Respiratory Sysytem and Gas Exchange part 2 (slides 50-)

Question 1

So, how much gas is exchanged every minute-Translation-What is “J”?

- Under normal resting conditions:
    - ml of O2 exchanged every minute?
    - ml of CO2 exchanged every minute?

Answer 1

• 250 ml of O2 exchanged every minute
• 200 ml of CO2 exchanged every minute
• They ARE NOT EQUAL!

Question 2

First lesson about gas exchange?

Answer 2

The diffusion of each gas (O2 and CO2) is INDEPENDENT of one another

Question 3

2 factors from alveolar gas exchange equation that depend directly on the structure of the alveolus?

Answer 3

Surface area and diffusion distance (thickness of alveolar barrier)

Question 4

Alveolar gas exchange

-Equation and what is each variable?

Answer 4

J = ((S.A.) x D x (P1-P2))/distance
J: diffusion rate in ml/min
D:diffusion coefficient for each gas
(P1-P2): pressure gradient across alveolar membrane
S.A.:surface area available for diffusion
distance: diffusion distance (thickness of alveolar barrier)
Equation is solved for each gas individually

Question 5

Alveoli

Answer 5

• Thin-walled structures

- In a typical section of lung tissue, most of the tissue sample will be composed of alveoli

Question 6

Alveoli-Separated by?

Answer 6

• Alveoli are separated by interalveolar septa that consist of two simple squamous epithelial layers with an interstitium (non-fenestrated capillaries embedded in an elastic connective tissue) between them
• The structure of the walls enhances diffusion and gas exchange

Question 7

The alveolar epithelium consists of two cell types lining the surface of the capillaries (terminal branches of the pulmonary artery) and the alveolar wall

Answer 7

Type I and type II alveolar cells

Question 8

Type I alveolar cells

Answer 8

Represent about 40% of the alveolar epithelial cell population and cover 90% of the alveolar surface

Question 9

Type II alveolar cells

Answer 9

• Represent about 60% of the alveolar epithelial cell population but cover only 10% of the surface
• Preferentially located at the angles formed by adjacent alveolar septa

Question 10

Type II alveolar cell function?

Answer 10

Produce surfactant

Question 11

Alveolar macrophages (dust cells)

• Part of?
• Where are they located?

Answer 11

• Part of the mononuclear phagocyte system
• Found along the alveolar surface, within the interstitium
• Often seen detached in alveolar lumen of histological sections

Question 12

Alveolar macrophages (dust cells)
   -Function?

Answer 12

• Remove debris that escapes mucus and cilia in the conducting portion of the system
• Many migrate to bronchi and are transported via ciliary action to pharynx to be swallowed or expectorated

Question 13

Alveolar macrophages (dust cells)

• Can be indicative of what disease?
• Why?

Answer 13

• Called HEART FAILURE CELLS IN CONGESTIVE HEART FAILURE
• Left ventricle fails to keep pace with venous return from lungs
• Lungs become congested with blood
• RBCs pass into alveoli and are phagocytosed

Question 14

In the diffusion rate equation (J), S.A. is the surface area available for diffusion
-This means that S.A. corresponds to?

Answer 14

-The number of alveoli in the lungs and the number of open pulmonary capillaries

Question 15

As surface area increases, what happens to J?

Answer 15

As surface area increases, J (diffusion rate) increases

Question 16

Emphysema-Caused by?

Answer 16

-Emphysema is caused by a permanent enlargement of the air spaces distal to the terminal bronchioles due to the progressive and irreversible destruction of elastic tissue of the alveolar walls

Question 17

Emphysema

• Elastic tissue in the interalveolar wall can be destroyed by what enzyme?
• What type of cell releases this enzyme?

Question 18

Emphysema

-Elastase is neutralized by?

Answer 18

-Serum a1-antitrypsin (serum trypsin inhibitor) neutralizes elastase

Question 19

Emphysema

-So what happens in the absence of of a1-antitrypsin?

