human defence systems

• The SKIN


  • Provides a protective BARRIER against pathogens.
  • Produces ANTIMICROBIAL SUBSTANCES (sebum) to actively kill potential threats.
• The NOSE


  • HAIRS and MUCUS in the nose serve as physical traps for dust, microbes, and other particles.
  • Helps prevent the entry of pathogens into the respiratory system.
• The TRACHEA and BRONCHI


  • Secrete MUCUS to capture and trap pathogens.
  • Lined with CILIA, tiny hair-like structures that move mucus loaded with trapped pathogens OUT OF the respiratory system to the back of the throat. From there it is swallowed and goes into the STOMACH.
• The STOMACH:


  • Produces HYDROCHLORIC ACID, a strong acid that destroys pathogens ingested through food or drink.
• If these defences fail and the pathogens enters the blood stream of a person, they are said to be INFECTED. From this stage the IMMUNE SYSTEM kicks in to try and kill the pathogens.
• PHAGOCYTOSIS:

  • A process where WHITE BLOOD CELLS (phagocytes) ENGULF and DIGEST invading pathogens.
  • The phagocytes goes up to a pathogen and changes its shape to SURROUND the pathogen. It then releases ENZYMES to digest it.
• Antigens


  Unique markers on the surface of pathogens
• Lymphocytes


  White blood cells that can identify antigens
• Antibody production


  1. Lymphocytes produce antibodies

  2. Antibodies bind to antigens and mark them for destruction

  3. Phagocytes find and engulf marked pathogens
• After pathogens are killed, most lymphocytes that produced the antibodies die off
• Memory cells


  Lymphocytes that remain in the body and rapidly produce more antibodies if the pathogen reappears
• Memory cells remain in the body


  Person is immune to the disease and pathogen
• ANTITOXIN PRODUCTION:

  • These help with BACTERIAL infections
  • Bacteria produce poisons known as TOXINS which cause harm to body cells
  • ANTITOXINS are substances that neutralise the toxins released by invading bacteria.