Gas exchange

Question 1

What factors affect gas exchange in the lungs?

Answer 1

Surface area if alveoli
Thickness if the membrane (diffusion distance)
Concentration gradient
Solubility of the gas

Question 2

What is the dead space?

Answer 2

Areas in the alveoli in which it is ventilated but not perfused - no gas exchange takes place

Question 3

What is anatomic dead space?

Answer 3

Dead spaces in structures that don’t participate in respiration e.g. tree of trachea, bronchi and bronchioles

Question 4

What is alveolar dead space?

Answer 4

Caused by ventilation/perfusion mismatch. Made up of gases that haven’t been exchanged

Question 5

What is physiological dead space?

Answer 5

Anatomical dead space + alveolar dead space

Question 6

What are the consequences of dead space?

Answer 6

At the end of expiration the dead space is filled with bad air.
This is pulled into the alveoli during inspiration
During expiration the first air expelled is dead space.

Question 7

How does the composition of air differ in the trachea from the atmospheric air?

Answer 7

In the trachea the air is moist. So partial pressure of H2O increases and partial pressure of oxygen decreases due to humidification

Question 8

How does composition of air differ int he alveolar compared to the atmospheric air?

Answer 8

Partial pressure of O2 decreases and PCO2 increases due to the mixing of old and new air

Question 9

Why does venous blood have a reduced partial pressure?

Answer 9

To allow pneumothorax to resolve spontaneously because gases can move from a high to a low pressure –> atmospheric pressure in pneumothorax so the extra fluid will be drawn out

Question 10

What causes venous blood to have a lower pressure?

Answer 10

Produce less CO2 for the same amount fo oxygen used due to the respiratory quotient of the metabolites

Question 11

What is Dalton’s law?

Answer 11

Gases contribute to pressure according to the percentage of composition

Question 12

Is CO2 or O2 more soluble?

Answer 12

CO2 is 20x more soluble

Question 13

In 2 compartments filled with oxygen or CO2 where the partial pressures are equal which compartment will have more molecules of gas and why?

Answer 13

More CO2 than O2 because it is more soluble than O2

Question 14

What optimises the diffusion capacity of the lung?

Answer 14

The cell shape of the alveolar cell type 1 and the fused basement membrane

Question 15

What 2 factors can limit gas transfer?

Answer 15

Diffusion and perfusion

Question 16

How can diffusion cause a limit to gas transfer?

Answer 16

Inefficient transfer from the gas phase to the liquid phase.

Question 17

How can perfusion cause a limit to gas transfer?

Answer 17

Blood doesn’t take gases away down concentration gradient - not enough blood to carry away the transferred gas

Question 18

Is oxygen perfusion or diffusion limited?

Answer 18

Perfusion limited.

Reaches equilibrium before the end of the capillary so it can’t be carried away quick enough

Question 19

Is CO2 perfusion or diffusion limited?

Answer 19

Diffusion limited.

It isn’t transferred quick enough