The Immune System

Biology

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  • Created by: alex
  • Created on: 25-05-11 11:35

The Immune System

PRIMARY DEFENCES
Skin

  • Acts as a physical barrier blocking pathogens from entering the body
  • Acts as a chemical barrier by protecting chemicals that are antimicrobial

Mucus Membranes

  •  Pretect body openings that are exposed to the environment
  • Membranes secrete mucus to trap pathogens and contain antimicrobial enzymes.

THE IMMUNE SYSTEM

An immune response is the body’s reaction to a foreign antigen.

Antigens – molecules found on the surface of cells

When a pathogen enters a body, the antigens on its surface are identified as unknown.

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The Immune Response - 1

Phagocyte (e.g. a macrophage) - a type of white blood cell that carries out phagocytosis (engulfment of pathogens).

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1) A phagocyte recognises the antigens on a pathogen as foreign.

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2) The cytoplasm moves around the pathogen, engulfing it.

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3) Lysosomes fuse with the phagocytic vacuole breaking down the pathogen.

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4) The phagocyte presents the antigens on its surface.

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The Immune Response - 2

T Lymphocyte - another type of white blood cell covered in receptors, each one with different receptors.

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1) Their receptors bind to complementary antigens presented by the phagocytes.

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2) This activates the T Lymphocyte to divide and differentiate to carry out different functions.

  • some release substances to activate B lymphocytes
  • some attach to antigens on a pathogen and kill the cell
  • some become memory cells
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The Immune Response - 3

B Lymphocytes - another type of white blood cell, covered in proteins called antibodies.

1) the antibodies bind to antigens to form antigen-antibody complexes. 

2 ) this activates the B lymphocyte to divide by mitosis into:

  • plasma cells
  • memory cells
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Plasma Cells

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Plasma Cells

-clones of B lymphocytes

-secrete lots of the antibodies specific to the antigen into the blood

-anitbodies bind to form antigen-antibody complexes:

  • variable region form the antigen binding sites - the shape differs to complement the antigen.
  • hinge region allows flexibility when the antigen binds.
  • constant region allows binding by antigens to immune system cells.
  • Disulfide Bridges hold the polypeptide chains together
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Antibodies

Antibodies help to clear an infection by:

Agglutinating Pathogens: each antibody has two binding sites so the pathogen can phagocytose a lot of pathogens all at once.

Neutralising Toxins: antibodies can bind to the toxins produced by pathogens preventing them form harming human cells by neutralising them. The toxin-antibody complexes are phagocytosed.

Preventing the pathogen binding to human cells: when antibodies bind to antigen they can block the cell surface receptors to prevent them binding with host cells.

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Memory Cells

Primary Response

- slow as there aren't many B Lymphocytes they can make the antibody.

- the B lymphocytes will produce the right antibosy but the person will show symptoms.

-after being exposed to an antigen the T and B Lymphocytes will produce memory cells which will stay in the body

- the cells will record the specific antibodies needed tobind to the antigen

...the person is now immune as their immune system has the ability to respond quickly to a second infection.

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Immunity

Active Immunity

This is when your immune system makes its own antibodies after being stimulated by an antigen.

  • Natural: when you become immune after catching a disease
  • Artificial: when you become immune after having a vaccination of a dose of antigens.

Passive Immunity

This is when you become immune after being given antibodies made by a different organism and your immune system doesn't produce any antibodies of its own.

  • Natural: when a baby becomes immune due to the antibodies it receives from its mother via the placenta and breast feeding.
  • Artificial: when you become immune after being injected antibodies from someone else.
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Vaccinations - help your body produce memory cells as it contains antigens.

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Herd Vaccination - when a lot of people in a community have been vaccinated against an infection, the people who haven't been vaccinated are unlikely to get the infection as there are less people to catch it off.

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Influenza

-proteins on the surface of the influenza virus act as antigens triggering the immune system

-these antigens can change regularly forming new strains of the virus

-memory cells will not recognise new strains

-hence a new vaccine is made

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Sources of Medicines Need Protecting

-many medicinal drugs are manufactured using natural compounds found in plants, animal and microorganisms.

-only a small number of organisms have been investigated s far so it's possible that plants or microorganisms exist that could contain compounds that could be used to treat currently incurable diseases.

- possible sources of drugs need to be protected by maintaining biodiversity. Else a specie could die out before we get chance to study them.

- organisms that have been already studied could still prove to be useful sources of medicines as new techniques are developed for identifying, purifying and testing compounds.

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