Primary defence, C3.2.1, C3.2.2, C3.2.3

• What is a disease?

  Diseases are illnesses that have characteristic symptoms
• What are the three causes of disease?

  Genetic (one's alleles)

  Environmental (chemicals, radiation)

  Pathogen infection
• What are pathogens?


  Pathogens are microorganisms that cause disease. They may be bacteria, fungi, Protista or viruses, and are passed from one infected organism to another, directly or indirectly.

  Pathogens must be able to multiply within the body. Viruses, despite not being able to reproduce themselves, are still replicated by host cells and cause diseases, so are classified as pathogens.
• What are some examples of pathogens and their diseases?

  Bacteria- tuberculosis, leprosy

  Fungi- athletes foot, thrush

  Protista- malaria, sleeping sickness

  Viruses- influenza, measles

  Prion- Spongiform encephalopathies
• What is the primary defence?

  A primary defence is the body's first line of defence against pathogens - it prevents pathogens from entering the body in the first place.

  The primary defence of the body against entry of pathogens is the skin.
• What is the role of keratin in skin?

  The skin's outermost layer, covered in a tough later of dead cells with keratin, provides a physical barrier that makes the entry of pathogens very difficult.
• What is the role of sebaceous glands in skin?

  Sebaceous glands are associated with hair follicles on the skin, and secrete sebum, which both maintains skin moisture and lowers skin ph. Low pH inhibits the growth of bacteria and fungi.
• What is the mucous membrane?

  Some areas of the body (vagina, lung airways) are covered with a mucous membrane. This type of skin is softer and thinner, and secretes mucus, which is a sticky solution of glycoproteins. This mucus acts as a physical barrier for pathogens, as they become trapped in it and are either engulfed or expelled. The mucus also has antiseptic properties, as it contains the anti-bacterial enzyme lysozyme that breaks don bacterial cell walls. .
• What is blood clotting?

  Clotting seals a wound, preventing a further loss of blood and decrease in blood pressure.

  It also prevents entry of pathogens to the body until new tissue has grown to heal the abrasion.

  Blood clotting involves a cascade of reactions, each one producing a catalyst for the next reaction. This allows blood to clot very quickly.
• What is the role of platelets in blood clotting?

  Platelets have two roles:

  Form a temporary plug: Platelets stick to the damaged area and to each other, forming a platelet plug.

  Release clotting factors: Platelets release chemicals that activate other clotting factors in the plasma to start the clotting cascade.
• What is the blood clotting cascade?

  Platelets release chemicals that activate other clotting factors in the plasma to start the clotting cascade.

  Then, these factors cause the plasma protein prothrombin to be converted into the active enzyme thrombin.

  Thrombin converts the soluble plasma protein fibrinogen into insoluble fibrin.

  Fibrin strands form a mesh that traps more platelets and RBCs, creating a stable blood clot that seals a wound.