Gas Laws and Gas Transfer

Question 1

What are the 2 types of gas movement?

Answer 1

Mechanical force: bulk flow of air down concentration gradient. (Large airways and circulation)

Diffusion: Movement down the molecular concentration gradient of each individual gas. (Terminal bronchioles-> metabolising tissues)

Question 2

What is the kinetic theory of gases?

Answer 2

States that gas molecules are in constant random motion. Occupy small space, majority of space between them is empty space.
Pressure is generated by the force of molecules colliding with eachother and walls of container (harder and faster collisions= more collisions= higher pressure)

Question 3

What is Boyle’s Law?

Answer 3

Pressure is inversely proportional to volume if the temperature and volume of gas is constant.

Question 4

What is Charles’ Law?

Answer 4

Volume is directly proportional to temperature on the absolute temperature scale if pressure and amount of gas are constant.

Question 5

What is the universal gas law?

Answer 5

Volume= nRT/P
so PV=nRT

(n= number of moles of a gas, P=pressure, R=constant, T=temperature absolute degrees)

Question 6

What is Dalton’s Law?

Answer 6

Mixed unreactive gases behave independently, each exerting their own pressure = partial pressure.
In a mixture of gases, each gas exerts the same amount of pressure it would if it was occupying the same volume alone.

Question 7

Define equilibrium in adjacent gas and water in a closed system

Answer 7

When gas and water are adjacent, water will evaporate and gas will dissolve. Equilibrium is reached when the partial pressures of each substance on either side of the interface (i.e. alveolar membrane) are equal.

Equilibrium pressure of water vapour is the saturated vapour pressure.

Question 8

What is saturated pressure dependent on?

Answer 8

The temperature of the system: increases with increasing temperature as increased kinetic energy allows more vapour to escape liquid surface.

Question 9

What is Henry’s Law?

Answer 9

The physical amount of gas dissolving in a solvent is directly proportional to the pressure of the gas at the solvent’s surface.
This is expressed as the solubility of a gas

Question 10

Define solubility

Answer 10

The solubility of a gas in a given liquid represents its ability to dissolve in that liquid.

Question 11

Define gas tension

Answer 11

Gas tension indicates how readily a gas will evaporate from a liquid, based on the pressure it exerts inside the liquid. Measured as a partial pressure of the solute in a solvent.

(e.g. CO2 has higher gas tension in the blood in the alveolar capillaries than it has partial pressure in the alveoli therefore diffuses down its concentration gradient into the alveoli)

Question 12

Define content

Answer 12

The physical amount of a gas in a liquid:
Changes with temperature and the gas pressure above it
Proportional to both its solubility in the liquid and the gas tension at equilibrium.

Question 13

What is the final gas content at equilibrium dependent on?

Answer 13

Gas tension
Solubility of gas in the liquid
Avidity of Hb for oxygen

Question 14

What is diffusion proportional to?

Answer 14

Proportional to:

• The surface area of the alveoli
• Pressure gradient caused by different partial pressures

Inversely proportional to:
-The resistance to diffusion of the alveolar-capillary membrane

Question 15

What determines the resistance to diffusion of the alveolar-capillary membrane?

Answer 15

Nature of the membrane:
-Thickness from scarring = increased resistance

Nature of the gas:
-Solubility: gases diffuse at a rate proportional to their solubility
-Partial pressure
-

Question 16

What is the diffusion barrier comprised of?

Answer 16

Epithelial cell of alveolus
Tissue fluid and connective tissue
Endothelial cell of capillary
Plasma
Red blood cell membrane and cytoplasm

Question 17

Under normal circumstances, how is oxygen transfer to the tissues limited?

Answer 17

Perfusion limited:

Fully saturates Hb 25% along capillary bed, ability to take up more depends on perfusion of oxygen from Hb into tissues.

Question 18

How may oxygen transfer to tissues be limited in disease states?

Answer 18

Diffusion limited: cannot fully saturate Hb as quickly, ability of Hb to uptake oxygen is dependent on the amount being diffused across the diffusion barrier.