3.1.6 Human defence systems

• How does the skin prevent entry of pathogens into the body?

  ● Tough / dry / dead outer layer / scabs form over cuts → acts as a barrier

  ● Antimicrobial secretions → kill pathogens

  ● Sebum / oil → repels pathogens
• How does the nose prevent entry of pathogens into the body?

  ● Hair and mucus → trap pathogens that enter
• How does the Trachea & bronchi prevent entry of pathogens into the body?

  ● Produce mucus → traps pathogens breathed in

  ● Cilia (hair-like structures) → waft mucus up to throat to be swallowed
• How does the Stomach prevent entry of pathogens into the body?

  ● Contains hydrochloric acid → kills most pathogens in food / swallowed mucus
• Describe the role of the immune system in defence against disease

  . 1. Phagocytosis - WBCs engulf and digest / destroy pathogens

  2. WBCs produce / release specific antibodies in response to antigens on surface of a pathogen

  ● Antibodies attach / bind to antigens on the pathogen (with a complementary shape)

  ● Making pathogens clump together so more can be engulfed

  3. WBCs produce / release specific antitoxins in response to toxins (poisons) released by bacteria

  ● Antitoxins neutralise / counteract toxins ● So less cell damage → don’t feel as ill
• memory cell-a type of WBC called a memory cell remains in the body after infection and produces antibodies faster & in larger quantities when it recognises the same antigen on reinfection
• why is this statement wrong?

  “WBCs eat pathogens.”

  Cells can’t ‘eat’. Instead, they engulf and destroy a pathogen
• why is this statement wrong

  "Antigens are pathogens.”

  Antigens are unique molecules on the surface of pathogens that trigger an immune response. A pathogen is a microorganism that causes disease
• why is this statement wrong?

  “WBCs release antigens.”

  Antigens are the molecules on the surface of pathogens that trigger an immune response. Antibodies are protein molecules released by white blood cells in response to a particular antigen.
• why is this statement wrong?

  “Antibodies kill antigens.”

  Antigens are not alive so cannot be killed
• why is this statement wrong?

  “Antibodies remain in the blood forever waiting to attack pathogens.”

  Antibodies break down quickly, but memory cells remain. Upon reinfection, these recognise a particular antigen and produce the correct antibodies faster and in larger quantities
• In people with cystic fibrosis mucus is thicker than the mucus produced in an unaffected person. Explain why these people have an increased risk of lung infections. (3)

  ● Pathogens breathed in stick to mucus in breathing system

  ● But cilia cannot easily move thick mucus upwards to the throat to be swallowed

  ● So pathogens pass into lungs causing infection
• Describe how injecting an antibody for [named disease] helps to treat a patient suffering with the disease. (3)

  ● Antibody binds to antigens on surface of pathogen

  ● Antibody is specific to antigen / complementary in shape

  ● White blood cells then engulf the pathogen