Gas Exchange

Question 1

external respiration

Answer 1

exchange of oxygen in the alveoli

exchange of carbon dioxide in the alveoli

Question 2

internal respiration

Answer 2

exchange of oxygen in the tissues

exchange of carbon dioxide in the tissues

Question 3

atmospheric pressure

Answer 3

partial pressure of gases in the atmosphere

Question 4

Dalton’s law

Answer 4

total pressure of mixture of non reacting gases is the sum of partial pressures exerted by each of the gases in the mixture

Question 5

Henry’s law

Answer 5

amount of gas in solution depends on the partial pressure of the gas and its solubility
carbon dioxide in the air has a low pp but high solubility
oxygen has a lower solubility but a higher partial pressure

Question 6

Henry’s law- diffusion

Answer 6

movement of gas molecules from an area where the gas exerts a high pp to an area where it exerts a low pp
depends on temperature, movement of molecules
partial pressure of the gas in 2 areas

Question 7

Henry’s law- movement of gases

Answer 7

Gas moves along the conducting zone by bulk flow so pressure decreases as a whole
in the respiratory zone gas moves by diffusion. Temperature, partial pressure and solubility move at different pressures

Question 8

Fick’s law factors contributing to rate of diffusion

Answer 8

surface area/area of the barrier, decreased SA will collapse which will < ability to diffuse
diffusing ability of gas
inversely proportional to thickness of barrier
partial pressure difference

Question 9

Alveoli and capillary interface

Answer 9

oxygen dissolves and diffuses through surfactant
through alveoli wall
through capillary wall
into plasma
into RBCs and combines with haemoglobin
carbon dioxide goes the other way

Question 10

alveolar carbon dioxide exchange

Answer 10

mixed venous blood contains 45 mmHg partial pressure of carbon dioxide
alveolar partial pressure of carbon dioxide is 40mmHg
small gradient between 2 partial pressures
carbon dioxide is more soluble and reaches equilibrium in 0.25 seconds

Question 11

Capillary and tissue interface

Answer 11

bulk flow of blood to the tissues 
diffusion through RBC wall
through plasma
through tissue membrane 
into mitochondria

Question 12

Alveolar oxygen exchange

Answer 12

mixed venous blood contains 40mmHg partial pressure of oxygen
alveoli air contains 104 mmHg partial pressure of oxygen
movement of oxygen from the alveoli to the venous blood occurs
equilibrium takes 0.25 seconds

Question 13

oxygen exchange

Answer 13

oxygen combined with haemoglobin does not contribute to the partial pressure within capillary blood
once the haemoglobin is saturated, oxygen in plasma contributes to partial pressure, which then equals the alveolar partial pressure
transfer of oxygen is perfusion limited by lack of blood supply

Question 14

oxygen exchange in exercise

Answer 14

blood moves quickly through the capillaries
no limit on diffusion or perfusion as capillaries are recruited
partial pressure maintained
breathing deeper so increases SA

Question 15

oxygen exchange in disease

Answer 15

patient with abnormal alveolar/capillary interface
thickness of barrier has increased
diffusion of oxygen is reduced
may suffer diffusion limitation at rest which limits exercise tolerance
equilibrium isn’t happening fast enough so SA decreases