Airway resistance,Surfactant

Question 1

List the airways with maximal airway resistance, and those with minimal resistance. Explain your answer

Answer 1

maximal:
- single terminal bronchiole
- bronchi  (small Total Cross Sectional Area)
- pipe smoking (↑ length)
minimal:
- small airways (terminal & respiratory bronchioles) 
- mouth breathing (↓ length)
- tracheostomy (↓ length)

Question 2

the primary factor that determine flow of air……………………………………

Answer 2

The ∆ P (pressure gradient between atmospheric pressure & intralveolar pressure)

Question 3

Explain why a 1 mmHg pressure difference between atmospheric and intraalveolar pressures causes movement of 500mL of air?

Answer 3

because Normally, resistance of airways is very small

Question 4

…………………of air & ………………of airways are constant

Answer 4

Viscosity of air & length

Question 5

…………………… is the primary factor that determine
airway resistance

Answer 5

The 𝑟4(radius of airways)

Question 6

airway resistance Lowest in small airways (terminal & respiratory bronchioles) due to:
This is important to:………………………………………..

Answer 6

1) Parallel arrangement of small airways
2) Very large TCSA
- to give sufficient time for gas exchange

Question 7

Describe the Nervous factors affecting airway resistance

Answer 7

Affect tone of bronchial smooth muscles
Parasympathetic: (the most important) → A.Ch. →
Bronchoconstriction → ↑ resistance. [in relaxed state]

 Sympathetic : (little effect) → Nor.Epi → B2 receptors →
bronchodilation → ↓ resistance. [in stress states]

Question 8

the Local control affecting airway resistance by ……………………..

Answer 8

By alveolar CO2
↓ CO2 in pulmonary capillaries:
bronchoconstriction → ↑ airway resistance & ↓ air flow
↑ CO2 in alveolar air:
bronchodilation → ↓ air way resistance& ↑ air flow

Question 9

Causes of Bronchial asthma

Answer 9

• Allergy
• Excess mucous secretion
• Hyper response of smooth muscles to allergens

Question 10

Pathological actors that increase airway resistance

Answer 10

• Bronchial asthma
• Chronic bronchitis
• Emphysema

Question 11

Causes of Emphysema

Answer 11

Genetic: deficiency of antitrypsin enzyme.
Acquired: Chronic irritation & smoking

Question 12

All COPD are Characterized by

Answer 12

• ↑ air way resistance

- Difficult expiation

Question 13

All COPD are Triggered by

Answer 13

 Smoking
 Polluted air
 Allergens (dust & pollen)

Question 14

Enumerate the factors that keep the small airways opened.

Answer 14

Have no cartilages so Kept open by:

1. Transmural pressure gradient across air ways
2. Elastic lateral traction

Question 15

Define lung compliance, its normal value

Answer 15

= the degree of lung distensibility and the change in lung volume
Normal value:
• Compliance of lungs = 0.2 L / 1 CmH2O
• Compliance of lungs & thoracic wall = 0.1 L / 1 CmH2O

Question 16

Define lung Elastance,

Answer 16

the recoil tendency of lung to its unstretched state

Question 17

Elastic properties of the lung is caused by 2 factors

Answer 17

• Tissue elastic fibers in the lungs

- Surface tension

Question 18

Factors affecting compliance

Answer 18

Factors ↑↑↑ Compliance :
- Old age (↓ elastic recoil)
- Emphysema (↓ elastic fibers due to breakdown of alveoli)
Factors ↓↓↓ Compliance:
- Pulmonary congestion & Edema
- Pneumonectomy (removal of one lung)
- Pulmonary fibrosis
- Respiratory distress

Question 19

Define pulmonary surfactant, its origin

Answer 19

Definition: a surface active agent that ↓ the surface tension of fluid lining the alveoliؤ
Origin: type-II alveolar epithelium (granular pneumocytes)

Question 20

Chemical nature of pulmonary surfactant

Answer 20

• Phospholipid
• Protein
• Calcium

Question 21

Importance & mechanism of action of pulmonary surfactant

Answer 21

Surfactant molecule has:
- Hydrophilic part: facing the alveolar fluid
- Hydrophobic part: facing air
So, it forms a liquid surface facing air → ↓ air-fluid interface →↓surface tension of alveoli 2-10 times → prevents alveoli from collapse

Question 22

Functions of pulmonary surfactant

Answer 22

1) ↓ surface tension of the fluid lining the alveoli
2) ↑ pulmonary compliance & lung expansion
3) ↓ alveolar recoil & prevents their collapse
4) Keep the alveoli dry & prevents pulmonary oedema
5) Stabilization of alveoli

Question 23

Cause of Surfactant deficiency

Infant (newborn) respiratory distress syndrome(IRDS) [Hyaline membrane disease]

Answer 23

↓ surfactant synthesis & maturation → ↑ surface tension

only in premature babies

Question 24

Effects of Surfactant deficiency

Answer 24

↑ surface tension →

• ↓ Compliance
• ↑ Collapse
• ↑ Work of breathing
• Difficult inspiration
• Pulmonary oedema & accumulation of protenacious fluid in the alveoli

Question 25

Factors ↑ alveolar collapse:

Answer 25

1) Tissue elastic forces

2) Surface tension

Question 26

Factors ↑ alveolar opening:

Answer 26

1) Transmural pressure gradient
2) Surfactant
3) Alveolar interdependence

Question 27

Alveolar interdependence

Answer 27

When an alveolus in a group of interconnected alveoli
collapse → stretch of other alveoli → then → ↑ elastic
recoil of the stretched alveoli → opening of the collapsed alveolus