Intro to Respiratory Physiology - Trachte

Question 1

What are the four basic components of Respiratory Physiology?

Answer 1

1. Ventilation
2. Perfusion
3. Diffusion
4. Exchange

Question 2

How do gasses move across the blood-gas interface?

Answer 2

Diffusion

(high pressure → low pressure)

Question 3

What is the driving force of oxygen in diffusion?

Answer 3

• Partial pressure air > Partial pressure blood
  
  • Air = 150 mmHg (humidified)
  • Venous blood = 40 mmHg
  • Moves from AIR → BLOOD via diffusion

Question 4

What is the driving force of carbon dioxide in diffusion?

Answer 4

• Partial pressure blood > Partial pressure air
  
  • Venous Blood = 46 mmHg
  • Air = 0 mmHg
  • Moves from BLOOD → AIR by diffusion

Question 5

Gases move across the capillary/alveolar barrier depending on what?

Answer 5

• Cross-sectional area of the barrier (50-100 m²)
  
  • tons of blood vessels surrounding alveoli
  • greater surface area → greater potential for diffusion
  • more vasculature → more efficient exchange
• Inversely proportional to the thickness of barrier
  
  • thicker barrier → less diffusion
  • thinner barrier → more permeable
    
    • CO₂ is more permeable than O₂

Question 6

What are conducting airways?

Answer 6

• Branched tubes that conduct air but are not involved in gas exchange
• They comprise anatomic “dead space”
  
  • have gas concentrations similar to atmosphere, except that air is humidified

Question 7

What are the conducting airways composed of?

Answer 7

• Trachea
• Right & Left bronchi
• Lobar bronchi
• Segmental bronchi
• Eventually → Terminal bronchioles
  
  • smallest airways without alveoli

Question 8

What is the typical volume of air that the conducting airways hold?

Answer 8

150 mL

Question 9

What is the volume of a normal breath?

Answer 9

500 mL

Question 10

Can you think of clinical examples that are the equivalent of a longer neck?

Answer 10

Intubated patient

tube → increases dead space

Question 11

What is the respiratory zone?

Answer 11

• Acinus
  
  • terminal bronchioles divide into → respiratory bronchioles
    
    • occasional alveoli
  • respiratory bronchioles lead to → alveolar ducts
    
    • completely lined with alveoli

Question 12

What is airflow initiated by?

Answer 12

• Expansion of thoracic cavity
  
  • Diaphragm contracts (moves downward)
  • Intercostals contract (raises ribs)

Question 13

Where does dust settle in the respiratory tract if inhaled?

Answer 13

Terminal bronchioles

(not alveoli)

Question 14

Why is the lung so easy to expand?

Answer 14

Very compliant!

• Lungs are balanced between chest wall
  
  • helps with compliance to volume change
• Compliance = change in volume/change in pressure)

Question 15

How much of the body’s total metabolic work is spent on breathing?

Answer 15

15%

(this is why COPD patients get so tired)

Question 16

What is the path of blood flow in the lungs?

Answer 16

• Pulmonary artery (O₂ poor) →
• Capillaries →
• Pulmonary Vein (O₂ rich)

Question 17

Because the capillaries in the lungs have extremely thin walls, they are at increased susceptibility to damage from what processes?

Answer 17

• Increasing capillary pressure
  
  • e.g. pulmonary HTN
• Increasing alveolar pressure
  
  • e.g. tension pneumothorax

***The capillaries have the same amount of flow through them as the pulmonary artery/vein, but with much less resistance!

Question 18

How long do RBCs spend in the pulmonary capillaries?

Answer 18

less than a second

Question 19

Alveoli are 500 million bubbles and surface tension should make them want to collapse when they are small, but a really important mechanism keeps them from doing so. What is it?

Answer 19

Lung surfactant

• reduces surface tension and prevents alveolar collapse
  
  • Surfactant = nonpolar tail + polar head
    
    • prevents water molecules from attracting each other → decreases Tension
  • develops at 7 months gestation

Question 20

What are the three mechanisms to eliminate unwanted inhaled particles?

Answer 20

1. Can be filtered (nose)
2. Can be moved toward the mouth by a mucous-ciliary elevator (inhibited by cigarrete smoke)
3. Can be engulfed by macrophages (typically in alveoli)