Gas exchange

Question 1

What is meant by anatomical dead space?

Answer 1

Air that remains in the airways, where it is not available for gas exchange

Question 2

What is the calculation for pulmonary ventilation?

Answer 2

Pulmonary ventilation = Tidal volume x Respiratory rate

Question 3

What is the calculation for alveolar ventilation?

Answer 3

Alveolar ventilation = (Tidal volume - Dead space volume) x Respiratory rate

Question 4

What is meant by pulmonary ventilation?

Answer 4

The volume of air breathed in and out per minute

Question 5

What is meant by alveolar ventilation?

Answer 5

The volume of air exchanged between the atmosphere and alveoli per minute

Question 6

How is pulmonary ventilation increased?

Answer 6

Both depth and rate of ventilation increases, however, because of the dead space, it is more advantageous to increase the depth of breathing

Question 7

What does the transfer of gases between the body and atmosphere depend upon?

Answer 7

Ventilation - Rate of gas passage through lungs
Perfusion - Rate of blood passage through lungs

Question 8

What occurs when CO2 concentration increases in an area of the lungs?

Answer 8

Airways dilate to increase airflow out of the lungs

Question 9

What occurs when O2 concentration decreases in an area of the lungs?

Answer 9

Blood vessels constrict to decrease blood flow

Question 10

What occurs when CO2 concentration decreases in an area of the lungs?

Answer 10

Airways constrict to decrease airflow out of the lungs

Question 11

What occurs when O2 concentration increases in an area of the lungs?

Answer 11

Blood vessels dilate to increase blood flow

Question 12

What is meant by alveolar dead space?

Answer 12

Ventilated alveoli which are not adequately perfused with blood

Question 13

What 2 things make up physiological dead space?

Answer 13

Anatomical dead space + Alveolar dead space

Question 14

What 4 factors influence rate of gas exchange across the alveolar membrane?

Answer 14

Partial pressure gradient of CO2 and O2
Diffusion coefficient of CO2 and O2
Surface area of alveolar membrane
Thickness of alveolar membrane

Question 15

What is meant by partial pressure?

Answer 15

In a mixture of gases 1 and 2, the partial pressure of gas 1 is the pressure that it would exert if it occupied the total volume of the mixture, in the absence of gas 2

Question 16

How is the partial pressure of a gas calculated?

Answer 16

PP = %gas/100 x total volume

Question 17

What is Dalton’s law of partial pressure?

Answer 17

The total pressure exerted by a gaseous mixture is equal to the sum of the partial pressure of each individual component in a gas mixture
Total = P1 + P2 + … + Pn

Question 18

What is the calculation for partial pressure of O2 in alveolar air (PAO2)?

Answer 18

PAO2 = PiO2 - [PaCO2 ÷ 0.8]
PiO2 is the partial pressure of O2 in inspired air
PaCO2 is the partial pressure of CO2 in arterial blood
0.8 is the respiratory exchange ratio

Question 19

How does the partial pressure gradient of O2 differ from the partial pressure gradient of CO2?

Answer 19

The partial pressure gradient is much larger for O2 than that of CO2
This is because CO2 is much more soluble in membranes than O2 (It has a 20x greater diffusion coefficient)

Question 20

What is meant by a gases diffusion coefficient?

Answer 20

The solubility of a gas in a membrane

Question 21

What is Fick’s law of diffusion?

Answer 21

The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet, but is inversely proportional to its thickness

Question 22

What cells make up the alveolar membrane?

Answer 22

Their walls contain a single layer of flattened type I alveolar cells
There are some type II alveolar cells that produce surfactant