Gas Exchange

Question 0

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 ?

Answer 0

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

Question 1

How much oxygen is consumed at rest and how much carbon dioxide is produced at rest ?

Answer 1

250ml oxygen consumed

200ml carbon dioxide produced

Question 2

How many litres of oxygen are consumed per day ?

Answer 2

360

Question 3

Why do gases mix?

Answer 3

Because of their random velocities of their molecules

Question 4

How do gases move ?

Answer 4

By diffusion down their own concentration gradient- irrelevant of other gases

Question 5

What is Dalton’s law ?

Answer 5

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

Question 6

If total air pressure is 760mmHg what is the pressure of oxygen in the atmosphere ?

Answer 6

760 * 0.21 = 160mmHg

Question 7

What is ficks law of diffusion ?

Answer 7

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

Question 8

What is the diffusion constant ?

Answer 8

It is proportional to the gas solubility and inversely proportional to the square root of the molecular weight of the gas

Question 9

How does ficks law relate to diffusion of gases across the respiratory membrane ?

Answer 9

Explains the rapid diffusion of gases across the membrane

Highlight importance of large partial pressure gradient

Question 10

What 2 things happen to atmospheric air before it reaches alveoli ?

Answer 10

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

Question 11

What happens to the partial pressure of oxygen at altitude ?

Answer 11

Decreases due to the decrease in barometric pressure

Question 12

What happens to the oxygen diffusion gradient from atmosphere to alveoli to blood to tissue as altitude increases ?

Answer 12

Decreases So oxygen delivery is more difficult

Question 13

What is Henry’s law ?

Answer 13

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

Question 14

Why will the gas concentrations of 2 gases in a liquid not be the same if their partial pressures are the same ?

Answer 14

Because they have different solubilities in the liquid

Question 15

Out of carbon dioxide and oxygen which is less soluble in water ?

Answer 15

Oxygen - 20times less

Question 16

What happens to pressure as water depth increases ?

Answer 16

Increases - every 10m depth increase increase pressure by 1atm

Question 17

At rest when does the diffusion of carbon dioxide and oxygen reach equilibrium at the lungs ?

Answer 17

Within the first third of time for blood to pass along length of pulmonary capillaries - complete within 0.25 seconds

Question 18

Why is it important that gas exchange to equilibrium occurs by the first third of the length of the pulmonary capillaries ?

Answer 18

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

Question 19

What factors could decrease oxygen uptake at the lungs ?

Answer 19

Thickening of the blood-gas barrier due to disease and reduced alveolar oxygen pressure.

Question 20

What ca cause pulmonary oedema ?

Answer 20

Abnormally high rate of capillary fluid filtration
Or
Impaired lymphatic drainage

Question 21

What is a common cause of pulmonary oedema ?

Answer 21

L sided heart failure

Causes increased pulmonary venous and capillary pressures leading to hydrostatic oedema

Question 22

What is interstitial oedema ?

Answer 22

Accumulation of excessive fluid in interstitial space in lungs

Question 23

What is alveolar oedema ?

Answer 23

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

Question 24

What are the symptoms of alveolar oedema ?

Answer 24

Rapid shallow breathing, hypoxia and cyanosis

Question 25

The alveolar partial pressure of oxygen and carbon dioxide are determined by 3 factors, what are they ?

Answer 25

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