11.1 Defence Against Infectious Disease Flashcards

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1
Q

Describe the process of blood clotting

A
  • Clotting (haemostasis) is a mechanism that prevents the loss of blood from broken vessels
    • Damaged cells and platelets release chemical signals called clotting factors which trigger a coagulation cascade
    • Clotting factors convert the inactive zymogen prothrombin into the activated enzyme thrombin
    • Thrombin catalyses the conversion of the soluble plasma protein fibrinogen into an insoluble form (fibrin)
    • Fibrin forms an insoluble mesh of fibres that trap blood cells at the site of damage
    • Clotting factors also cause platelets to become sticky, which then adhere to the damaged region to form a solid plug called a clot
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2
Q

State the functions of blood clotting

A

To prevent further loss of blood from broken vessels and to block entry to foreign pathogens

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3
Q

Outline the principle of challenge and response

A

Immunity to a specific pathogen is only developed once the body is challenged by that pathogen
• When challenged, the body responds with both a specific and non-specific immune reaction
• Non-specific immune cells (macrophages) engulf the pathogen, incorporate its antigens into its membrane, and present the antigens to lymphocytes (non-specific response)
• These lymphocytes can then produce antibodies to specifically target the pathogen (specific response)

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4
Q

Outline the principle of clonal selection

A

Macrophages must present antigens to the appropriate, specific B cell (lymphocyte) so that it can begin to clone itself into plasma and memory cells, and produce the needed antibodies
• Each B cells has a specific antigen receptor on its surface which is capable of recognising a specific antigen
• When macrophages present antigens to lymphocytes, only the specific B cell will activate and clone, meaning only the needed antibodies are produced
• The majority of B cell clones will differentiate into antibody-producing plasma cells, while the minority will become memory cells
• Because pathogens may contain several antigenic determinants, several B cells may become activated by a single pathogen (polyclonal activation)

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5
Q

Outline the principle of memory cells

A

Allow the body to have long term specific immunity against the pathogen, even after B-cells and antibodies are gone
• Memory cells remain in the body for years (or even a lifetime)
• If a second infection of the same antigen occurs, the memory cells react faster and more vigorously than the initial response, such that the symptoms of the infection do not normally appear
• Because the individual does not present symptoms of infection upon exposure, they are thus said to be immune

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6
Q

Define active immunity

A

Immunity due to the production of antibodies by the organism itself after the body’s defence mechanisms are stimulated by antigens

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7
Q

Define passive immunity

A

Immunity due to the acquisition of antibodies from another organism in which active immunity has been stimulated
• Can be achieved via placenta, colostrum (early breast milk), or vaccination

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8
Q

Define innate immunity

A

Immunity from birth due to genetic factors

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9
Q

Explain antibody production (HL)

A
  • Pathogen enters body
    • Pathogen engulfed by macrophage, which presents pathogen’s antigens on its surface
    • Macrophage binds to and activates helper T cell
    • Helper T cell activates B cells
    • B cell clones, differentiating into plasma cells and memory cells
    • Plasma cells secrete large amounts of antibodies
    • Memory cells remain in body and provide long term specific immunity
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10
Q

Describe production of monoclonal antibodies

A
  • Monoclonal antibodies are antibodies derived from a single B cell clone
    • An animal (typically a mouse) is injected with an antigen and produces specific plasma cells
    • The plasma cells are removed and fused (hybridised) with tumour cells capable of endless divisions (immortal cell line)
    • The resulting hybridoma is capable of synthesising large quantities of specific antigen as it continues to divide and grow
    • Antibodies can then be extracted and purified for use in diagnosis and treatment
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11
Q

Describe a diagnostic use for monoclonal antibodies

A

Can be used to test for malaria
• The monoclonal antibodies can bind to the malaria antigens
• A blood sample is taken and placed on a test plate covered in antibodies
• An enzyme is added which causes the plate to change colour in the presence of antibodies bound to antigens

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12
Q

Describe how monoclonal antibodies can be used for treatment

A

Can treat anthrax
• Anthrax bacteria secrete poisons, and monoclonal antibodies can be injected to neutralise the toxins until the body has time to respond and produce its own antibodies

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13
Q

Explain the principle of vaccination

A

Vaccinations induce artificial specific immunity by triggering the production of memory cells
• A vaccine contains a dead or weakened form of the pathogen and is (usually) injected
• The modified version of the pathogen does not cause the individual to develop disease symptoms
• The body responds to the vaccine, initiating a primary immune response, resulting in the production of memory cells
• When exposed to the actual pathogen, the memory cells trigger a secondary immune response that is much faster and stronger
• Vaccines confer long-term immunity, however because memory cells may not survive a life time, booster shots may be required

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14
Q

Discuss the benefits of vacination

A
  • Protection for the individual from an infection and its harmful effects
    • Protection for a community through herd immunity
    • Diseases can be eradicated entirely (smallpox)
    • Can limit the spread of infectious diseases, preventing epidemics
    • Reduced economic burden of healthcare for the sick
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15
Q

Discuss the dangers of vaccination

A
  • Vaccinated individuals may show mild symptoms of the disease
    * Individuals may present allergic/hypersensitive reactions
    • Possible toxic side-effects of mercury-based preservatives used in vaccines
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16
Q

Outline the principle of immunity

A
  • Immunity s the ability of an organism to resist infection due to the presence of specific antibodies
  • Immunity can be active or passive
  • Passive immunity is due to receiving antibodies from an external source
  • Active immunity results from facing an infection directly
  • Pathogen invades body
  • Leads to clonal selection and the formation of B memory cells
  • B-cells produce specific antibodies
  • If the same pathogen enters the body again, memory cells will activate and produce antibodies faster and in greater amounts than the first time