Lecture 18: O2 and CO2 Exchange

Question 1

What is the respiratory minute volume?

Answer 1

The amount of air we breath in and out per unit time, the rate of air inhaled and exhaled

Question 2

What is the equation for respiratory minute volume?

What are the units for respiratory minute volume?

Answer 2

VE = VT x f

L/min

Question 3

What does VT stand for?
What does this mean?
What are the units?

Answer 3

tidal volume
the amount of air inhaled per breath (ie. breathing strength)
L/breath

Question 4

What does f stand for?
What does this mean?
What are the units?

Answer 4

respiratory rate
breathing speed
breaths/min

Question 5

What is dead space?

Answer 5

the volume of inhaled air that remains in the bronchial tree that does not reach the alveoli

Question 6

What is the alveolar ventilation?

What are the units?

Answer 6

the amount of air that reaches the alveoli

L/min

Question 7

What is the equation for alveolar ventilation?

Answer 7

VA = (VT - VD) x f

Question 8

Which is lower, respiratory minute volume or alveolar ventilation?

Answer 8

alveolar ventilation

Question 9

What is Dalton’s Law?

Answer 9

The pressure of a mixed gases is the sum total of the pressure of each individual gas

Question 10

Describe the composition of the dry inhaled air in order

Answer 10

Majority is nitrogen
Oxygen
water vapor
CO2

Question 11

How has the composition of air changed between the dry inhaled air and the saturated air in the alveolar sac?

Answer 11

The nitrogen has dropped slightly
The oxygen has dropped slightly
The carbon dioxide has increased a lot but still less than O2
The water vapour has increased a lot but still less that O2

Question 12

Why does the O2 level drop in the alveolar air?

Answer 12

Because it is lost to the bloodstream

Question 13

Why does the CO2 level increase in the alveolar air?

Answer 13

Because it enters from the bloodstream

Question 14

How has the composition of air changed between the saturated air in the alveolar sac and the saturated exhaled air?

Answer 14

The nitrogen has dropped slightly
The O2 has increased
The CO2 has decreased
The water vapour has remained the same

Question 15

Why does the O2 level increase in the exhaled air compared to the alveolar air and how does this compare to the inhaled air?

Answer 15

• because it mixes with the oxygen that remains in the dead space that never made it to the alveoli
• it is decreased compared to the inhaled air

Question 16

What three factors determine the rate of diffusion across the blood barrier?

Answer 16

• surface area of the membrane
• thickness of the membranes
• pressure difference between the two sides

Question 17

How does the surface area affect the rate of diffusion?

Answer 17

increased surface area increases the rate of diffusion

Question 18

What is a condition that shows that surface area affects the rate of diffusion? How does it affect the rate of diffusion and why?

Answer 18

emphysema is a disease which causes dilation of the alveolar spaces and alveolar walls
there is a reduction in the surface area which means there is less contact between the air and the capillaries, so O2 exchange is greatly reduced

Question 19

How does the thickness of the membrane affect the rate of diffusion?
Why?

Answer 19

thicker membrane decreases the rate of diffusion because there is a greater distance to travel

Question 20

What is a condition that shows that membrane thickness the rate of diffusion? How does it affect the rate of diffusion?

Answer 20

pulmonary fibrosis which thickens and scars the alveolar membranes
this decreases the rate of diffusion

Question 21

What three things determines the pressure difference between the capillaries and alveolar sacs?

Answer 21

1. atmospheric oxygen
2. alveolar ventilation
3. blood oxygen

Question 22

How does atmospheric oxygen affect the pressure difference?

Answer 22

Increased atmospheric O2 increases the alveolar oxygen

Question 23

What affects the alveolar ventilation (which then affects the pressure difference)?

Answer 23

tidal volume and respiratory rate (if these increased, alveolar ventilation increases as VD stays pretty much constant)

Question 24

What factor affects the O2 in the blood (which then affects the pressure difference)?

Answer 24

The exercise level

Question 25

Describe the O2 level in the blood when at rest and how this affects the amount in the alveoli

Answer 25

there is reduced O2 consumption so there is increased O2 in the venous return so there is less of a need to transfer O2 to the blood from the alveoli

Question 26

Describe the O2 level in the blood when exercising and how this affects the amount in the alveoli

Answer 26

there is increased O2 consumption so there is less O2 in the venous blood and therefore more O2 is pulled from the alveoli into the blood

Question 27

The process of diffusion and determining factors also work for CO2
TRUE OR FLASE?

Answer 27

true

Question 28

exchange stop when the _________ is the same

Answer 28

pressure

Question 29

Which is lower, alveolar ventilation or respiratory minute volume and why?

Answer 29

alveolar ventilation is lower due to dead space