Pulmonary defence mechanism Flashcards
The movement of large volumes of air from atmosphere to respiratory surfaces via the airway requires
Fast movement of air in and out of the lungs (few barriers/filters)
EFficient gas exchange (large SA< thin membrane, innervation by blood vessels, warm, moist environment)
What harmful organisms and particles exist in air
Microorganisms - Bacteria, viruses, fungi, helminths
Allergens - dust, pollen
Organic particles - Occupational exposures, pollution
Toxic gases - CO, sulfur dioxide, nitrogen dioxide
Large particulates - Foreign body aspiration (food, liquid)
Fine particulate material - Pollution (nanoparticles of diesel exhaust), dust, pollen
How may inhaled particles damage the respiratory system
Allergens trigger an exaggerated immune system response, local inflammation and dysfunction/pathology
Some organic particles result in chronic restrictive lung diseases such as fibrosis, due to particle deposition in respiratory structures.
What adaptations limit infection
Nasal hairs, nasal turbinates, branching airway structure
Cilia, mucus
Coughing, sneezing, expiratory reflex
Lung resident immune cells, structural cells, antimicrobial proteins
Biological symbiosis
Describe the function of nasal hair and turbinates
Nasal hairs filter out larger particles in the air. The turbinates are mucous membrane-lined and ridged, which warm and humidify air as well as filter out large particles.
Decreased nasal hair density linked to increased asthma risk
Describe function of cilia and mucus
Traps inhaled particles, and destroys trapped microorganisms. The beating of cilia produces movement that propels the mucus gel layer towards the pharynx, where particles are swallowed or expelled.
What happens if mucociliary clearance is impaired
In cystic fibrosis/chronic bronchitis, mucus clearance impaired, leading to recurrent respiratory infections as well as inflammation/tissue damage
Describe the function of protective reflexes
Trigger rapid expulsion of air and therefore particles, activated by nociceptors within upper resp tract
Describe the basic mechanism common to each reflex
ACtivation of afferent sensory neurons, impulse to breathing centres. EFferent signals to specific respiratory muscles, the glottis and airways to expel air
Describe sneezing
Stimulation of sensory receptors within nasal cavity, deep inspiration, compression (buildup of pressure) and final expiration phase
Describe coughing
STimulation of larynx receptors and large airways. Involves bronchoconstriction to increase expulsion pressure
Describe the laryngeal reflex
Short forcible expiratory effort, without inspiration, triggered by sensory receptors within vocal folds.
Prevents foreign bodies entering airways, expels phlegm.
Describe how the branching structure of airways is useful
Increases filtering of air, prevents particles reaching lower respiratory structures.
Describe resident immune cell defence for respiratory system
Immune cells provide defence and coordinate immune responses, remove deposited particles
Why are alveolar macrophages important
AM phagocytose pathogens, foreign materials and cell debris, residual material removed by lymphatic system.
Macrophages help trigger further inflammation if they cannot clear some particles, and secrete cytokines and other inflammatory mediators.
Some macrophages act as antigen presenting cells.
