Immunity

• Non-Specific


  External Defence
• First Line of Defence

  Non-specific defence may be physical (also known as mechanical) barrier or a chemical substance
• Non-specific external defences


  • stomach acid
  • good gut bacteria
  • skin
  • tears
  • antibacterial enzymes in saliva
  • mucus
  • Cilia – hair like projections
• Stomach acid


  • Low pH kills harmful microbes
• Skin


  • Prevents entry
  • Continuously shed (totally replaced approx. every 4 weeks)
  • Contains sebaceous glands which produce an oily sebum (fatty acids resistant to bacteria)
  • Sweat contains the powerful anti-microbial enzyme lysozyme
• Resident flora & fauna

  • Discourages foreign microorganisms from establishing themselves
  • Makes the skin slightly acidic (pH 3 – 5) which is unsuitable for many foreign organisms
• Ear


  • Modified glands at the entrance to the auditory canal secrete cerumen (ear wax) which is thought to repel insects and inhibit bacterial growth
• Eyes


  • Protected by the brows, lashes and lids
  • Blinking prevents some harmful substances entering the eye
  • Tears have a flushing action, washing out the eye
  • Tears contain lysozyme, powerful antimicrobial
  • Salts inhibit pathogens
• Respiratory Tract


  • Coarse hairs line the nostrils to slow the air and trap the largest particles of dust & small insects
  • Nasal fluids contain lysozyme which is a powerful antimicrobial
  • Sticky mucus secreted by goblet cells coats the mucous membrane of the nasal cavity & airways
  • Microscopic cilia line the upper respiratory tract and sweep the mucus layer up the trachea and into the throat
  • Macrophages in the lung tissue destroy pathogens which escape the mucus trap and enter the alveoli
• Gastrointestinal Tract


  • Saliva contains lysozyme (antimicrobial)
  • Gastric Juices: hydrochloric acid in our stomachs (avg. pH 2) kills most as well as protein digesting enzymes (proteolytic enzymes)
  • Sticky mucus lining and the scouring action of the stomach moving material around in the stomach make it very difficult for microbes to becomes established
  • Anus – mucus traps pathogens
• Urinogenital Tract


  • Flushing action of urine which tends to be slightly acidic at pH 6
  • Vagina has resident bacteria and fungi which secrete lactic acid as a by product making the vagina fluid acidic (pH 4) which discourages most microbes
  • Cervix is blocked by a mucus plug most of the monthly cycle
• Protective Reflexes


  1. Sneezing

  2. Coughing

  3. Vomiting

  4. Diarrhoea
• Reflex


  An automatic, involuntary response to a stimulus
• Reflexes help protect the body from injury and infection