Pulmonary Defence Mechanisms

Question 1

Why are the lungs a potential site of immunological vulnerability?

Answer 1

→ Fast movement of air from atmosphere to respiratory surfaces - places limits on filtering/barrier structures possible
→ Efficient gas exchange - requires a thin membrane innervation by blood vessels, and a warm,

Question 2

What are some large particulates?

Answer 2

→ Foreign body aspiration (e.g. food, liquid, choke hazards)

Question 3

What are some fine particulate material?

Answer 3

→ Pollution (<2.5 - 1000 μm)
→ Dust (0.1-1000 μm)
→ Pollen (10 - 100 μm)

Question 4

What are some microscopic pathogens?

Answer 4

→ Fungal spores (2 - 10 μm)
→ Bacteria (0.5 - 5 μm)
→ Viruses (< 1 μm)

Question 5

What are some mechanisms that improve immunological defence?

Answer 5

→ Physical obstructions:
Macro = nasal hairs, turbinates, branching airways.
Micro = cilia, mucous.
→ Protective reflexes: coughing, sneezing, expiratory reflex
→ Immunological defence system:
Lung resident immune cells (e.g. alveolar macrophages)
Structural cells (epithelial cells)/innate immunity
Antimicrobial proteins
→ Biological symbiosis? (commensals/microbiota)

Question 6

How are nasal hairs helpful?

Answer 6

help filter air and prevent particles from reaching the airways

Question 7

How are cilia and mucus helpful?

Answer 7

trap and remove microorganisms and particles
→ Pushed in one direction- reverse stroke, they pivot and curl up so overall diameter is reduced so when it moves backward it is not within the gel

Question 8

How does cystic fibrosis impair mucocilary function?

Answer 8

CFTR mutation
↓
Mucus dehydration + ↓ airway surface fluid
 ↓
Cilia dysfunction
↓
↓Mucus clearance

Question 9

Chronic bronchitis…

Answer 9

Tobacco smoke exposure
↓
Airway inflammation
↓
Goblet cell hyperplasia + cilia damage
↓
Mucus hypersecretion + ↓mucus clearance

Question 10

How do protective reflexed remove irritants from the airways?

Answer 10

→ activation of afferent sensory neurons
→ transmit the impulse to breathing centres within the brain (i.e. the medulla, located within the brainstem)
→ Efferent signals are then transmitted to specific respiratory muscles,
the glottis and airways to initiate a coordinated respiratory effort which rapidly expels air from the nasal cavity/airways/lungs

Question 11

Explain how sneezing is initiated…

Answer 11

→ by stimulation of sensory receptors within the nasal cavity
→ involves a deep inspiration phase
→ a compression phase -(during which the glottis is closed, leading to pressure build-up)
→ a final expiration phase in which air is expelled

Question 12

How is coughing triggered?

Answer 12

by stimulation of receptors within the larynx and large airways.
→ coughing can also be initiated voluntarily, and involves bronchoconstriction to further increase expulsion pressure.

Question 13

Describe laryngeal reflex reflex

Answer 13

→ a short, forcible expiratory effort without a preceding inspiration (differentiating it from coughing)
→ triggered by stimulation of sensory receptors within the vocal folds

Question 14

What is the role of laryngeal reflex?

Answer 14

→ prevent foreign bodies entering the airways, and to expel phlegm and the upper respiratory tract.

Question 15

How does branching structure help filter particles?

Answer 15

→ Human airways branch approximately 23 times between the trachea and alveoli so likely blockage

Question 16

How does air flow type help filter particles?

Answer 16

When inhaled air reaches an airway branching site, airflow changes from laminar to semi-turbulent flow pattern, increasing particle deposition as more particles come into contact with the mucus-lined airway wall.

Question 17

What do resident immune cells provide?

Answer 17

are present within the tissue structure to provide further defence, coordinate immune responses, and remove deposited particles.

Question 18

What are the resident immunological defence?

Answer 18

Alveolar macrophages (AM) are the resident phagocytes within the lung and develop from progenitors produced in the bone marrow that migrate to the lung.

Question 19

Where are AMs found?

Answer 19

found within the airspace

Question 20

Which materials are not digested by AM?

Answer 20

asbestos fibers, coal/silica dust) cannot be digested

Question 21

How does airway/lung microbiota help maintain immunological balance?

Answer 21

The mucosal surfaces of the respiratory system are not sterile (even in healthy individuals) – they are colonised by huge numbers of commensal bacteria
→ important roles in resisting infection by other pathogens and the development/modulation of a healthy immune system. The populations of organisms colonising airways in health vs. disease appear to vary, however whether this change contributes to the pathology, or merely results from it, is still under debate.

Question 22

How does the parasympathetic system modulate mucus secretion and production?

Answer 22

via cholinergic activation of submucosal glands