Diffusion of respiratory gases

Question 1

Atmospheric pressure

Answer 1

760 mmHg

597 (N2 pressure) + 159 (O2 pressure) + 0.3 (CO2 pressure) + 3.7 (H2O pressure) = 760
Dalton law - total of pressures of individual gases

Question 2

How does partial pressure of respiratory gases differ between atmospheric and alveolar air?

Answer 2

Question 3

Thickness of respiratory membrane

Answer 3

0.6 microns

Question 4

What are the components of the respiratory membrane?

Answer 4

Alveolar membrane
Interstitial fluid
Capillary wall

Question 5

Formula for calculating the diffusion of gases

Answer 5

D = (𝚫P x A x S)/(d x √MW)

𝚫P = pressure gradient
A = Cross-sectional area
S = Solubility of gas
d = Distance (thickness of respiratory membrane)
√MW = Molecular Weight of gas

Question 6

What is the diffusion coefficient?

Answer 6

Diffusion coefficient = S/√MW

Question 7

Diffusion coefficient of atmospheric gases

Answer 7

Question 8

What is nitrogen narcosis?

Answer 8

High pressures in deep sea diving causes nitrogen to dissolve in the body

Question 9

What are the factors affecting diffusion of gases across the respiratory membrane?

Answer 9

Factor 1: Pressure gradient
Factor 2: Surface area of the respiratory membrane
Factor 3: Nature and thickness of the respiratory membrane
Factor 4: Ventilation perfusion ratio (V/Q)

Question 10

How can partial pressure be calculated?

Factor 1: Pressure gradient

Answer 10

Partial pressure = Concentration of dissolved gases/Solubility coefficient

Question 11

Partial pressures of oxygen and carbon dioxde in the alveoli and venous blood

Factor 1: Pressure gradient

Answer 11

Question 12

What is the surface area of the respiratory membrane?

Factor 2: Surface area of the respiratory membrane

Answer 12

70m2

Question 13

What factors increase the surface area of the respiratory membrane?

Factor 2: Surface area of the respiratory membrane

Answer 13

Exercise opens closed pulmonary capillaries, dilates the capillaries and allows alveoli to expand

Question 14

What factors decrease the surface area of the respiratory membrane?

Factor 2: Surface area of the respiratory membrane

Answer 14

Lung disease (pneumonia, fibrosis, cancer)
Old age

Question 15

What factors can affect the nature and thickness of the respiratory membrane?

Factor 3: Nature and thickness of the respiratory membrane

Answer 15

Lung fibrosis → Change the nature of the respiratory membrane → Decrease gas diffusion
Pulmonary edema → Increase the thickness of the respiratory membrane → Decrease gas diffusion

Question 16

What factors increase the ventilation perfusion ratio?

Factor 4: Ventilation perfusion ratio

Answer 16

Pulmonary thrombi or emboli → less perfusion → decreased gas exchange.
Emphysema → high ventilation → decreased gas exchange.

Question 17

What factors decrease the ventilation perfusion ratio?

Factor 4: Ventilation perfusion ratio

Answer 17

Bronchial asthma → less ventilation → decreased gas exchange