Principles of gas exchange

Question 1

how does O2 and CO2 gas exchange occur

Answer 1

via simple diffusion

Question 2

what is the rate of diffusion equivalent to

Answer 2

to the surface area which is proportional to the pressure gradient

Question 3

what dependant factors are there on the efficiency of diffusion

Answer 3

thickness of the membrane, physiochemical properties

Question 4

what types of cells can you see by zooming into the alveoli with a microscope

Answer 4

capillaries in-between alveoli
red blood cells
simple squamous epithelia

Question 5

what is the pressure gradient definition in the lungs

Answer 5

the difference in partial pressure of the respective gases in the alveolus and the blood

Question 6

what is the partial pressure of gas in a mixture of gasses

Answer 6

the pressure that it would exert if it was the only gas in the container

Question 7

what is the universal gas equation

Answer 7

PV = nRT
P = pressure 
V = volume 
n = number of molecules 
R = universal gas constant 
T = absolute pressure

Question 8

what is the composition of air

Answer 8

78% nitrogen
21% oxygen
1% argon
0.04% carbon dioxide

Question 9

what is daltons law

Answer 9

the partial pressure of a gas in a gas mixture = total pressure x fractional concentration of the gas

Question 10

what is the difference in partial pressure of O2 CO2 and Nitrogen at 5000km

Answer 10

O2 21 - 11.8
CO2 0 - 0
Nitrogen 80 - 44.2

Question 11

why is the partial pressure of O2 in the alveoli lower than that in room air

Answer 11

inspired air humidified in the upper airway
in the alveoli oxygen is taken up while carbon dioxide is added the body consumes more O2 molecules than it produces CO2 (typically 1.25x)

Question 12

what dilutes the air coming into the lungs and therefore dropping the partial pressure of O2

Answer 12

CO2

Question 13

what is the respiratory quotient for 
CO2
protein 
carbs 
fat

Answer 13

lipids - 0.7
proteins - 0.8
carbs 1.0

Question 14

what is the saturated vapour pressure of water at 37 degrees

Answer 14

6.3 kPa

Question 15

how would you work out the fully humidified air, partial pressure of O2

Answer 15

(101.3 - 6.3) x 0.21 = 19.95 kPa

Question 16

what is the effect of CO2 on alveolar partial pressure of O2

Answer 16

a typical value of the alveolar partial pressure of CO2 is 5kPa
if one CO2 molecule was produced for every O2 molecule consumed the alveolar partial pressure of oxygen would be 19.95 - 5 = 14.95 kPa
but typically 1.25 x as many O2 molecules are consumed as CO2 molecules produced
thus alveolar partial pressure of O2 =

Question 17

in theory the kPa of O2 in the lungs should be 13.7 why is this not reality

Answer 17

lungs aren’t the perfect system
the blood is not always completely saturated and passes the lungs causing a shunt so its actually around 13.5 kPa and around 13.3 by the time it hits the body

Question 18

what is the diffusion distance in capillaries of the lungs

Answer 18

0.2 - 0.6 microns

Question 19

what is the partial pressure of gas in solution

Answer 19

it is inversely proportional to its solubility
ie the greater the solubility the more molecules can be accommodated for a given partial pressure ie low solubility = higher partial pressure

Question 20

what are the solubility differences between O2 and CO2

Answer 20

CO2 is 24x more soluble than O2

Question 21

why is CO2 transfer more efficient than O2

Answer 21

CO2 has a higher density, water solubility, diffusing capacity but higher partial pressure

Question 22

in a healthy person at rest how long does it take for O2 and CO2 to pass through capillaries

Answer 22

CO2 around 0.1 secs

O2 0.25 secs

Question 23

what happens to gas exchange in a healthy person during exercise

Answer 23

no shunting or partial oxygenation

blood passes through capillaries quicker and less O2 CO2 can transfer

Question 24

what are the partial pressures of O2 in:
non-oxygenated blood
alveoli
oxygenated blood

Answer 24

4. 3
5. 3
6. 3

Question 25

what happens to gas exchange in a patient with pulmonary fibrosis during exercise

Answer 25

diffusion of O2 across the alveoli is decreased due to alveoli thickening
kPa of O2 9.5

Question 26

what type of disease is fibrosis of the lungs

Answer 26

restrictive

normal CO2 but less O2

Question 27

what is the difference between type 1 or 2 respiratory failure

Answer 27

type 1 - hypoxic but normal CO2

type 2 - low O2 and high CO2

Question 28

what is the oxygen diffusing capacity =

Answer 28

oxygen uptake / (alveolar PO2 - mean pulmonary capillary PO2)

Question 29

what i set carbon monoxide diffusing capacity

Answer 29

carbon monoxide uptake / alveolar PCO

Question 30

what is the mean pulmonary capacity PCO

Answer 30

effectively 0 because of very high affinity for CO in haemoglobin

Question 31

what is the affinity difference between CO and O2

Answer 31

230 meow of CO

Question 32

how does pneumonia / pulmonary

Answer 32

lungs fill with fluid and puss and reduce gas exchange

Question 33

how does adult/acute respiratory distress syndrome affect gas exchange

Answer 33

there is shunt and ventilation - perfusion (VA/Q) inequality produced by fluid located in the interstitial space, alveolar collapse and flooding

Question 34

how does atelectasis affect the lungs

Answer 34

increased weight reduces lung compliance and reduced FRC