Lecture 8: Control of the pulmonary airways

Question 1

Describe features of the airways important to controlling the flow of air;

Answer 1

Bronchioles have smooth muscle which allow them to constrict and dilate (changes resistance to airflow)

Cartilage allows bending of the airways without kinking

Question 2

Describe the relationship of resistance and cross sectional area;

Answer 2

Highest resistance is in the trachea and this funnels outwards (upside down funnel) such that;

The alveoli have the lowest resistance because of the highest cross sectional area

Question 3

Describe the relationship of airflow and cross sectional area;

Answer 3

Airflow is greatest in the trachea (Fast turbulent) and least in the alveoli (Slow laminar) (funnel like)

Question 4

What factors influence airway flow?

Answer 4

1) Physical factors affecting airflow
2) Chemical influences on airways
3) Autonomic control of airways

Question 5

Describe what parts of the airways contribute to airway resistance to flow;

Answer 5

Upper airways 50-70%
Lower airways: (30-50%)
- Trachea 40%
- Bronchi 40%
- Bronchioles 20%

Question 6

What physical factors contribute to airflow control;

Answer 6

As lung volume increases, airway diameter increases and airway resistance decreases

Radial traction influences this

Question 7

What are the chemical influences on airways?

Answer 7

Nervous -> Cholinergic (Constrict) + Adernergic (Dilate)

Neurohormonal -> Ach (constrict) + Norepinephrine (Dilate)

Chemical -> (Constrictors: Histamine, SRS-A, Prostaglandins) (Dilators: CO2 and Prostaglandins)

Physical -> Constrictors (Smoke, dust) (Dilators; not known)

Question 8

What is SRS-A?

Answer 8

Slowly Reacting Substance of Analphylaxis

Question 9

Describe the homeostatic reflex of airway diam and resistance;

Answer 9

Sensory receptors; (baro, stretch, irritant)
Afferents
CNS
Efferent motor
Efferent or target organ
- Heart
- arteriole
- bronchiole

Question 10

Describe the ANS control of airways in relation to the cough reflex;

Answer 10

Irritant receptors (sensory receptors)

Medulla oblongata

Bonchioconstriction (Ach) (coughing) (effectors)

Question 11

Describe the ANS hering-breuer inflation reflex;

Answer 11

Lung stretch receptors / mechanoreceptors (sensory)

Medulla oblongata

Bronchioles (Bronchidilate) (symp efferent)

Question 12

Whats a measure of lung health?

Answer 12

FEV1/FVC

• Forced expiratory volume 1 sec
• Forced vital capacity

~ 80 %

Question 13

What is restrictive lung disease?

Answer 13

Restricts lung expansion on inspiration, resulting in decreased lung volume, increased work of breathing, inadequate ventilation

Question 14

What happens to FEV1/FVC in restrictive lung disease?

Answer 14

FEV1 and FVC are both reduced

The decline in FVC is > FEV1 resulting in a higher than 80% ratio (FEV1/FVC)

Question 15

What is obstructive lung disease?

Answer 15

Obstruction within the airways impedes exhalation

• Narrowing due to excessive constriction of airway smooth muscle
• inflammation and easily collapsible airways
• physical obstruction i.e mucus

i.e asthma, bronchiectasis, COPD, CF

Question 16

What happens to FEV1/FVC in obstructive lung disease?

Answer 16

• Increased airway resistance
• FEV1 and FVC are both reduced
• But FEV1 is reduced more than FVC
• FEV1/FVC ratio is reduced relative to normal

(Takes much longer to expire b/c resistance)

Question 17

What is the regional difference in ventilation within the lung?

Answer 17

Increased air / ventilation at base of lung compared to apex because of gravity…..

Alveoli at top of lung are larger diam therefore limited ability to inflate, and pleural pressure is greater at the top of the lung vs base therefore this limits expansion too