6 – Gas Diffusion

Question 1

Gas exchange steps in respiration:

Answer 1

1. De-O2 blood from pulmonary artery reaches alveoli (low O2, high CO2)
2. CO2 diffuses into alveoli, O2 diffuses into capillary
3. Gas in systemic/tissue capillary travels to tissue where O2 diffuses into the cell and CO2 diffuses into capillary

Question 2

Exercise and gas exchange in respiration:

Answer 2

-tissues PO2 drops and PCO2 increases
*increases P1-P2 to enhance gas exchange

Question 3

What are the different types of pulmonary gas flow?

Answer 3

-bulk flow
-individual movement of gases

Question 4

Bulk pulmonary gas flow:

Answer 4

-different gases move together through conducting airway
-high velocity, turbulent or laminar

Question 5

Individual pulmonary gas flow:

Answer 5

-once gases reach alveoli=decrease in diameter and increase in SA=slow velocity
-at slow velocity=movement of gas occurs individually based on properties of individual gas
*gas diffusion

Question 6

Gases only diffuse from:

Answer 6

-HIGH to LOW partial pressure

Question 7

What is the goal of pulmonary gas diffusion?

Answer 7

-diffuse O2 from alveoli to blood
-diffuse CO2 from blood to alveoli
*must diffuse through tissues and liquid phase

Question 8

What are the layers that gas must diffuse through?

Answer 8

-pulmonary fluid and surfactant
-alveolar epithelium and basement membrane
-interstitial space
-capillary basement membrane and endothelium
-plasma
-RBC

Question 9

How is relative rate of diffusion governed?

Answer 9

-by physically properties
>Henry’s law
>Fick’s law

Question 10

Henry’s law:

Answer 10

-amount of dissolved gas in a solution (blood) is proportional to its partial pressure (alveoli) above the liquid
*bidirectional
*higher pressure=more gas is dissolved

Question 11

Henry’s law equation:

Answer 11

-concentration dissolved gas in liquid=gas constant x partial pressure of gas

Question 12

Alveoli and Henry’s law:

Answer 12

-O2 must move from gas to liquid phase
-CO2 moves from liquid to gas phase

Question 13

Why is 100% oxygen used for animals in respiratory distress?

Answer 13

*Henry’s law
-higher partial pressure of oxygen=increased dissolved oxygen in the blood

Question 14

Fick’s law:

Answer 14

-rate of gas diffusion across a permeable barrier is dependent on 4 factors

Question 15

What are the 4 factors that affect the rate of diffusion across a permeable barrier?

Answer 15

-surface area
-diffusion coefficient (gas specific)
-pressure difference
-barrier thickness

Question 16

Permeable barrier in alveoli consists of:

Answer 16

-tissue and liquid

Question 17

Pressure difference in alveoli:

Answer 17

-P1 (high) and P2 (low) for O2 and CO2 is in opposite space

Question 18

What does increasing the surface area do to diffusion rate?

Answer 18

-increases
*why compliant lung is good and atelectasis is bad

Question 19

What does increasing pressure difference do to diffusion rate?

Answer 19

-increases
*why 100% O2 is good

Question 20

What does increasing barrier thickness do to diffusion rate?

Answer 20

-decreases
*why inflammation/edema is bad

Question 21

Solubility of CO2:

Answer 21

-is 20x more soluble than O2

Question 22

Diffusion between O2 vs. CO2

Answer 22

-despite CO2 having a smaller pressure difference, it has a higher diffusion rate
*allows PCO2 to effectively be diffused but also regulated over a NARROWER RANGE
»tighter control of blood pH

Question 23

Factors that impair diffusion includes factors that:

Answer 23

-affects O2 coming in and CO2 going out
>hypoxemia (low O2)
>hypercapnia (increased CO2, influences pH)

Question 24

What are examples of factors that impair diffusion?

Answer 24

-increased barrier thickness
-decreased SA
-decreased PO2

Question 25

Examples of things that cause increased barrier thickness:

Answer 25

-fibrosis
-inflammation/pneumonia
-edema (interstitial space)

Question 26

Examples of things that cause a decreased SA:

Answer 26

-fibrosis
-low surfactant ->high surface tension (ex. premature animals)
-bronchus obstruction (mucous)
>less air in=don’t expand as much

Question 27

Examples of things that cause a decreased PO2:

Answer 27

-altitude/elevation
-pollution
-re-breathing (anesthesia)
>also increases CO2

Question 28

Effects of altitude:

Answer 28

-decrease in O2 partial pressure with altitude
-low alveolar PO2=decrease pressure difference (P1-P2)=reduce diffusion rate
*grade of hypoxia (low body O2) with different altitudes

Question 29

Alveolar PAO2 is determined by:

Answer 29

-rate of O2 entry into lung (increase PAO2)
-rate of O2 absorption into blood (decrease PAO2)

Question 30

Average alveolar PO2=104mmHg can be achieved with a gas ventilation rate of:

Answer 30

-5L/min at rest
>corresponds to O2 consumption at 250mL O2/min
*to maintain effective P1

Question 31

Exercise and ventilation rate:

Answer 31

=increase in O2
=increase rate of O2 absorption into blood
=decrease alveolar PO2

Question 32

To maintain PO2=104mmHg during exercise:

Answer 32

-need to increase ventilation rate 4-fold (to 20L/min)
>achieve O2 consumption of 1000 mL O2/min

Question 33

Alveolar PO2 can not exceed:

Answer 33

-150mmHg = PO2 in moist tracheal air

Question 34

Alveolar PACO2 is determined by:

Answer 34

-rate of CO2 entering the lung (increase PACO2)
-rate of CO2 leaving the lung (decrease PA CO2)

Question 35

Average alveolar PCO2=40mmHg can be achieved with a CO2 excretion rate of:

Answer 35

-200mL CO2/min at rest
*to maintain effective P2

Question 36

Exercise and CO2 production:

Answer 36

=CO2 production increased (Kreb’s cycle!)
=increase rate of CO2 entering lung/alveolar PCO2

Question 37

To maintain normal PCO2=40mmHg during exercise:

Answer 37

-ventilation rate increases 4x to reach CO2 excretion rate at 800mL/min

Question 38

Alveolar PO2 and alveolar PCO2 and ventilation

Answer 38

-PO2 is proportional to ventilation
-PCO2 is inversely proportional to ventilation