Gas exchange

Question 1

What 4 factors affect gas exchange?

Answer 1

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

Question 2

What is dead space?

Answer 2

Areas of the lungs that are ventilated but not perfused

Question 3

What is anatomic dead space?

Answer 3

Tree of the trachea, bronchi and bronchioles that don’t participate in respiration

Question 4

What is alveolar dead space?

Answer 4

Caused by ventilation/perfusion mismatch in which the gases haven’t been exchanged

Question 5

What is physiological dead space?

Answer 5

Alveolar dead space + Anatomical 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 and this is pulled into the alveoli during inspiration. During expiration the first air expelled is dead air

Question 7

What is the difference in the composition of air in the trachea compared to dry air?

Answer 7

In the trachea the air is moist so the partial pressure of water increases and the partial pressure of oxygen decreases

Question 8

What is the difference in the composition of air in the alveolar compared to dry air?

Answer 8

Partial pressure of oxygen decreases and partial pressure of CO2 increases due to the mixing of old and new air

Question 9

Why does venous blood have a reduced partial pressure compared to arterial blood or dry air and why is this useful?

Answer 9

we produce less CO2 for the same amount of oxygen used due to the respiratory quotient of the metabolites. This is useful because it allows pneumothorax to resolve spontaneously because gases will move from a high to low concentration, so fluid in pneumothorax will drain into venous circulation

Question 10

What is Dalton’s law?

Answer 10

Gases contribute to pressure according to the percentage of composition

Question 11

Is CO2 more soluble than O2?

Answer 11

Yes by 20x

Question 12

If oxygen and CO2 were in different compartments at the same partial pressure which one would have the higher net amount of molecules?

Answer 12

CO2 would have higher amount because it is more soluble

Question 13

How is the diffusion capacity of the lung optimised?

Answer 13

By the cell shape of the alveolar cell type I and fused basement membrane

Question 14

What does the diffusion capacity of the lung dependent on?

Answer 14

The nature of the tase –> solubility

Question 15

What are the 2 reasons for limited gas transfer?

Answer 15

Diffusion and perfusion

Question 16

How does diffusion limit gas transfer?

Answer 16

Inefficient transfer from the gas to liquid phase

Question 17

How does perfusion limit gas transfer?

Answer 17

Blood doesn’t take away gases down the concentration gradient quick enough. Not enough blood to carry away the transferred gas

Question 18

Is oxygen diffusion or perfusion limited and why?

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 diffusion or perfusion limited and why?

Answer 19

Diffusion limited

It isn’t transferred quick enough

Question 20

What affect does COPD have not he microstructure of the lung?

Answer 20

Affects how the alveoli are ventilated so there is a lower concentration of oxygen and higher concentration of CO2 so there is a lower concentration gradient between the lungs and the blood so there is reduced gas exchange