Human defence systems

• Non Specific defence systems of the human body

  • Skin
  • Nose
  • trachea and bronchi
  • stomach
• Role of the immune system in the defence against diseases

  If a pathogen enters inside the body, the immune system tries to destroy that pathogen
• White blood cells are the most important part of your immune system
• the white blood cells help to defend against pathogens

  • Phagocytosis: white blood cells can engulf foreign cells and digest them
  • antibody production
  • antitoxin production: these counteract toxins produced by invading bacteria
• Antigen

  Unique molecules on the surface of invading pathogens
• Antibody production


  1. White blood cells come across a foreign antigen

  2. White blood cells start to produce proteins called antibodies

  3. Antibodies lock on to invading cells

  4. Other white blood cells find and destroy the cells with antibodies attached

  5. Antibodies produced are specific to that type of antigen
• Antibodies are then produced rapidly and carried around the body to find all similar bacteria or viruses
• If the person is infected by the same pathogen again

  The white blood cells will rapidly produce the antibodies to kill it. The person is naturally immune to that pathogen and won’t get ill
• Non specific defence system: skin

  • Acts as a barrier to pathogens
  • secretes anti microbial substances which kill pathogens
• Non specific defence system: nose

  Contains hair and mucus that trap particles that could contain pathogens
• Non specific defence system: trachea and bronchi

  • secrete mucus to trap pathogens
  • lined with cilia - hair like structures which waft the mucus up to the back of the throat where it can be swallowed
• Non specific defence system: stomach

  Produces hydrochloric acid - kills pathogens that make it far from the mouth