hb (98%)

Question 28

approx how much oxygen is there per litre of blood?

Answer 28

200ml

Question 29

what three things determine content of oxygen in the blood?

Answer 29

pressure of oxygen dissolved, solubility constant, amount bound to Hb

Question 30

how much oxygen is delivered and consumed per minute?

Answer 30

1000ml delivered and 250ml consumed

Question 31

how can oxygen delivery to tissues be increased?

Answer 31

increasing CO

Question 32

how does CO binding to Hb affect oxygen?

Answer 32

impairs loading and unloading of oxygen on Hb (outcompetes it)

Question 33

what will PaO2 and O2 sats be in CO poisoning?

Answer 33

normal

Question 34

what are the symptoms of CO poisoning?

Answer 34

headache, nausea, vomiting, dizziness, lethargy, weakness, confusion and can lead to coma and death

Question 35

what is methaemoglobinaemia?

Answer 35

when less oxygen is taken onto Hb as iron is oxidised from ferrous (Fe2+) to ferric (Fe3+)

Question 36

what will PAO2 and PaO2 be in methaemoglobinaemia?

Answer 36

normal - pressure in alveoli and blood is normal but it can’t be loaded onto Hb

Question 37

what happens to oxygen delivery in methaemoglobinaemia?

Answer 37

it decreases as it cant be loaded onto Hb

Question 38

what three ways is CO2 transported in the blood?

Answer 38

bicarbonate (90%), dissolved (5%) and carbamino compounds (mostly Hb) 5%

Question 39

what happens when CO2 binds the amine group on Hb and what situation is this useful in?

Answer 39

it ejects bound oxygen - useful for gas exchange

Question 40

does oxygen or CO2 have a higher solubility and diffusion constant across the membrane?

Answer 40

CO2

Question 41

does CO2 or oxygen equilibrate quicker across the membrane?

Answer 41

CO2

Question 42

How much CO2 is in the alveolus and what does this allow?

Answer 42

not very much so CO2 can move down its pressure gradient from the blood to the alv to be expired

Question 43

what can CO2 be measured from and what is this?

Answer 43

end tidal volume - big breath out then capture the last bit (same as CO2 alveolar pressure)