Pulmonary Defence Mechanisms Flashcards
Describe why the lungs are immunologically vulnerable
Fast movement of air from the 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 moist environment in which microorganisms also thrive in
State what the air contains and categorise these into sizes of particulates
- Large particulates -
Foreign body aspiration e.g. food, liquid, other choke hazards - Fine particulates -
Pollution
Dust
Pollen
Smog
Tobacco smoke
Mould spores - Microscopic pathogens -
Fungal spores
Bacteria
Viruses
State some pathologies that can result in the lungs and what causes them
- Tuberculosis from bacterial infection
- Pneumonia from viral infection
- Aspergillosis from fungal infection
- Bronchitis from inflammation of the bronchi
- Whooping cough
- Measles
- Asthma from inhalation of allergens
- Lung cancer from inhalation of carcinogenic particles
- Occupational lung disease can be caused by coal miners dust
- Allergic rhinitis
- Emphysema - can be caused by smoking
State the four main categories of defence the lungs have
- Physical obstructions
- Protective reflexes
- Immunological defence mechanism
- Biological symbiosis
State in more detail examples of each of these types of defences
- Physical obstructions -
Macro - nasal hairs, turbinates (ridge structures in the nose), branching airways
Micro - cilia (waft mucus out of the airways and into trachea to be swallowed and microorganisms killed), mucous (traps microorganisms) - Protective reflexes -
Coughing
Sneezing
Expiratory reflex - Immunological defence mechanism -
Lung resident immune cells like alveolar macrophages
Structural cells like epithelial cells/innate immunity
Antimicrobial proteins - Biological symbiosis -
Commensals
Microbiota
Describe the structure of the ciliated tissue found in the airways
- There is a gel layer which forms a mucus blanket over the tissue (green layer)
- There are then goblet cells which are ciliated - goblet cells produce the mucous
- There are invaginations of the basement membrane at intervals along the tissue which form submucosal glands in the lamina propria
Describe how the cilia move to waft mucus
- Called the mucociliary escalator constantly pushes mucus from the airways into the trachea where it can then be expelled into the GI tract
- When the cilia move backwards (reverse stroke) they curl up so the depth to which they penetrate the mucus decreases - it is in the periciliary layer not the mucus gel layer so the mucus doesn’t move
- When the cilia moves forwards (forward stroke) they fully extend into the mucus layer so the mucus is moved along with the cilia
State and describe 2 conditions that occur due to impairment of mucocillary function and what the symptoms produced can be
- Cystic fibrosis -
When there is a mutation in the CFTR gene there is mucus dehydration meaning that there is decreased airway surface fluid
There is therefore cilia dysfunction which means there is decreased mucus clearance - Chronic bronchitis -
When there is tobacco smoke exposure it causes airway inflammation
This then leads to goblet cell hyperplasia and cilia damage
It then causes mucus hypersecretion which then decreases mucus clearance - Effects of this lack of function -
Increased frequency of respiratory infections
Productive cough
Airway dysfunction and obstruction
Describe protective reflexes that can expel irritant particles from the airway
- Coughing
- Sneezing
- Laryngeal expiratory reflex
- There is stimulation of mechanoreceptors or chemoreceptors in the throat, respiratory passages or stretch receptors in lungs
- Afferent impulses are sent to the central nervous system e.g. medulla
- Efferent impulses via parasympathetic and motor nerves sent to necessary muscles
- Sneezing -
- Initiated by stimulation of sensory receptors within the nasal cavity
- Involves a deep inspiration phase, a compression phase during which the glottis is closed to increase pressure, and then an expiration phase where air is expelled
- Coughing -
- Involves these three phases but is triggered by stimulation of receptors in the larynx and large airway
- Coughing can be initiated voluntarily unlike sneezing
- It involves bronchoconstriction to increase expulsion pressure
- Laryngeal reflex -
- Short, forcible expiratory effort without preceding inspiration
- It is triggered by stimulation of sensory receptors within the vocal folds
- This prevents foreign bodies entering the airways and to expel phlegm from the upper respiratory tract
Describe how branching helps to filter particles
The branching means that air naturally becomes turbulent when the diameter becomes smaller or when the branching occurs
When the air is turbulent it travels in multiple directions and so is more likely to come into contact with mucus producing cells and cilia so more microorganisms are removed
Describe how resident immune cells remove particles
- Microbe adheres to a phagocyte
- Phagocyte forms pseudopods that engulf the particle
- Phagocyte forms a vesicle called a phagosome containing the particle
- Phagocytic vesicle is fused with a lysosome to form a phagolysosome
- Microbe in vesicle is killed and digested by lysosomal enzymes in the phagolysosome leaving a residual body
- Indigestible and residual material is removed by exocytosis
- The phagocyte can also present antigens on its surface to recruit immune cells to that area
NOTE - phagocytes cannot digest everything so silicone, asbestos and coal miners dust etc are unable to removed in this way and can lead to silicosis, asbestosis and pneumoconiosis
Describe how structural cells can detect pathogens and alert immune cells
- Pathogen recognition receptors (PRRs) on epithelial cells can bind to PAMPs (pathogen associated molecular patterns) or conserved aspects of pathogens like polysaccharides of bacterial cell walls and viral DNA
- This then causes cytokines to be released by the epithelial cells
- These cytokines then cause white blood cells to migrate to the area and become activated
State why we believe airways/lung microbiota help to maintain health and why evidence is not yet solid
Studies have shown that the population sizes of different types of bacteria differ between those with different conditions
