Disease and Immunity

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  • Pathogens cause disease
  • Include; Bacteria, Fungi and Viruses

Pathogens can penetrate an organisms interface with the environment:

  • Gas-Exchange: -Breath in air containing pathogens, most get trapped in mucus lining in the lung epithelium. Cilia move mucus up trachea and out of mouth. -Some pathogens still able to reach alveoli, where they can invade cells and cause damage.
  • Digestive system: -Eat and drink food containing pathogens, most killed by acidic conditions in the stomach. -some may survive and pass into intestines where they can invade cells of gut wall.
  • Skin: -If skin is damaged, pathogens on surface of skin can enter bloodstream. -Bloodclots forming a scab prevents pathogens from entering, some may enter before.


  • Pathogens can also cause disease by producing toxins and damaging cells.
  • TOXINS; are realeased into body (can block nerve cells +cause muscle spasms)
  • CELL DAMAGE; -Reupture cells releasing nutrients -Break down nutrients inside for own use  -Replicate inside them, causing them to burst.








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Lifestyle can affect the risk of developing some diseases;

CORONARY HEART DISEASE; affects the heart, and is increased by...

  • Poor diet (high saturated fat or salt)
  • smoking
  • lack of exercise                          -All of these 3 cause high blood pressure
  • excessisve alcohol intake 

 CANCER; result of uncontrolled cell division, and is increased by...   

  •  Smoking (mouth and lung cancer)
  • excessive exposure to sunlight
  • excessive alcohol intake

If you change your lifestyle, it will be able to REDUCE THE RISK of contracting these diseases.

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Immune Responce Intro...

Antigens are molecules on the surce of cells. -when a pathogen invades the body, antigens on its surface are identified as foreign... activating an immune resonce:

 PHAGOCYTES ENGULF PATHOGENS; -A phagocyte is a white blood cell that carries out phagocytosis. Found in the blood and in tissues.

  • 1. Phagocyte Recognises antigens on pathogen as froeign.
  • 2. Cytoplasm of phagocyte moves around the pathogen, engulfing it
  • 3. Pathogen is now in a phagocytic vacuole
  • 4. Lysosome (organelle containing lysosomal enzymes) FUSES with phagocytic vacuole. enzymes break down the pathogen.
  • 5. Phagocyte PRESENTS the pathogens antigens- sticks antigens on its surface to activate other immune system cells 


  •  T-cells also white blood cell
  • Proteins on surface bind to antigens presented by phagocytes.. Activating the T-Cell
  • Different T-cells react in different ways: -some release activate B-Cells -Some attach to antigens on a pathogen and kill the cell
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Immune Responce Into continued...

  •  B- Cells also white blood cell
  • Covered in antibodies (Proteins that bind antigens to form antigen-antibody complex)
  • Each B-cell has a specific shaped antibody,complementary to different shaped antigens

1. when antibody on surface of B-Cell meets complementary shaped antigen, it binds to it   2. this together with substances released from T-Cells, activates B-Cells    3. Acctivated B-Cells divide into plasma cell.


  • Plasma cells identical to B-Cells (clones)
  • Secreate lots of antibody specific to the antigen
  • Functions Include:   -Coating pathogen making it easier for phagocyte to engulf   -coating pathogen preventing it from entering host cells   -binding to and neutralising toxins produced.
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Types of Immune Responce

  • Slower than non-specific responce
  • Targets specific pathogens  

CELLULAR: Highly specialised, targeting pathogens inside cells. This is carried out by T-Cells

HUMROAL: Targets pathogens in body fluids using antibodies, Carried out by B-Cells 

Antibody Structure

-Proteins made up of chain of amino acid monomers, linked by peptide bonds  - how specific an antibody is depends on its variable regions (each antibody has a different shaped variable region that is complementary to one specific antigen)  

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Primary and Secondary Responce

PRIMARY: - when a pathogen enters the body for the first time it activates an immune responce.       -This primary responce is slow, as there are no B-Cells that can make the antibody needed to bind to it.   -Eventually the body will make enough of the right antibody to overcome the infection. The infected person will start to show symptoms of disease.   -after being exposed to the antigen, both T-Cells and B-Cells produce memory cells that remain in the body for a long time.   -Memory cells remember a specific antigen. Memory B-Cells record specific antibodies needed to bind the antigen. This person is now immune.

SECONDARY: -When the same pathogen enters the body again, the immune system will produce a quicker, stronger immune responce.   -Memory B-Cells divide into plasma cells that produce the right antibody to the antigen.   -Memory T-Cells divide into the correct type of T-Cells to kill the cell carrying the antigen.   -Often gets rid of the pathogens before symptoms appear.

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Vaccines and Antibodies in Medicine

  • Vaccination can help avoid disease. -Vaccines contain antigens causing the body to produce memory cells against a particular pathogen, without causing disease.
  • Reduces the occurence of disease , Herd Immunity; even the people that are not vaccinated have less chance to catch the disease.
  • Vaccines always contain antigens -Can be FREE or attaches to a dead or attenuated pathogen
  • Can be injected or taken oraly. -However a disadvantage through taking it oraly is it could be broken down by enzymes in the gut or molecules of the vaccine will be too large to be absorbed into the blood.
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Antigenic Variability

  • Antigens on the surface of pathogens activate the primary response.
  • When infected the second time with the same pathogen the secondary response is acctivated
  • Pathogens can change the surface antigens shape -so when infected the 2nd time, the memory cells provided from the first infection won't recognise the different atigens. So the primary response has to take place.
  • This takes time, meaning you become ill again
  • This also makes it hard to develop vaccines


-Causes influenza (flu)                                                                                                                       -Proteins on the surface of the influenza virus act as antigens, triggering the immune system.   -These proteins can change regularly, forming a new strain.                                                         -Memory cells will not recognise these new strains                                                                           -so the primary response has to take place with every infection.

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Monocloonal Antibodies

  • Monoclonal antibodies are antibodies produced from a single group of geneticallt identical B-Cells.   -They are identical in structure.
  • Antibodies are very specific as their binding sites have a unique structure that only one particular antigen will fit into.
  • you can make antibodies bind to anything you want and they will only bind to that molecule.
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