Ventilation and Diffusion Flashcards
What is Dalton’s Law?
A mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases
What is atmospheric pressure?
760mmHg
If oxygen makes up 21% of the gas in air, what is its partial pressure?
159mmHg- 21% of 760mmHg
What is used to give oxygen as it is toxic at high levels?
Given with inert gases such as nitrogen and helium
This reduces its partial pressure
What is Henry’s Law?
Henry’s Law states that the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid
What is the ratio of dissolving if the partial pressure of a gas increases from 1kPa to 10kPa above a solution?
Increases by 10x
What happens if the partial pressure in a liquid is greater than the air?
Gas will move out of the liquid
What is the absolute level of gas dissolved dependent on?
Depends on the solubility of the gas
Explain the difference In solubility of gases and that relation to partial pressures?
Carbon dioxide is most soluble with oxygen around 1/20th as soluble
Nitrogen is barely soluble in atmospheric pressure despite having the highest partial pressure
This is down to solubility in liquids
When does nitrogen in blood become a problem?
During deep diving where the partial pressure increases so much, nitrogen is forced into the blood
Why is atmospheric position not seen in alveoli?
Conducting passageways humidify the air and moistened
Pressure drops to 713mmHg
What must oxygen do once it enters the alveoli?
Dissolve in the aqueous layer
Diffuse across the membranes
Enter the blood
What is the rate of diffusion proportional to?
Surface area
Solubility
Concentration gradient
What is rate of diffusion inversely proportional to?
Tissue thickness
Square root of molecular mass
What is the surface area of the lungs?
50-100m2
What Is the difference between the partial pressures of oxygen between the alveolar air and the venous blood?
104mmHg
40mmHg
At rest, how long does it take for blood to pass through pulmonary capillaries?
1 second
In exercise, how long does it take for blood to pass through pulmonary capillaries?
0.3s
What are the different partial pressures of carbon dioxide between the alveolar air and the venous blood?
Alveolar is 40mmHg
Venous is 45mmHg
How does oedema effect diffusion?
Thickeness of membrane increases
This means full transit time may not be sufficient to complete gas exchange
This has a greater effect on oxygen as carbon dioxide is more soluble
How does emphysema effect diffusion?
Gas exchange is reduced to the surface area decreasing
What is gas movements in tissues?
In reverse
Movement of gases in opposite direction than in the lungs
CO2 moves into blood from tissues
Oxygen moves out of blood into tissues
What differences occur in high altitudes?
Atmospheric pressure is reduced so partial oxygen pressure is reduced
Haemoglobin saturation is reduced and there is an increase release of erythropoietin
What are the different pressures in Denver?
Atmospheric pressure is 632 mmHg (down from 760 mmHg)
Inspired PO2 – 125 mmHg (down from 149 mmHg)
Alveolar PO2 – 84 mmHg (down from 104 mmHg)
Alveolar PCO2 – 34 mmHg (down from 40 mmHg)
How does the body compensate for high altitudes?
Average male haemoglobin rises from 150g/l to 190 g/l
How does diving change breathibg?
Atmospheric pressure increases by 1 atmosphere every 10m depth
Air enters lung at increased pressure which forces nitrogen into the blood stream
As you then ascend to the surface gas bubbles of nitrogen starts to form
What problems occur with nitrogen bubbles?
Can form lethal emboli
Bubbles in the pulmonary circulation
Joins are extremely painful
Strokes
Decompression sickness
How do we treat someone with nitrogen poisoning?
Hyperbaric chambers to slowly decompress divers who come up too quickly
What occurs when someone rapidly ascends without exhaling?
As you move to shallow water, atmospheric pressure decreases
Volume of air in the lungs increases
This causes ruptures of alveoli and gas bubbles enter circulation (arterial gas embolism)
Usually lodge in cerebral circulation
Can cause seizures, fits, unconsciousness
How long does it take for full gas exchange of oxygen?
- 25s
0. 75s to pass through capillary bed
What is the oxygen and carbon dioxide pressures in the alveoli?
104mmHg lower- O2
40mmHg higher
Why does carbon dioxide pressure increase in the alveoli?
There is left over air after expiration