Lecture 18: O2 and CO2 EXCHANGE

Question 1

What is the formula for respiratory minute volume?

Answer 1

Tidal volume x respiratory rate

Question 2

What are the units of respiratory minute volume?

Answer 2

L/min

Question 3

What are the units of tidal volume?

Answer 3

L/breath

Question 4

What are the units of respiratory rate?

Answer 4

Breaths/min

Question 5

What is tidal volume also known as?

Answer 5

Breathing strength

Question 6

What is respiratory rate also known as?

Answer 6

Breathing speed

Question 7

Can all the respiratory minute volume be used?

Answer 7

No, some of the air never gets to the alveoli and so cannot gas exchange

Question 8

What is the air which can’t gas exchange called?

Answer 8

Dead space (Vd)

Question 9

How much is dead space?

Answer 9

About 150mL

Question 10

What is dead space interpreted as?

Answer 10

About 150mL of each breath just fills upper airways (conducting airways) and is of no use for gas exchange

Question 11

What is really important?

Answer 11

The amount of air that gets into the alveoli (alveolar ventilation)

Question 12

What is the formula for alveolar ventilation?

Answer 12

(tidal volume - dead space) x respiratory rate

Question 13

What are the units of dead space?

Answer 13

L/breath

Question 14

What is dead space also known as?

Answer 14

Air that can’t be used. It is constant

Question 15

What does each gas do in a gas mixture (air?

Answer 15

Exert its own own individual pressure, called a partial pressure

Question 16

What is the pressure of a mixture of gases equal to?

Answer 16

The sum total of the pressures of each individual gas

Question 17

What is inhaled air?

Answer 17

Dry and as it becomes filled with water vapour and moistened, the partial pressure of nitrogen and oxygen decrease

Question 18

What is the goal?

Answer 18

To move gas back and forth between the alveoli and the capillaries

Question 19

Where is inhaled oxygen transported?

Answer 19

Into the capillaries

Question 20

Where is carbon dioxide transported?

Answer 20

Into the alveoli to be exhaled

Question 21

Where do gases move?

Answer 21

Across the membranes between the alveoli and the capillaries by diffusion

Question 22

What determines rate of diffusion?

Answer 22

Surface area of the membranes, thickness of the membranes and pressure difference between the two sides

Question 23

What is the formula for flux (amount flowing)?

Answer 23

F=(A/T)*D(P1-P2)

Question 24

What is A?

Answer 24

Surface area

Question 25

What is T?

Answer 25

Thickness

Question 26

What is diffusion constant?

Answer 26

D

Question 27

What os P1-P2?

Answer 27

Pressure difference

Question 28

What does the diffusion constant depend on?

Answer 28

Gas solubility (S) and its molecular weigth

Question 29

How do carbon dioxide and oxygen differ in diffusion speed?

Answer 29

On a per molecule basis, carbon dioxide diffuses about 20 times faster than oxygen due to higher solubility of carbon dioxide

Question 30

Does diffusion constant affect flux?

Answer 30

Not usually

Question 31

What is the surface area?

Answer 31

Bulbous structure of alveoli and the high density of capillaries creates lots of surface area for gas exchange

Question 32

What is emphysema?

Answer 32

A disease characterised by dilation of the alveolar spaces and destruction of the alveolar walls

Question 33

What does reduction in surface area mean?

Answer 33

Less contact between the air and capillaries so oxygen exchange is greatly reduced

Question 34

What is the relationship between flux and thickness?

Answer 34

Flux is inversely proportional to thickness

Question 35

What is the blood air barrier mostly comprised of?

Answer 35

The alveolar and capillary walls

Question 36

What is the distance between the alveolar air and the blood?

Answer 36

Very small

Question 37

What happens in pulmonary fibrosis?

Answer 37

Thicker walls so diffusion decreases

Question 38

What does gas transfer by diffusion depend on?

Answer 38

Alveolar area for diffusion and thickness of alveolar membrane

Question 39

What is the main factor of gas transfer by diffusion?

Answer 39

Pressure difference is driven by diffusion (alveolar - arterial)

Question 40

What does alveolar partial pressure of oxygen depend on?

Answer 40

Partial pressure of oxygen in inspired air, alveolar ventilation and oxygen consumption - blood oxygen

Question 41

What is most important in alveolar partial pressure of oxygen?

Answer 41

Balance between oxygen consumption and alveolar ventilation because the atmospheric partial pressure of oxygen is usually constant

Question 42

What does low activity do to blood oxygen?

Answer 42

Reduced oxygen consumption by cells so higher levels of oxygen in the venous blood

Question 43

What does high activity do to blood oxygen?

Answer 43

Increased oxygen consumption by cells so lower levels of oxygen in the venous blood

Question 44

What does alveolar partial pressure of carbon dioxide depend on?

Answer 44

Partial pressure of carbon dioxide in inspired air, alveolar ventilation and carbon dioxide production

Question 45

What is alveolar partial pressure of carbon dioxide usually determined by?

Answer 45

The balance between carbon dioxide production and alveolar ventilation because atmospheric partial pressure of carbon dioxide is negligible

Question 46

What is the partial pressure of oxygen in the capillaries and alveolus?

Answer 46

It is high in the alveolus and low in the capillary

Question 47

Where does oxygen diffuse?

Answer 47

Down the pressure gradient from alveolus to capillaries until a balance of the partial pressure of oxygen is reached

Question 48

What is the partial pressure of carbon dioxide in the capillaries and alveolus?

Answer 48

High in the capillaries and low in the alveolus

Question 49

Where does carbon dioxide diffuse?

Answer 49

Down the pressure gradient from capillaries to alveolus until a balance of partial pressure of carbon dioxide is reached

Question 50

What are the gradients in external respiration?

Answer 50

Gradient for oxygen to move into capillaries and carbon dioxide to diffuse into the alveolus

Question 51

What are the gradients in internal respiration?

Answer 51

Gradient for oxygen to move into the cells and carbon dioxide to diffuse into the capillaries