S1: Pulmonary Defence Mechanism - What can go wrong? Flashcards
Why are the lungs a potential site of immunological vulnerability due to adaptations for gas exchange?
- Fast movement of air from atmosphere to respiratory surfaces places limits of filtering/barrier structures possible
- Efficient gas exchange requires a thin membrane innervated by blood vessels and a warm moist environment (in which microorganisms also thrive)
- The air we breathe in is not sterile/pure gas and it contains a mixture of potentially harmful organisms and particles
What are the three sizes of particles that air contains?
Large particulates
Fine particulate material
Microscopic pathogens
Give an example of large particulates
Foreign body aspiration (e.g. food, liquid, choke hazards)
Give examples of particulate material
- Pollution
- Dust
- Pollen
Give examples of microscopic pathogens
- Fungal spores
- Bacteria
- Viruses
List 4 mechanisms the respiratory system has to 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 (alveolar macrophages)
- Structural cells (epithelial cells)
- Antimicrobial proteins
- Biological symbiosis (commensals/microbiota)
What do nasal hairs and turbinates do?
They filter air and prevent particles from reaching the airways
What does the epiglottis do?
The epiglottis is the flap at the back of the tongue
It covers the airway during swallowing
What is the glottis?
Space between vocal cords
What is the role of cilia and mucus?
- Trap and remove microorganisms
- They are ever present
- Increased production of mucus when epithelium is irritated
- 90% of mucus from glands, 10% from epithelial goblet cells
- Contains antimicrobial peptides and lysozyme
Explain the factors that affect the efficiency of cilia and mucus
- Air surface liquid depth which is a layer of liquid the mucus floats on ( if too shallow the mucus sticks, if too deep the cilia can’t reach to shift the mucus )
- Cilia beat in one direction in a coordinated manner and this moves the mucus along (mucocilary escalator)
- Ciliary beat rate and direction
- Mucus volume
What is reflex mucus secretion?
- Under parasympathetic control
- Various stimuli activate sensory (afferent) neurones
- Local parasympathetic, post ganglionic neurones secrete mainly acetylcholine to induce mucus secretion
- Always involuntary
What are the three reflexes from the airway that help remove irritant or harmful particles from the airways?
Nasal Cavity: Sneeze
Larynx and Large Airways: Cough
Vocal folds: Expiration reflex
Explain the mechanism of coughing
Stimulation of mechano or chemoreceptors
Afferent impulses to cough center (medulla)
Efferent impulses via parasympathetic and motor nerves to diaphragm, intercostal muscles and lungs
Increased contraction of diaghramatic, abdominal and intercostal (ribs) muscles –> noisy expiration (cough)
Compare coughs and sneezes
Both involve:
- Deep inspiration phase ‘ahh’
- Compression phase (glottis closed)
- Expiration phase ‘choo’
- Coughs can be voluntary
- Coughs involve bronchocontriction
What is the expiration reflex?
- Immediate expiration
- Discrete stimulus: vocal cords
- No inspiration (or compression) phase
- Can be voluntary
How does branching structure of the airway help filter particles?
The airflow becomes more turbulent so more air comes in contact with the mucus and more particles are filtered out
What are alveolar macrophages (AM)?
- Large, round, mobile cells
- Crucial ‘sentry’ cells
They contribute to immunological defence and remove particles
What part of the immune system is AM cells part of?
Innate immune system
What do AM cells do?
- Recognise components of bacteria, viruses etc. without prior exposure
- Phagocytose (engulf) pathogens/particles
- Release inflammatory mediators to recruit other, specialised cell types
What do structural cells and airway/lung microbiota do?
Structural cells also help detect pathogens and alert immune system
The airway/lung microbiota also help to maintain immunological balance
SUMMARY (READ)
- Inhaled air contains harmful particles of various sizes: fine particulates (e.g. pollution), microorganisms and allergens.
- The respiratory system defensive adaptations include: physical barriers (hair, nasal turbinates), mucociliary clearance, protective reflexes (coughing, sneezing) and resident immune cells.
- Mucus (secreted by goblet cells & submucosal glands) traps inhaled particles, contains antimicrobial peptides, and is removed from the lung via coordinated cilia movement.
- Alveolar macrophages patrol the airspaces, removing particles, microorganisms and dead cells from respiratory surfaces via phagocytosis.
