Defense against diseases - Immune System

• Pathogens as the Cause of Infectious Diseases


  • Pathogens are disease-causing organisms that can infect humans, including viruses, bacteria, fungi, and protists.
  • Archaea, a type of single-celled microorganism, are not known to cause any diseases in humans.
  • Careful observation during 19th-century epidemics, such as childbed fever and cholera, led to important breakthroughs in the control of infectious diseases.
• Hemostatic system process involves the following steps

  1. Vasoconstriction: Blood vessels constrict to reduce blood flow.
  2. Platelet activation: Platelets adhere to the damaged tissue and release clotting factors.
  3. Coagulation cascade: A series of enzymatic reactions leads to the formation of a fibrin clot, which seals the wound.
  4. Fibrinolysis: The clot is eventually broken down and the wound heals.

  
• What are pathogens?


  Microorganisms that cause infectious diseases
• What are the main types of pathogens?


  • Viruses
  • Bacteria
  • Fungi
  • Protists
• Why are Archaea not considered pathogens in humans?


  They are microorganisms but do not cause diseases in humans
• What is the germ theory of disease?


  The concept that microorganisms cause diseases
• What are the primary defenses against pathogens?


  • Skin
  • Mucous membranes
• How does the skin act as a barrier against pathogens?


  • Physical Barrier: Tough, keratinized outer layer
  • Chemical Barrier: Produces substances that deter pathogens
• What is the function of mucous membranes?


  • Line body cavities exposed to the external environment
  • Produce mucus to trap pathogens and contain enzymes that destroy them
• How did careful observation contribute to the understanding of infectious diseases?


  • Discoveries during the childbed fever epidemic in Vienna
  • Insights from the cholera outbreak in London
• What is the purpose of blood clotting?


  To seal cuts in the skin and prevent blood loss
• What are the steps involved in the blood clotting process?


  1. Release of clotting factors from platelets
  2. Cascade pathway activation
  3. Conversion of fibrinogen to fibrin
  4. Trapping of erythrocytes to form a clot
• What do platelets release when they encounter damaged blood vessels?


  Clotting factors
• What is the cascade pathway in blood clotting?


  A series of chemical reactions triggering each other
• What is the role of thrombin in blood clotting?


  It converts fibrinogen into fibrin
• How does fibrin contribute to clot formation?


  It forms a mesh-like structure trapping red blood cells
• What are the two tiers of the immune system?

  • Innate immune system (general infantry)
  • Adaptive immune system (specialized forces)
• What are the characteristics of the innate immune system?


  • Responds to broad categories of pathogens
  • Does not change during an organism's lifetime
  • Fast-acting but less specific
• What is an example of the innate immune system?


  Phagocytes that engulf and destroy pathogens
• What are the characteristics of the adaptive immune system?


  • Responds specifically to particular pathogens
  • Builds memory of encountered pathogens
  • Becomes more effective over time
  • Slower initial response but highly specific
• How does the adaptive immune system provide long-lasting immunity?


  By remembering previous encounters with pathogens
• What is the specificity of the innate immune system compared to the adaptive immune system?


  Innate is broad, while adaptive is specific
• What are the key differences between the innate and adaptive immune systems?

  • Specificity: Innate (broad) vs. Adaptive (specific)
  • Memory: Innate (no memory) vs. Adaptive (builds memory)
  • Response Time: Innate (fast) vs. Adaptive (slower initially, faster later)
  • Effectiveness Over Time: Innate (constant) vs. Adaptive (improves)
• How do phagocytes contribute to infection control?


  They actively seek out and devour pathogens
• What type of movement do phagocytes use to reach infection sites?


  Amoeboid movement
• How do phagocytes recognize pathogens?


  They identify various pathogens as foreign invaders
• What is phagocytosis?


  The process by which a phagocyte engulfs a pathogen
• What happens after a phagocyte engulfs a pathogen?


  Lysosomes fuse with the vesicle to break down the pathogen
• What are the two main types of lymphocytes in the adaptive immune system?

  • B-lymphocytes (B-cells)
  • T-lymphocytes (T-cells)
• What are key points about B-lymphocytes?


  • Circulate in the blood and are contained in lymph nodes
  • Each produces a specific type of antibody
  • A vast number of different B-lymphocytes allows for a wide range of antibodies
• What is the antibody production process in B-lymphocytes?


  1. Encounter a specific antigen
  2. Activation if the antigen matches the B-cell's antibody
  3. Multiplication and differentiation into plasma cells
  4. Plasma cells produce large quantities of the specific antibody
• Why is the diversity of B-lymphocytes important for the immune system?


  It allows for a wide range of antibodies to be produced
• What are antigens?


  Molecular "name tags" that trigger the immune response
• What is the nature of antigens?


  • Most are glycoproteins or proteins
  • Usually located on the outer surfaces of pathogens
• What is the function of antigens on pathogen surfaces?


  • Helps the immune system identify invaders
  • Important for blood typing on erythrocytes
• How do B-lymphocytes get activated by Helper T-lymphocytes?


  • Antigen-specific recognition
  • Direct interaction with the specific antigen
  • Contact with an activated helper T-cell
• What are the results of B-cell activation?


  • Production of antibodies
  • Formation of memory cells
• What is the activation process of B-lymphocytes?


  1. Antigen enters the body
  2. B-cell recognizes and binds to the antigen
  3. Helper T-cell recognizes the same antigen
  4. Activated helper T-cell interacts with the B-cell
  5. B-cell multiplies and differentiates into plasma cells and memory B-cells
• Why is the two-step activation process important for the immune response?


  It ensures specificity and regulation, preventing unnecessary reactions
• What happens during the multiplication of activated B-lymphocytes?


  They undergo rapid multiplication to form clones