Answer 19

Neutrophil elastase is free to break down elastin, which contributes to the elasticity of the lungs, resulting in respiratory complications such as emphysema, or COPD

Question 20

Centriacinar emphysema

Answer 20

• Dilated respiratory bronchioles at the apex of the respiratory acinus, surrounded by dilated alveolar ducts and alveoli
• This form of emphysema is found in cigarette smokers

Question 21

Panacinar emphysema

Answer 21

• Thin-walled air spaces of varying sizes are observed in the whole respiratory acinus
• The boundaries of alveoli, alveolar ducts, and respiratory bronchioles are lost by coalescence after destruction of the elastic wall
• This form of emphysema is frequent in individuals with an a1-antitrypsin deficiency

Question 22

Structural landmark of emphysema?

Answer 22

Large air spaces (blebs)

Question 23

What is mainly destroyed in centriacinar emphysema?

Answer 23

The respiratory bronchioles

Question 24

What is mainly destroyed in panacinar emphysema?

Answer 24

Respiratory bronchioles, alveolar ducts, and alveoli

Question 25

Blood-air barrier | -Refers to?

Answer 25

-Refers to the structures that O2 and CO2 must cross during gas exchange

Question 26

Blood-air barrier | -It contains?

Answer 26

- It contains: - Cytoplasm of squamous epithelial cells (type I alveolar cells or pneumocytes) - Fused basal lamina of type I alveolar cells and capillary endothelial cells - Cytoplasm of capillary epithelial cell

Question 27

In the diffusion rate equation, what happens to J when distance is increased?

Answer 27

J (diffusion rate) decreases as distance (thickness of alveolar barrier) increases

Question 28

Distance includes?

Answer 28

- Fluid layer - Alveolar epithelium - Interstitial space - Blood vessel wall

Question 29

Pathology of Pulmonary interstitial Fibrosis

Answer 29

The deposition of collagen within the interstitial spaces increases the diffusion distance and decreases the diffusion of the gases across the barrier

Question 30

Acute Respiratory Distress Syndrome | -A form of?

Answer 30

-A form of pulmonary edema that causes acute respiratory failure

Question 31

Acute Respiratory Distress Syndrome (ARDS) | -Results from?

Answer 31

- Results from increased permeability of the alveolocapillary membrane - Results from an increase in the hydrostatic pressure in the alveolar capillaries (cardiogenic) or damage to the alveolar epithelial lining caused by bacterial endotoxins or trauma (noncardiogenic)

Question 32

Acute Respiratory Distress Syndrome (ARDS) | -What happens as a result?

Answer 32

- **Fluid accumulates in the lung interstitium**, alveolar spaces, and small airways, causing the lung to stiffen - This stiffening impairs ventilation, prohibiting adequate oxygenation of pulmonary capillary blood

Question 33

ARDS | -Severe ARDS can cause?

Answer 33

Severe ARDS can cause intractable and fatal hypoxemia, but patients who recover may have little or no permanent lung damage

Question 34

D: Diffusion coefficient for each gas | -Depends on?

Answer 34

- The solubility of the gas in water (in your body) - CO2 is much more soluble than O2 - The molecular weight of the gas - CO2 weighs more than O2

Question 35

Pressure gradient | -Which gas has the larger pressure gradient-O2 or CO2?

Answer 35

O2 has the larger pressure gradient

Question 36

DL O2 | -Normal value at rest??

Answer 36

- Diffusion capacity of the lung for oxygen - Normal value at rest = 21 ml O2/min/mmHg - mmHg: avg gradient along alveolar capillary

Question 37

Measuring the DL O2 - ***What gas is used? Why?*** - ***What is the correction factor?***

Answer 37

- Carbon monoxide is used to measure the DL O2 - Used because it binds to Hb so avidly that it doesn't dissolve in the plasma - Correction factor: DL O2 = 1.23 x DL CO

Question 38

Describe the diffusion capacity of the lung for CO2 and O2

Answer 38

How much of each gas crosses in 1 minute for every 1 mmHg gradient

Question 39

Describe how we measure the diffusion capacity for Oxygen and be able to calculate DL O2

Answer 39

- Measured using carbon dioxide - To convert from DL CO to DL O2, multiply by 1.23 - Calculates to about 21 ml O2/min/mmHg

Question 40

Pneumocyte type I

Answer 40

Squamous alveolar epithelium

Question 41

Pneumocyte type II

Answer 41

Surfactant secreting cells

Question 42

***Why is surfactant important?***

Answer 42

- Surfactant changes the surface tension (T) - It reduces T in the smallest alveoli more than in larger alveoli to account for the change in the radius between the two different sized alveoli