Gas Exchange Flashcards
For a 70kg man, how much air is inhaled per min, how much reaches alveoli, how much of that is oxygen and how much oxygen diffuses into blood ?
6000ml inhaled
4200ml reaches alveoli
880ml is oxygen
250ml of oxygen diffuses into blood
Remaining 630ml exhaled along with 200ml carbon dioxide and 3300ml nitrogen
How much oxygen is consumed at rest and how much carbon dioxide is produced at rest ?
250ml oxygen consumed
200ml carbon dioxide produced
How many litres of oxygen are consumed per day ?
360
Why do gases mix?
Because of their random velocities of their molecules
How do gases move ?
By diffusion down their own concentration gradient- irrelevant of other gases
What is Dalton’s law ?
States that the pressure exerted by a mixture of gases is equal to the sum of the pressures that would be exerted by the individual gases occupying the same volume alone
If total air pressure is 760mmHg what is the pressure of oxygen in the atmosphere ?
760 * 0.21 = 160mmHg
What is ficks law of diffusion ?
States that’s the rate of diffusion of a gas through a sheet of tissue is directly proportional to the area, partial pressure difference and diffusion constant and inversely proportional to the tissue thickness
What is the diffusion constant ?
It is proportional to the gas solubility and inversely proportional to the square root of the molecular weight of the gas
How does ficks law relate to diffusion of gases across the respiratory membrane ?
Explains the rapid diffusion of gases across the membrane
Highlight importance of large partial pressure gradient
What 2 things happen to atmospheric air before it reaches alveoli ?
Mixes with air in dead space which is rich in carbon dioxide and deficient in oxygen
Becomes saturated with water vapour
Therefore alveolar air has a much higher carbon dioxide pressure and lower oxygen pressure compared to atmospheric
What happens to the partial pressure of oxygen at altitude ?
Decreases due to the decrease in barometric pressure
What happens to the oxygen diffusion gradient from atmosphere to alveoli to blood to tissue as altitude increases ?
Decreases So oxygen delivery is more difficult
What is Henry’s law ?
Amount of gas that dissolves in a liquid at equilibrium depends on both partial pressure of the gas in the gas mixture to which the liquid is exposed and on the specific solubility of that gas in that particular liquid
Why will the gas concentrations of 2 gases in a liquid not be the same if their partial pressures are the same ?
Because they have different solubilities in the liquid
Out of carbon dioxide and oxygen which is less soluble in water ?
Oxygen - 20times less
What happens to pressure as water depth increases ?
Increases - every 10m depth increase increase pressure by 1atm
At rest when does the diffusion of carbon dioxide and oxygen reach equilibrium at the lungs ?
Within the first third of time for blood to pass along length of pulmonary capillaries - complete within 0.25 seconds
Why is it important that gas exchange to equilibrium occurs by the first third of the length of the pulmonary capillaries ?
Because in severe exercise the transmit time can be reduced to about a third of the time so it means in normal individuals diffusion to equilibrium can still occur
What factors could decrease oxygen uptake at the lungs ?
Thickening of the blood-gas barrier due to disease and reduced alveolar oxygen pressure.
What ca cause pulmonary oedema ?
Abnormally high rate of capillary fluid filtration
Or
Impaired lymphatic drainage
What is a common cause of pulmonary oedema ?
L sided heart failure
Causes increased pulmonary venous and capillary pressures leading to hydrostatic oedema
What is interstitial oedema ?
Accumulation of excessive fluid in interstitial space in lungs
What is alveolar oedema ?
Fluid accumulates within alveoli and this interfere with breathing
- increases effective thickness of respiratory membrane
- interfere with action of pulmonary surfactant decreasing lung compliance and increasing work of breathing
What are the symptoms of alveolar oedema ?
Rapid shallow breathing, hypoxia and cyanosis
The alveolar partial pressure of oxygen and carbon dioxide are determined by 3 factors, what are they ?
The pressure of both gases in the inspired air
Volume of fresh air reaching alveoli each min
Rates at which respiring tissue is consuming the oxygen and producing the carbon dioxide
