Pulmonary Defence Mechanisms Flashcards
Why are the lungs a potential site of immunological vulnerability?
→ 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,
What are some large particulates?
→ Foreign body aspiration (e.g. food, liquid, choke hazards)
What are some fine particulate material?
→ Pollution (<2.5 - 1000 μm)
→ Dust (0.1-1000 μm)
→ Pollen (10 - 100 μm)
What are some microscopic pathogens?
→ Fungal spores (2 - 10 μm)
→ Bacteria (0.5 - 5 μm)
→ Viruses (< 1 μm)
What are some mechanisms that improve immunological defence?
→ 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)
How are nasal hairs helpful?
help filter air and prevent particles from reaching the airways
How are cilia and mucus helpful?
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
How does cystic fibrosis impair mucocilary function?
CFTR mutation ↓ Mucus dehydration + ↓ airway surface fluid ↓ Cilia dysfunction ↓ ↓Mucus clearance
Chronic bronchitis…
Tobacco smoke exposure ↓ Airway inflammation ↓ Goblet cell hyperplasia + cilia damage ↓ Mucus hypersecretion + ↓mucus clearance
How do protective reflexed remove irritants from the airways?
→ 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
Explain how sneezing is initiated…
→ 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
How is coughing triggered?
by stimulation of receptors within the larynx and large airways.
→ coughing can also be initiated voluntarily, and involves bronchoconstriction to further increase expulsion pressure.
Describe laryngeal reflex reflex
→ a short, forcible expiratory effort without a preceding inspiration (differentiating it from coughing)
→ triggered by stimulation of sensory receptors within the vocal folds
What is the role of laryngeal reflex?
→ prevent foreign bodies entering the airways, and to expel phlegm and the upper respiratory tract.
How does branching structure help filter particles?
→ Human airways branch approximately 23 times between the trachea and alveoli so likely blockage
How does air flow type help filter particles?
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.
What do resident immune cells provide?
are present within the tissue structure to provide further defence, coordinate immune responses, and remove deposited particles.
What are the resident immunological defence?
Alveolar macrophages (AM) are the resident phagocytes within the lung and develop from progenitors produced in the bone marrow that migrate to the lung.
Where are AMs found?
found within the airspace
Which materials are not digested by AM?
asbestos fibers, coal/silica dust) cannot be digested
How does airway/lung microbiota help maintain immunological balance?
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.
How does the parasympathetic system modulate mucus secretion and production?
via cholinergic activation of submucosal glands
