Lecture 4 - Principles of gas exchange

Question 1

How are O2 andCO2 eliminated from the blood?

Answer 1

through simple diffusion

Question 2

rate of diffusion is…

Answer 2

proportional to the surface area and pressure gradient

Question 3

what is diffusion also dependent on

Answer 3

on the physiochemical properties of the gas and nature of the membrane (thickness etc)

Question 4

What is lung tissue made of

Answer 4

simple squamous epithelial cells

Question 5

What is pressure gradient

Answer 5

difference in the partial pressures of the respective gases in the alveolus and the blood.
partial pressure of a gas in a mixture of gases is the pressure it would exert it is was the only gas in the contained

Question 6

Universal gas equation

Answer 6

pV=nRT

Question 7

What is daltons law

Answer 7

The partial pressure of a gas in a gas mixture = Total pressure x fractional concentration of a gas

Question 8

Partial pressures of gases in the atmosphere

Answer 8

Nitrogen - 79% PP at high altitude - 44.2
Carbon dioxide - always 0
Oxygen - 215 and at high pp 11.8%

Question 9

Why is partial pressure of oxygen in alveoli less than in room air?

Answer 9

inspired air is humidified in the upper airway
In the alveoli, oxygen is taken up while co2 is added/
body consumed more o2 molecules than it produces CO2

Question 10

At 37 degrees celcius, the saturated vapour pressure of water is?

Answer 10

6.3 kPa that is also the partial pressure

Question 11

What is the partial pressure of oxygen in fully humidified air at 37 degrees celcius

Answer 11

[101.3 (total partial pressure at sea level) - 6.3 (PP of water)] x 0.21 (fraction concentration of oxygen = 19.95 kPa . this is less than atmospheric partial pressure

Question 12

What is the effect of CO2

Answer 12

co2 decreases alveolar partial pressure of oxygen further as 1.25x as many O2 molecules are consumed as CO2 molecules produced.
Alveolar partial pressure of oxygen = 19.95 - (1.25x5) = 13.7 kPa

Question 13

Alveolar partial pressure of CO2

Answer 13

5 kPa

Question 14

What is the relationship between partial pressure and solubility

Answer 14

partial pressure of a gas in solution is inversely proportional to its solubility. greater the solubility, more molecules can be accommodated for a given partial pressure

Question 15

Compare CO2 solubility to that of oxygen

Answer 15

it is 24 times more soluble than oxygen

Question 16

Rate of diffusion of O2 and CO2

Answer 16

In theory, CO2 transfer is much more efficient than O2 transfer

Question 17

What happens when the blood is non-oxygenated in a healthy person at rest in terms of partial pressures

Answer 17

PO2 is less hence there is more solubility - 5.3kPa

PCO2 is 6.1 kPa which is more than oxygen so it leaves the blood to the alveoli to get oxygenated

Question 18

What happens to partial pressures when the co2 leaves the blood to enter the aveoli and oxygen re-enters the blood

Answer 18

the partial pressure of oxygen increases as oxygenated diffuses back into the blood and co2 leaves it
so the reoxygenated blood has same partial pressures as the alveoli -
p02= 13.3 kPa and PCO2 = 5.3 kPa

Question 19

what happens to partial pressures in a healthy person during exercise

Answer 19

po2 of non-oxygenated blood is less than at rest - 4.3 kPa

Oxygen enters blood from alveoli to reinstate partial pressure to 13.3 kPa

Question 20

what happens to partial pressures in a person with pulmonary fibrosis during exercise

Answer 20

the partial pressure of oxygen in non-oxygenated blood is still less - 4.3 kPa
Due to alveolar thickening during pulmonary fibrosis, there is less diffusion of oxygen back into the blood and so pO2 = 9.5 kPa

Question 21

Clinical measurement of diffusing capacity

Answer 21

oxygen diffusing capacity = oxygen uptake/ (alveolar pO2 - mean pulmonary capillary pO2)

Question 22

What is carbon monoxide diffusing capacity

Answer 22

carbon monoxide uptake /alveolar Pco
mean pulmonary capillary PC0 is effectively zero because of its high affinity for haemoglobin and thats why it is not there in the equation

Question 23

Alveolar capillary destruction is

Answer 23

emphysema

Question 24

Alveolar collapse

Answer 24

atelactasis

Question 25

Thickening of the alveolar wall

Answer 25

alveolar fibrosis

Question 26

Alveolar consolidation (filling with liquid can be due to swelling caused by infection)

Answer 26

pneumonia

Question 27

Frothy secretions

Answer 27

pulmonary edema