1.19.3.10 - Respiratory Tract Defence Mechanisms
structures of the respiratory tract
nares and nasal cavity
paranasal sinuses
pharynx
larynx
trachea
bronchi
bronchioles
alveoli
Functional characteristics of the respiratory tract
olfactiopn nd taste
vocalisation
walm, filter and humidifiy air
conduct o2 and co2
Defence of the lungs: to exclude or remove foreign agents
prevent entry
swallow
trapping
sneeze/cough out
antimicrobial compounds
eliminate via immune response
defence of the lungs - prevent entry
non-spedicif vs specific degence
non specififc
specific
recongition of particles by imune system
lymph nodes/tissues
mucosal immunity
removal of particles
physical and anatomical
lubricants
refelces
antimicrobial compounds
head position allows drainage e.g. grazing
nares
size
distriburion of hairs within
position
nasal cavity
narrow passages
particle deposition
turbulence
swallow
close proximity of air and ood passages in the head
swallowing of foreing particles easily
destroyed by stomach acid
nasal cavity
larynx/pharynx/epiglottis
trapping
cilia
mucous
Movement towards pharynx.
Symmetric & coordinated movement results in waves of motion.
Nasal passages to bronchioles, (excluding pharynx as squamous epithelium).
Aqueous sol layer which covers the cilia.
Anti-bacterial lysozyme.
Mucoid gel layer which the tips of the cilia touch.
produced by goblet cells
goblet cells
present in nasal, tracheal, bronchial epithelium, not terminal bronchioles
produce a viscous secretion which forms a gel layer over the sol
submucosal glands
neck of gland opens at epithelial surface
present in bronchi, not bronchioles
contain serous secretions
clara cells
in alveoli (lower resp tract) serous mucin
sneezing/coughing
cough reflec
sneeze reflex
to remove foreign objects or irritants
Clears trachea & bronchi.
Clears nasal passages.
Lower rep tract.
Upper resp tract.
antimicrobial compunds
lysozymes
defensins
Produced by macrophages, neutrophils & epithelium.
Electrically attracted to the microbe, embed into the membrane & form a pore.
Short chains of amino acids.
Anti-bacterial enzymes.
Break down of bacterial cell walls.
In mucous.
Kill bacteria, fungi & enveloped viruses.
Draining lymph nodes of the head and respiratory tract
thorax
head
deep in chest
can be viewed radographically
tracheobronchial
mandibular
retropharyngeal
parotid
meat hygiene inspection
Lymphoid tissues in respiratory tact
MALT
BALT
Aggregation of lymphocytes under ciliated epithelium
Strategically located at bifurcations of bronchi (turbulence & deposition of particles) to sample deposits
Aggregations of lymphocytes beneath non-ciliated epithelium
Alveola leucocytes
healthy lungs
diseased lungs
macrophages
lymphocytes
occasional neutrophils
low levels of mucous
lymphocytes
neutrophilia
macrophages
excess mucous secretions
Hemosiderophages
alveolar macrophages that have ingested and digested red blood cells
Diagnostic tools: Bronchoalveolar or Tracheal wash
commonly used to assess the respoiteraoty health of race horses
broncioalveolar wash (endoscope)
tracheal wash
natural u bend
in equine tracea
transparency
colour number (wbc/rbc)
viscosity
wbc
frothy surfactant
Innate immune responses in respiratory tract
molecules
Leucocytes
surfactants
cytokines
defensins
complement
lysozymes
inflammotry mediatiors
originate from blood & interstitium
carried from lung to trachea
neutrophils (phagocytosis)
basophils (degradation)
eosionphils (degranulation)
macrophages (phagocytosis)
mast cells (degranulation)
Adaptive immune responses in respiratory tract
mucosa
lymphocytes
antibodies
Mucosal synthesis of IgA
diffusion of IgG from serum
all classes except IgM
Circulating in blood & interstitium,
Intraepithelial lymphocytes are associated with mucosal membrane
adjacent to site of particle deposition
rapid response
can be recruited to the RT epithelium & lumen
Fate of inhaled particles in the respiratory tract
Stimulation of receptors / reflexes: sneeze or cough / glottis closure
Stimulation of immune responses / antimicrobial agents in mucus / secretions
Trapped in mucus and transported via mucociliary escalator
swallow
swallow
killed
bronchiolar spasm
examples of allergic inflammation in RT
casues
Feline asthma
Equine asthma (recurrent airway obstruction, heaves, chronic obstructive pulmonary disease)
Recent or current infection (bacterial, viral, parasitic)
allergy
Irritation (particles, fumes)
Both are inflammatory diseases
Both lead to bronchoconstriction /bronchospasm
Allergic reaction -> Bronchospasm
IgE bind to mast cells/ basophils in mucous membranes
If allergen encountered again, mast cells/ basophils degranulate and release a large amount of histamine & other inflammatory mediators
IgE antibodies have been formed since B-cell first came in contact with antigen
Inflammatory mediators lead to smooth muscle contraction around bronchioles, directly and via CNS
Activation of B-cells by allergen leads to a Type I hypersensitivity reaction:
Bronchoconstriction
Allergens themselves are harmless but activate T- and B- cells
summary
Major draining LNs include the parotid, mandibular, retropharyngeal and tracheobronchial LNs.
Leukocytes are generally either located in MALT/GALT or in alveola spaces.
Defences of the RT include prevention of entry (head position, nares, nasal cavity), swallowing (nasal cavity, larynx/pharynx/glottis), trapping (cilia, mucus), sneezing/coughing, antimicrobial compounds (defensins, lysozyme) & immune responses.
Inflammatory mediators and the CNS contribute to bronchiolar spasms/bronchoconstriction. Treatment strategies include agonists/antagonist, corticosteroids, mucokinetics, hyposensitisation & vaccination
treatment strategies
reduce inflammation
stimulate mucociliary action
prevent pronchoconstrictione
reduce allergic reaction
promote bronchodilation
prevent infection
agonist drugs
antagonist drugs
corticosteroids
mucokinetics
hyposensitisation
vaccination
stimulate specific receptors
inhibit specific receptors
anti-imflammatoy
timulate mucus and indirectly, ciliary motility
modulate immune response
memory cells in adaptive immune response
to encourage drainage of respiraoty tract
antibodies and lymphocytes
passive immunity & vaccination
innate immune system
mucus
lysosyme
head position/cilia
coughing/sneezing
role of the CNS
srill under investigation
smooth mucle contraction and bronchoconstriction
afferent vs efferent
allergy = degranulation
parasympthetic nervous sytem ( vagus nerve X)
neutrotransmitters ++ (chemical messengers)
imflammatory mediators ++
stimulation of neurons