Principles of gas exchange Flashcards
how does O2 and CO2 gas exchange occur
via simple diffusion
what is the rate of diffusion equivalent to
to the surface area which is proportional to the pressure gradient
what dependant factors are there on the efficiency of diffusion
thickness of the membrane, physiochemical properties
what types of cells can you see by zooming into the alveoli with a microscope
capillaries in-between alveoli
red blood cells
simple squamous epithelia
what is the pressure gradient definition in the lungs
the difference in partial pressure of the respective gases in the alveolus and the blood
what is the partial pressure of gas in a mixture of gasses
the pressure that it would exert if it was the only gas in the container
what is the universal gas equation
PV = nRT P = pressure V = volume n = number of molecules R = universal gas constant T = absolute pressure
what is the composition of air
78% nitrogen
21% oxygen
1% argon
0.04% carbon dioxide
what is daltons law
the partial pressure of a gas in a gas mixture = total pressure x fractional concentration of the gas
what is the difference in partial pressure of O2 CO2 and Nitrogen at 5000km
O2 21 - 11.8
CO2 0 - 0
Nitrogen 80 - 44.2
why is the partial pressure of O2 in the alveoli lower than that in room air
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)
what dilutes the air coming into the lungs and therefore dropping the partial pressure of O2
CO2
what is the respiratory quotient for CO2 protein carbs fat
lipids - 0.7
proteins - 0.8
carbs 1.0
what is the saturated vapour pressure of water at 37 degrees
6.3 kPa
how would you work out the fully humidified air, partial pressure of O2
(101.3 - 6.3) x 0.21 = 19.95 kPa
what is the effect of CO2 on alveolar partial pressure of O2
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 =
in theory the kPa of O2 in the lungs should be 13.7 why is this not reality
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
what is the diffusion distance in capillaries of the lungs
0.2 - 0.6 microns
what is the partial pressure of gas in solution
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
what are the solubility differences between O2 and CO2
CO2 is 24x more soluble than O2
why is CO2 transfer more efficient than O2
CO2 has a higher density, water solubility, diffusing capacity but higher partial pressure
in a healthy person at rest how long does it take for O2 and CO2 to pass through capillaries
CO2 around 0.1 secs
O2 0.25 secs
what happens to gas exchange in a healthy person during exercise
no shunting or partial oxygenation
blood passes through capillaries quicker and less O2 CO2 can transfer
what are the partial pressures of O2 in:
non-oxygenated blood
alveoli
oxygenated blood
- 3
- 3
- 3
what happens to gas exchange in a patient with pulmonary fibrosis during exercise
diffusion of O2 across the alveoli is decreased due to alveoli thickening
kPa of O2 9.5
what type of disease is fibrosis of the lungs
restrictive
normal CO2 but less O2
what is the difference between type 1 or 2 respiratory failure
type 1 - hypoxic but normal CO2
type 2 - low O2 and high CO2
what is the oxygen diffusing capacity =
oxygen uptake / (alveolar PO2 - mean pulmonary capillary PO2)
what i set carbon monoxide diffusing capacity
carbon monoxide uptake / alveolar PCO
what is the mean pulmonary capacity PCO
effectively 0 because of very high affinity for CO in haemoglobin
what is the affinity difference between CO and O2
230 meow of CO
how does pneumonia / pulmonary
lungs fill with fluid and puss and reduce gas exchange
how does adult/acute respiratory distress syndrome affect gas exchange
there is shunt and ventilation - perfusion (VA/Q) inequality produced by fluid located in the interstitial space, alveolar collapse and flooding
how does atelectasis affect the lungs
increased weight reduces lung compliance and reduced FRC
