1.1 defensive barriers
epithelial surfaces
- Respiratory tract
- Skin
- Alimentary tract
- Urogenital tracts
why epithelial surfaces are susceptible to environmental factors that can cause disease
- Epithelial tissue at external surfaces susceptible to environmental insults trauma & infection
- Mucous membranes particularly susceptible due to thin walls (required for physiological function)
Mucous
- Water & electrolytes
- Glycoproteins & lipids
- Antimicrobial compounds
- Transferrin
- Lactoferrin
- Lysozyme
- Antibodies (IgA)
- Antioxidants
- Superoxide dismutase
- Catalase
- Glutathione peroxidase
Routes of infection
- Horizontal transmission
- Direct contact
- Aerosol (e.g. kennel cough)
- Oro-faecal (e.g. handling faeces & infecting feed)
- Vector-bourne (pathogen uses arthropod host to spread from animal to animal, e.g. ticks & lyme disease)
- Vertical transmission
- Direct contact (pathogen crosses placental barrier to infect foetus, e.g. bovine virus diarrhoea - BVD)
adaptations of skin, respiratory tract & alimentary tract
Defensive barriers
Physical barriers - skin
- epithelial barriers
- Physical - skin
- Physiological - mucous membranes
- Biochemical - gastric acid
- Immunological - macrophages
- Keratinocytes replicate to generate stratified squamous keratinised epithelium, has receptors binding to microbes, causing signalling cascade, leading to production of various soluble factors (w/ antimicrobial properties)
- TRIGGERING INFLAMMATION - produce cytokines (immunological hormones) & chemokines (cell migration factors)
- Melanocytes protect from UV damage
- Langerhans cells - tissue-resident macrophages present in all layers of epidermis
- Sebaceous glands & sebum - water repellent, contains fatty acids & has anti-microbial components
Respiratory tract
- Mucociliary escalator
- Continual movement of cilia stops microbes from forming colonies by moving them continually
- Host become immunocompromised without this - can be caused by toxic compounds, potentially causing pneumonia
- Viral infection, trauma (from dust) and toxins (ammonia) can occur if mucociliary escalator is compromised
- Alveolar macrophages
- Main line of defence against inhaled microbial pathogens & inanimate particles
- Derived from blood monocytes & interstitial macrophages
- Short lifespan in alveoli
The respiratory system as a defensive barrier
- Conductive system:
- Nasal cavity
- Pharnyx
- Larynx
- Trachea
- Bronchi
- Transitional system
- Bronchioles
- Gas exchange system
- Alveoli
Alimentary tract
- Oral cavity & oesophagus
- Function - prehension, mastication & digestion (salivary enzymes)
- Protection needed against trauma & infectious agents
- Physical barrier - stratified squamous epithelium
- Biochemical barrier - lysozyme in saliva
- Stomach
- Sterilisation & digestion of food
- HCl acid (pH 2)
- Pepsin (protease)
- Mucous (protect epithelium)
- Regulatory peptides
- Small intestine
- Cryptidins (similar to denfensins)
- Toxic to bacteria
- Synthesised by Paneth cells present in intestinal crypts
- Immune defence of GIT
- Gut-associated lymphoid tissue - produces immune responses
- Specific mucosal protective antibody (IgA)