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Primary defence

Immune Response- Response to an antigen. Involves lymphocytes / production of antibodies

Primary Defence- Prevention of pathogens from entering the body / blood.

Examples of primary defence-

Ears- ear wax / nasal hairs traps pathogens / parasite

Eyes/Nose/Mouth- lysozyme / tears / nasal secretions / saliva- kills bacteria / contains antibacterial agent- nasal hairs filter out pathogens

Stomach/Vagina- gastric juice / stomach acid / acid in vagina- low/acidic pH- kills, pathogens / parasite by denaturing essential enzymes

Respiratory System- mucous membranes / goblet cells produce mucus to trap pathogens / parasite cilia waft to remove pathogen / parasite laden mucus

Skin- physical barrier to prevent entry of microorganisms - Platelets cause blood clotting prevents pathogens / parasite entering bloodstream

Expulsive Reflexes- Coughing  / sneezing (expels pathogens from respiratory system) -  Vomiting / diarrhoea (expels pathogens from digestive system)

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Blood Clotting & Antibody

  • When a vessel gets damaged collagen fibres get exposed and platelets stick to them.
  • Leucocytes collect at the site and with the platelets release an enzyme called thrombokinase
  •  This enzyme turns the plasma protein prothrombin into thrombin
  •  Thrombin is an enzyme which hydrolyses fibrinogen into fibrin a long insoluble molecule
  •  Fibrin fibres trap red blood cells & platelets  which dry to for a clot
  •  Calcium ions  are required throughout this whole process

Q. Name and describe the function of each component of an antibody.

  • Hinge region- Allows flexibility for bonding of more than one antigen
  • Constant region- Attachment to phagocyte
  • Variable region- Attachment to antigens
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Key words

Immune Response- Response to an antigen, Involves lymphocytes / production of antibodies

Antigen- A molecule that can stimulate an immune response. E.g. proteins and glycoproteins.

B lymphocytes- form part of cellular response to pathogens, mature in bone marrow, produce antibodies, undergo clonal expansion

T lymphocytes- form part of cellular response to pathogens, mature in thymus, secrete substances which kill infected cells, undergo clonal expansion, activate other lymphocytes

Autoimmune disorder- Immune system attacks own body cells, Normally B & T lymphocytes with receptors complimentary in shape to our own cell antigens are destroyed.

Antibiotic- Naturally occurring substance – produced by fungi and bacteria, Destroys bacteria, Prevents protein synthesis/ inhibit cell wall synthesis

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Secondary defence

Non-specific immunity- Phagocytes able to digest / break down a range of different pathogens

There are two types of phagocytes that you need to know about: neutrophils and macrophages.  These are responsible for killing any pathogens that pass the primary defences before they reproduce and cause the symptoms of disease.

Neutrophil                            Macrophages


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Neutrophil and Macrophage

Smaller- Relative size- Larger

Bone marrow- Location of production- Bone Marrow

Blood- Transport around the body- Blood

Blood and squeeze out into tissue fluid-Location of action- Blood,where they are called monocytes. Organs (e.g. lymph nodes)  where they develop into macrophages

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Action of phagocytes

1- phagocyte binds pathogen, receptor on phagocyte attaches to / recognises antigen on bacterium

2- pathogen engulfed by cytoplasm / plasma membrane of phagocyte, endocytosis / phagocytosis

3- formation of phagosome / phagocytic vacuole

4- lysosomes move towards and fuse with phagosome / phagocytic vacuole, release (hydrolytic) enzymes / hydrogen peroxide / free radicals into phagosome/ phagocytic vacuole

5- pathogen digested / broken down / hydrolysed, into amino acids / sugars / glucose / fatty acids / glycerol, useful products are absorbed into cytoplasm , by diffusion / active transport

6- Waste products are removed by exocytosis


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Q. Explain how phagocytes are able to pass from the blood to the tissue fluid.

 lobed nucleus so cells can change shape and can squeeze between cells and through pores in walls of capillaries. histamine makes capillary walls  leaky.

Infected cells release chemicals such as histamine, which attracts neutrophils to the area as well as making capillaries more leaky.  This causes more fluid to leave the capillaries at the site of infection causing swelling and redness.  This also causes more fluid to enter the lymph vessels and lymphatic system which leads the pathogen towards the macrophages in the lymph nodes.

Agglutinatin- Some antibodies have many y-shaped molecules stuck together, therefore many antigen binding sites. Each attaches to many pathogens at same time and sticks them together so they are too large to enter host cell.

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Specific immune response

The macrophages play an important role in initiating the specific response to a pathogen.

The cells in our bodies contain glycoproteins which are recognised by the immune system as non-foreign antigens.  This means that an immune response is not initiated.  Transplant patients have to suppress immunity using immunosuppressant drugs in order for transplanted organs with different glycoprotein antigens to not be rejected by the immune system.  This can leave patients vulnerable to other pathogens.

