3. Properties Of Gases

Question 1

What is Boyle’s law?

Answer 1

Pressure of a gas is inversely proportional to its volume.

Question 2

What does the sum of the partial pressures of the individual gases equal in a mixture of non-reacting gases?

Answer 2

Total pressure exerted.

Question 3

In a mixture of gases, what partial pressure does each gas exert?

Answer 3

A partial pressure equal to the pressure it would exert if it was the only gas present.

Question 4

What is atmospheric pressure at sea level?

Answer 4

101 kPa.
1 ATM.
760 mmHg.

Question 5

Is atmospheric pressure higher or lower than at sea level at high altitudes?

Answer 5

High altitudes - atmospheric pressure lower.

Question 6

What percentage of atmospheric air is oxygen?

Answer 6

20.9%

Question 7

What percentage of atmospheric air is nitrogen?

Answer 7

78%.

Question 8

What percentage of atmospheric air is carbon dioxide?

Answer 8

0.03%.

Question 9

In the body, what direction to gases diffuse in?

Answer 9

From an area of high partial pressure to an area of low partial pressure.

Question 10

What happens when inspired gases come into contact with body fluids?

Answer 10

Gas molecules will enter water to dissolve in liquid, and water molecules evaporate to enter the air.

Question 11

What force so water molecules entering the air exert?

Answer 11

Vapour pressure.

Question 12

What is the air saturated with when water molecules leave and enter the water at the same rate?

Answer 12

Air is saturated with vapour. So inhaled air becomes saturated with water in the upper respiratory tract.

Question 13

What is the saturated vapour pressure (SVP) at body temperature?

Answer 13

6.28 kPa.

Question 14

How would you calculate the pressure of the rest of the gases in moist air?

Answer 14

101-6.28=94.72 kPa.

Question 15

Are gases still in the same ratios in moist air as they are in dry air?

Answer 15

Yes, are still in the same ratios.

Question 16

How would you calculate the partial pressure of a gas in moist air?

Answer 16

pGas = (atmospheric pressure-6.28) x %Gas

Question 17

When is equilibrium of gas exchange reached?

Answer 17

When the rate of gas molecules entering water equals the rate of gas molecules leaving the water.
So the partial pressure of the gas in the liquid equals the partial pressure of the gas in the air above it.

Question 18

If a gas reacts (eg O2 binding to Hb) with a component of the liquid in addition to dissolving, what needs to happen before partial pressure is established?

Answer 18

The reaction must complete.

Question 19

What happens when oxygen enters the blood?

Answer 19

O2 enters the plasma and dissolves in it.
The dissolved O2 enters the RBC’s to bind to Hb.
This process continues until the Hb is fully saturated.
After the Hb is fully saturated, the O2 continues to dissolve until equilibrium is reached.
At equilibrium, the pO2 of plasma = the pO2 of alveolar air.

Question 20

What is pO2 of the blood a measure of?

Answer 20

The dissolved O2 in the blood.

Question 21

What happens as dissolved O2 diffuses into tissues down its partial pressure gradient?

Answer 21

As dissolved O2 leaves the blood, it is replaced by O2 bound to Hb.

Question 22

What is arterial pO2?

Answer 22

13.3 pKa

Question 23

What is arterial pCO2?

Answer 23

5.3 kPa.

Question 24

Why is the pO2 in alveolar air lower than in atmospheric air, and the pCO2 higher?

Answer 24

Inhale air has mixed with residual volume as well as the O2 being taken up and CO2 being given up by the pulmonary capillary blood.

Question 25

What causes decompression sickness in divers?

Answer 25

Pressure below sea level is both the atmospheric pressure plus the weight of the water. So the air inspired from a scuba tank during a dive is at higher pressure than on dry land. The pO2 and pN2 is higher, and so nitrogen moves from the high pressure in the lungs into the blood where there is low pressure. Swimming up to the surface too quickly doesn’t give the nitrogen enough time to leave the blood, and instead it can form painful bubbles. Symptoms are different in each person.

Question 26

What factors affect the diffusion rate of a gas in a fluid?

Answer 26

Pressure difference.
Solubility of the gas in solution.
The cross-sectional area of the fluid.
The distance the molecules must diffuse.
The molecular weight of the gas.
The temperature of the fluid (assume 37degreesC in body).

Question 27

Why, in a diseased lung, is oxygen gas exchange more impaired than carbon dioxide exchange?

Answer 27

Oxygen has a slower diffusion rate as is less soluble.

Question 28

When might the thickness of the membrane be affected, thus affecting the rate of gas diffusion through the respiratory membrane?

Answer 28

Increase in thickness as a result of oedema fluid in the interstitial space and in the alveoli.
Increase in thickness of alveolar membrane due to fibrotic lung disease.

Question 29

When might the surface area of the membrane be affected, thus affecting the rate of gas diffusion through the respiratory membrane?

Answer 29

Decreased surface area by removal of an entire lung.

Alveoli combining, decreasing surface area in emphysema.

Question 30

What is a ventilation perfusion mismatch?

Answer 30

How changes in the ventilation and perfusion ratio effects the concentrations of O2 and CO2 in the alveoli and blood during respiration.

Question 31

What is the ventilation perfusion ratio in the average person?

Answer 31

Usually 1.

Alveolar ventilation per minute = 4.9 L/minute and cardiac output - 5 L/minute.

Question 32

What causes anatomical dead space in the lungs?

Answer 32

Volume of the airways where no gas exchange occurs.

Question 33

What causes distributive dead space in the lungs?

Answer 33

Dead or damaged alveoli and alveoli with poor perfusion.

Question 34

What is physiological dead space?

Answer 34

Anatomical (serial) dead space and distributive dead space.