Respiratory defence mechanisms

airway defence mechanisms

concerned primary with defending against inhaled particles

• filters particles from inhaled air

• prevents particles containing and damaging epithelial surfaces

• removal of particles

airborne particles

inert matter

water droplets

infectious agents

allergens

airway defence mechanisms

1. aerodynamic filtration

2. mucociliary esculator

3. antibacterial agents

4. IgA

5. protective reflexes

6. leucocytes

aerodynamic filtration

coiled turbinates leads to airflow turbelence causing particles >10um to impact onto airway mucosa

bronchi filter out most particles > 3um

particles ~ 1-5um are deposited in bronchioles and alveoli

mucociliary esculator

most upper airways lined by mucus carpet and swept by cilia

mucus

• traps and transports particles from lower airways to pharynx

• physical barrier

• prevents dehydration

• dilutes soluble gases

• contains antibacterials

= lysozyme - bacteriolytic protein that hydrolyses peptidoglycan wall

= Fe-binding protein synthesised by neutrophils and ep cells, retarding bacterial and fungal growth

factors affecting mucociliary carpet

change in viscosity of mucus

• temp, dehydration

• inflammation

injury to epithelium

• trauma, infection

• chronic irritation may = cell type change

protective reflexes

cough/sneeze

alveolar defences

macrophages

• alveolar

• interstitial

• intravascular

role

• phagocytose particles and agents

• recruit neutrophils

• coordinate inflammation

• ascend mucociliary escalator

diseases of upper airways

developmental abnormalities

circulatory disturbances

inflammatory conditions

neoplasia

development abnormalities

cleft palate

• failed closure of palatine shelves = aspiration of food

brachycephalic airway syndrome

• combination of anatomical problems =

• stenotic nares

• everted laryngeal saccules

• elongated soft pallate = airway obstruction, cyanosis and syncope

circulatory disturbances

epistaxis - bleeding from nose

sources

• upper airways

• lower respiratory tract

causes of haemorrhage in upper airways

inflammation

infection

trauma

neoplasia

clotting defects

• VWD or thrombocytopenia

5 typical sings of inflammation

redness - due to blood vessel dilation and congestion/ hyperaemia/ haemorrhage

swelling - due to infiltration by cells and fluid leakage

heat - due to increased blood supply

pain - due to compression of tissue pressure sensors

loss of function - variable depending on site

acute inflammation - general principles

similar response throughout airways

vasodynamic changes - redness, swelling, exudate

increased secretions - serous, mucus

inflammation classified by type of exudate

serous

clear watery discharge

easily missed

mild - increased production from mucoserous glands

mucosal hyperaemia and oedema

catarrhal

viscous, mucoid

increased mucoserous secretions

minor numbers of inflammed cells

fibrinous

thick, fibrinous and haemorrhagic discharge

increased vascular permeability ± necrosis

purulent

thick, white, green, brown

many inflammatory cells esp neutrophils and cell debris

chronic inflammation = pathological changes

mucosal hyperplasia

• goblet cell hyperplasia

• seromucous gland hyperplasia

chronic inflammatory cells

• macrophages, lymphocytes, plasma cells

fibroplasia

epithelial metaplasia

2o to chronic irritation eg bronchitis, get respiratory epithelial metaplasia ie. ciliated columnar → stratified squamous ep

polyps secondary to chronic inflammation

nasal/ nasopharyngeal polyps

• horses and cats

• cat - arise in auditory tube or tympanic bulla

• may extend into pharynx or along external ear canal

• resp noise/ dysphoea

nasopharyngeal polyp - cat

causes of upper airway inflammation

irritants/ allergens

• pollen

• dust

• fomites

foreign bodies

parasites

infectious agents - viral, bacterial, fungal

some viral agents assoc with inflammation of URT

Feline herpesvirus 1 Flu →

Feline calicivirus Flu

Equine herpesvirus 1 + 4

Equine influenza virus

Canine distemper virus

Canine adenovirus 2 KC with BB

Canine parainfluenza virus KC with BB

Bovine herpesvirus 1 (Infectious Bovine Rhinotracheitis)

infectious bovine rhinotracheitis

due to bovine herpesvirus 1

aerosol infection

mixed, stressed and overcrowded

in severe cases = necrosis and fibrinous inflammation of mucosa

IBR - spread of virus throughout upper respiratory tract

neutralising antibodies and cell-mediated immunity responses - over 1-2 weeks

resolution of viral infection and elimination of bacteria

healing

strangles

Streptococcus equi

Colonises nasopharyngeal mucosa

initial serous nasal discharge becomes purulent typical of S. equi infection

lympahatic spread to lymphnodes

absesses within (parotid) LNs can rupture and drain to surface

guttural pouch empyema

sequel to strangles

• abscessated retropharyngeal LNs ruptures into guttural pouch creating a pus filled cavity

can be caused by other bacteria

• e.g rhodococcus equi

fungal infections - aspergillus fumigatis

dogs, horses, birds

often predisposing immunosuppression

fibrinonecrtotic/ granulomatous inflammation and bone lysis due to cytolytic enzymes from fungus

guttural pouch mycosis

Aspergillus fumigatis

Infection causes severe infm + necrosis

Often unilateral

complications =

• damage to cranial nerves = paralysis of facial muscles, tongue, pharynx, larynx

• erosion of blood vessels - haemorrhage may be fatal

nasal carcinoma

Ph: Epithelial cells, mostly glands, of the nasal mucosa

Pr: Long-skulled dolichocephalic dog breeds

Sp: Dog, >80% malignant tumours.

Dist: Nasal cavity > sinuses

Gr: Proliferative, destructive masses, white + friable