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