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 epithelial barriersPhysical - 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 Gas exchange system 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)