Lecture 37 - Mechanics of Ventilation

Question 1

What is the primary function of the respiratory system?

Answer 1

o Supply tissues with oxygen
o Remove CO2 from tissues

Question 2

What is the oxygen cascade?

Answer 2

o Getting O2 from the environment
o To the blood
o To the tissue
o To the mitochondria

Question 3

What is the difference between conductive zones and respiratory zones?

Answer 3

Conductive zones include the larger airways responsible for guiding air into lungs and conditioning it, whereas the respiratory zone consists of the smaller airways and alveoli where gas exchange takes place.

Question 4

What is the conductive zone?

Answer 4

Also known as the anatomical dead space, air in this space does not undergo gas exchange but does undergo conditioning

Question 5

Key structures found in conductive zone

Answer 5

Nasal cavity, pharynx, larynx, trachea, bronchi

Question 6

What is the respiratory zone?

Answer 6

Where gas exchange occurs, oxygen is taken up by the blood and CO2 is released into the air.

Question 7

Key structures of the respiratory zone

Answer 7

Bronchioles, alveolar ducts, alveoli, respiratory membrane.

Question 8

Architecture of human lung (big to small)

Answer 8

o Conducting zone: Trachea – bronchi – bronchioles – terminal bronchioles
o Respiratory zone: respiratory bronchioles – alveolar ducts – alveolar sacs

Question 9

Cell types found in alveolus

Answer 9

o Type I alveolar cells – squamous pulmonary epithelial
o Type II alveolar cells – septal
o Macrophages

Question 10

Volumes of respiratory

Answer 10

o Tidal volume = 500mL
o Total ventilation = 6000mL
o Respiratory frequency = 12/min
o Anatomical dead space = 150mL
o Alveolar gas = 3000mL
o Alveolar ventilation = 4200mL
o Pulmonary capillary blood (in) = 70mL
o Pulmonary blood flow (out) = 4200mL/min

Question 11

What are the muscles of inspiration?

Answer 11

o Diaphragm
 2 hemi-diaphragms
 Innervated by phrenic nerve
 Origins C3-5
o External intercostal
 Innervated by intercostal nerves
 Origins T1-T11
o Accessory muscles
 Sternocleidomastoid
Scalenes

Question 12

Ventilation at rest

Answer 12

Inspiration = active
Expiration = passive

Question 13

Ventilation under stress

Answer 13

o Inspiration = active
o Expiration = active

Question 14

Active expiration muscles:

Answer 14

o Abdominal muscles
o Internal intercostals

Question 15

Rest expiration muscles

Answer 15

o Expiration passive
o Relaxation of diaphragm
o Passive recoil of lungs

Question 16

What is the role of upper airway muscles in ventilation and airway resistance?

Answer 16

o Help maintain airway patency (openness)
o Influence volume and speed of airflow
o Speech and phonation
o Swallowing and protection
o Exercise and breathing patterns

Question 17

Describe and explain the pressure changes during the different phases of breathing

Answer 17

o Inhalation involves a decrease in intra-thoracic pressure as the volume inceases, allowing air to flow into lungs
o Exhalation involves an increase in intra-thoracic pressure as the volume decreases, facilitating air movements out of the lungs.

Question 18

Site of airway resistance

Answer 18

Bronchial smooth muscles

Question 19

Velocity of flow is inversely proportional to?

Answer 19

Cross sectional area

Question 20

Control of airway resistance

Answer 20

o Contraction of bronchial smooth muscles
o Reduce diameter of airway
o Increase resistance

Question 21

How are bronchial smooth muscles controlled?

Answer 21

o Contraction - cholinergic acting on muscarinic nicotinic receptors) + noncholinergic parasympathetic nerves
o Relaxation – circulating catecholamines acting of B2-adrenergic receptors

Question 22

What is conductance

Answer 22

o Reciprocal of airway resistance
o Lung volume is inversely proportional to airway resistance

Question 23

How is compliance measured?

Answer 23

Change in volume/change in pressure

Question 24

What happens when compliance is decreased?

Answer 24

o Increase fibrosis
o Increase surface tension
o Alveolar oedema
o Ageing
o Emphysema
o Elastin and collagen aids elastic recoil

Question 25

Effect of surfactants

Answer 25

o Increase compliance
o Increase stability

Question 26

Type II alveolar cells extrude surfactants

Answer 26

o Rapid turnover
o Phospholipid DPPC
o Synthesised in lungs

Question 27

What is the equation involving pressure, surface tension and radius?

Answer 27

P = 4T/r

Question 28

Interdependence of alveoli and lung parenchyma

Answer 28

o Adjacent alveoli – lung parenchyma provide radial traction
o Elastic properties of the lung