Pulmonary defence mechanisms Flashcards
How much oxygen do we consume per day?
How much air do we breathe in from the atmosphere?
- Humans consume ≈ 500L of oxygen/day
2. Inhalation of 8000 L of air/day.
What are the two requirements for this huge volume of air to be moved to respiratory surfaces?
- 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, moist environment (in which microorganisms also thrive).
The air is not sterile, it, therefore, can contain harmful substances, gives some examples
- Microorganisms – bacteria, viruses, fungi, helminths
- Allergens – dust, pollen
- Organic particles – occupational exposures, pollution (e.g. diesel particulate matter)
- Toxic gases – carbon monoxide, sulphur dioxide, nitrogen dioxide
What size and type of particles can air contain?
Large particulates
• Foreign body aspiration (e.g. food, liquid, choke hazards)
Fine particulate material
• Pollution (<2.5 - 1000 μm, depending on the specific particle/source. Nanoparticles from diesel exhausts appear to be particularly damaging to the respiratory system as they are able to reach lower parts of the respiratory tree due to their small size)
• Dust (0.1-1000 μm)
• Pollen (10 - 100 μm)
Microscopic pathogens
• Fungal spores (2 - 10 μm)
• Bacteria (0.5 - 5 μm)
• Viruses (< 1 μm)
What do allergens trigger?
Allergens trigger an inappropriate and exaggerated immune system response that results in local inflammation and tissue pathology/dysfunction.
What can inhalation of particles over a long period of time cause?
Inhalation of particles over a long period can result in chronic restrictive lung disease due to the damaging effect of particle deposition within respiratory structures and the subsequent immune response triggered. Exposure to certain particles also increases the risk of lung carcinoma (cancer).
What mechanisms and features does the respiratory system have to improve immunological function?
Physical obstructions:
• Large scale = nasal hairs, nasal turbinates, branching airway structure.
• Micro scale = cilia, mucus
• 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)
What is the function of nasal hairs with the nose?
Nasal hairs within the first 1cm of the nasal passage filter out larger particles (>10μm) present in the air.
What is the purpose of nasal turbinates/ conchae
The nasal turbinates/conchae are mucous membrane-lined, ridged structures within the nasal cavity that help to warm and humidify air before it reaches the airways/lungs, as well as help to filter out particles larger than ≈ 2μm.
Where is mucas produced, what cells produce mucas and what is the purpose of it?
The upper respiratory system (airways and nasal cavity) are lined by a layer of mucus produced by submucosal glands (90%) and goblet cells (10%), which traps inhaled particles
Describe the composition of mucus?
Mucus consists of a gel with elastic and viscous properties, which consists of 97% water and 3% solids (mucin, other proteins, salts, lipids), and also contains lysozyme and various antimicrobial proteins to destroy trapped microorganisms.
How does mucas move?
The mucus gel layer lies on top of a periciliary layer (≈ 7μm deep) which provides a media of low viscosity in which cilia can beat. Maintaining sufficient periciliary layer depth is critical to effective mucociliary clearance for this reason. As the respiratory tract is lined by ciliated epithelium the coordinated beating of cilia produces a wave of movement that propels the mucus gel layer (and any trapped particles) towards the pharynx, where it is then swallowed or expelled.
When does the cilia touch the mucus layer?
The cilia only contacts the mucus gel layer during the forward stroke, as the cilia bends during the reverse stroke so that its tip passes beneath the mucus layer. Thus, the gel layer is propelled in one direction.
What are the effects of loss/impairment of mucociliary function?
On image
Describe the common pathway of neural reflexes to protect the airway from particle exposure
The basic mechanism common to each reflex involves activation of afferent sensory neurons, which 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 (e.g. the diaphragm, intercostal and abdominal muscles), the glottis (i.e. to close/open the windpipe) and airways to initiate a coordinated respiratory effort which rapidly expels air from the nasal cavity/airways/lungs.