Gas Diffusion

Question 1

Gas exchange in respiration steps

Answer 1

1.Deoxygenated blood from pulmonary artery reaches alveoli (low O2 and high CO2)
2. CO2 diffuses into alveoli and 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

Gas pressure changes during exercise

Answer 2

-during exercise, tissue O2 pressure levels drop and CO2 pressure levels increase
-the increase in the pressure difference (P1-P2) will result in enhanced gas exchange

Question 3

Pulmonary gas flow in conducting zone

Answer 3

Different gas moves together through the conducting airway
- bulk flow, high velocity, turbulent or laminar

Question 4

Pulmonary gas flow in alveoli

Answer 4

Once gases reach the alveoli, there is a decrease in diameter and an increase in surface area. This results in flow decreasing its velocity
-At a slow velocity, gas movement occurs individually through diffusion based on properties of each gas
-Gases diffuse from high partial pressure to low partial pressure

Question 5

Goals of pulmonary gas diffusion

Answer 5

1.to diffuse O2 from alveoli into blood
2. to diffuse CO2 from blood to alveoli

Question 6

Pulmonary gas diffusion layers

Answer 6

-must diffuse through tissues and liquid phase

Layers:
1.pulmonary fluid and surfactant
2.alveolar epithelium and basement membrane
3.interstitial space (fluid can build up here making gas movement more difficult)
4.capillary basement membrane and endothelium
5.plasma
6.RBC

Question 7

What laws impact rate of diffusion of gases?

Answer 7

-Henry’s Law
-Fick’s Law

Question 8

Henry’s Law equation

Answer 8

Concentration dissolved gas in liquid (C)= gas constant (K) X partial pressure of gas (P)

Question 9

Henry’s Law

Answer 9

-the amount of dissolved gas in a solution is proportional to its partial pressure above the liquid
Bidirectional

Question 10

Henry’s law in alveoli

Answer 10

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

*if you double the partial pressure, then you double the concentration of O2 dissolved in liquid

Question 11

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

Answer 11

-because of Henry’s Law
-higher partial pressure results in an increase in dissolved oxygen in the blood

Question 12

Fick’s Law Equation

Answer 12

Rate of gas exchange= surface area (A) x diffusion coefficient (D) X ((Pressure difference Phigh-Plow)/Barrier thickness (T))

Question 13

Fick’s Law

Answer 13

-the rate of gas diffusion across a permeable barrier is dependent on surface area, diffusion coefficient, pressure difference, and barrier thickness

Question 14

What happens to rate of gas diffusion when surface area increased?

Answer 14

-An increase in diffusion

*Reason why compliant lung is good and atelectasis is bad**

Question 15

What happens when pressure difference has increased?

Answer 15

Increase in diffusion

Reason why 100% O2 is good

Question 16

What happens when barrier thickness is increased?

Answer 16

-diffusion is decreased

Reason why inflammation/edema is bad

Question 17

Diffusion coefficient of CO2 compared with O2

Answer 17

CO2 is 20x more soluble than O2

Question 18

Pressure gradients for O2 compared with CO2

Answer 18

-O2: higher pressure inside alveoli, lower pressure outside

-CO2: higher pressure outside alveoli, lower pressure inside
**CO2 has smaller gradient than O2 gradient

Question 19

Diffusion rate of CO2 compared with O2

Answer 19

CO2 has a slightly higher diffusion rate than O2 overall
-Even though CO2 has a smaller pressure difference

CO2 being higher allows for effective diffusion but is also regulated over a narrower range (because tighter control needed due to its effect on blood pH)

Question 20

Factors that impair diffusion

Answer 20

-increased barrier thickness
-decreased surface area
-decreased O2 pressure in the alveoli

Question 21

What occurs when O2 coming in is affected?

Answer 21

-hypoxemia

Question 22

What occurs when CO2 going out is affected?

Answer 22

-hypercapnia

Question 23

What can cause increased barrier thickness?

Answer 23

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

Question 24

What can cause decreased surface area?

Answer 24

-fibrosis
-low surfactant (high surface tension)
-bronchus obstruction (mucous)

Question 25

What can cause decreased O2 pressure inside the alveoli?

Answer 25

-altitude/elevation
-pollution
-re-breathing (anesthesia)

Question 26

Effect of altitude

Answer 26

-decrease O2 partial pressure with altitude
-low alveolar O2 pressure results in decreased pressure difference and therefore a reduced diffusion rate

Question 27

What determines O2 alveolar pressure?

Answer 27

1.rate of O2 entry into lung (increase O2 alveolar pressure)
2.Rate of O2 absorption into blood (decrease CO2 alveolar pressure)

Question 28

Max alveolar O2 pressure

Answer 28

-it cannot exceed 150 mm Hg (in moist tracheal air)

Question 29

Alveolar O2 pressure and Gas ventilation at rest

Answer 29

-Avg alveolar O2 pressure= 104 mm Hg
-achieved with gas ventilation rate of 5 L/min and O2 consumption of 250 ml O2/min

Question 30

Alveolar O2 pressure and gas ventilation during exercise

Answer 30

-during exercise, there is an increase in O2 demand and therefore an increase in rate of O2 absorption into blood which decreases alveolar O2 pressure

-ventilation rate must increase 4-fold to 20L/min to achieve O2 consumption of 1000ml O2/min

Question 31

What determines CO2 alveolar pressure?

Answer 31

1.rate of CO2 entering the lung (increase CO2 alveolar pressure)
2.rate of CO2 leaving the lung (decrease CO2 alveolar pressure)

Question 32

Average alveolar CO2 pressure

Answer 32

40 mm Hg

Question 33

Alveolar CO2 pressure and gas ventilation at rest

Answer 33

-Avg alveolar CO2 pressure= 40 mm Hg
-CO2 excretion rate at 200ml CO2/min

Question 34

Alveolar CO2 pressure and gas ventilation during exercise

Answer 34

-during exercise, an increase in CO2 production occurs (Kreb’s cycle) resulting in an increased rate of CO2 entering the lung/alveolar CO2 pressure
-ventilation rate increases 4x to reach CO2 excretion rate at 800 ml/min in order to maintain average 40mm Hg

Question 35

Proportionality of alveolar pressure for CO2 and O2

Answer 35

-Alveolar pressure of O2 is proportional to ventilation
-Alveolar pressure of CO2 is inversely proportional to ventilation