Role of B-Lymphocyte

  • There are around 10 million B-Lymphocytes in your body each one has a specific receptor
  • Only the one with the receptor binds to the pathogens antigen. Clonal Selection
  • The B-Lymphocyte differentiates and proliferates into Memory cells and Plasma cells. Clonal expansion
  • Memory cells give immunological memory and Plasma cells produce antibody
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Neutralisation- The antigen on the surface of the pathogen may be used by the pathogen to bind to the host cell, when antibodies bind to this antigen the pathogen cannot bind to host cell.  Antibodies can also bind to toxins and prevent these from entering host cells.

Q. Outline the ways in which antibodies reduce the threat from pathogens.

 antibodies bind to antigens on pathogen

neutralisation- antibodies cover binding sites on pathogen / bind to toxins, prevent binding / entry to host cell

agglutination- clump / bind together many pathogens, clump too large to enter host cell / increase likelihood of being consumed by a phagocytes

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B- Lymphocytes

Q. Describe the actions of the B lymphocytes in the immune response.

  •  humoral response- B lymphocyte has antigen receptor / carries antibody on its surface  complementary to only one antigen
  • clonal selection- selection & activation of specific B lymphocyte by macrophages / antigen presenting cells, T helper cells, cytokines or/and interleukins
  • clonal expansion- selected cell divides by mitosis  B cells differentiate to form plasma cells which produce and secrete antibodies. antibodies are specific / complementary to the antigen
  • B cells form memory cells- which are long-lived and remain in the body providing immunological memory therefore providing a faster / stronger response to subsequent exposure of same antigen / pathogen.

Q. Describe how cytokine molecules can stimulate specific groups of B lymphocytes to divide.

  • cytokine molecule produced by some T lymphocytes
  • cytokine e.g. interleukin, receptor has a specific shape so fits into and binds to receptor on cell surface membrane of B lymphocyte.
  • receptor and cytokine have complementary shapes this activates clonal expansion by mitosis
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Types of immunity

There are four different types of immunity. They are classified by picking one word from ‘Group A’ and one from ‘Group B’ to describe the nature of the immunity gained, e.g. Artificial Passive Immunity

  •  Natural Immunity: The result of normal bodily processes.
  •  Artificial Immunity: The result of medical intervention.
  • Active Immunity: Involves a response from the Lymphocytes.
  • Passive Immunity: Involves only the phagocytes.
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General questions

Q. Which groups of people are vulnerable to the flu virus each year.  the elderly, ‘at risk’ children / young people, pregnant women, those with compromised immune systems, those with chronic diseases, health workers, poultry workers / pig farmers

 Q. Why does the flu vaccine need to be changed each year. different strains of the virus / virus mutates each year-new strains have different antigens- antibody produced needs to match new strain / antigen

 Q. Which groups of people should be immunised and why. patients with HIV+ / AIDS / transplant / chemotherapy-m weak immune system / cannot produce many antibodies------ pregnant women - foetus / embryo has undeveloped immune system, antibodies can cross placenta ---------health workers / people living and working close to outbreak likely to be at increased risk of disease-------those with chronic diseases- inability to withstand further disease / already being in poor health

 Q. Why are costly immunisation programmes considered worthwhile.

days lost at work have an effect on economy, costs more to deal with the ill people than the cost of vaccination, response to public opinion, health service unable to cope , eliminating a disease

 Q. Why do some people choose not to be immunised.-  too busy / can’t be bothered / feel it is unnecessary, lack of trust in government, media scare stories, concerned about side effects, allergic to vaccine , fear of needles,religious / cultural / ethical reasons

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Autoimmune Disease

An autoimmune disorder occurs when the body’s immune system attacks and destroys healthy body tissue by mistake. There are more than 80 types of autoimmune disorders.

When you have an autoimmune disorder, your immune system does not distinguish between healthy tissue and antigens.  As a result, the body sets off a reaction that destroys normal tissues.

The exact cause of autoimmune disorders is unknown. One theory is that some microorganisms (such as bacteria or viruses) or drugs may trigger changes that confuse the immune system.  This may happen more often in people who have genes that make them more prone to autoimmune disorders.

An autoimmune disorder may result in:

  • The destruction of body tissue
  • Abnormal growth of an organ
  • Changes in organ function
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New drugs

There are currently over 6000 different kinds of medicine available in the UK but more are continually needed because: 1-new diseases emerging, 2- diseases for which there is no effective treatment, 3- some antibiotic treatments becoming less effective

 There are five main ways in which new drugs are discovered:

1) accidental discovery – e.g. penicillin

2) traditional remedies – e.g. aspirin, morphine

3) observation of wildlife – e.g. monkeys rub citrus oil on their fur – antiseptic / insecticide

4) further plant research  - chemical fingerprinting technology

5) modern research – isolating active ingredients from traditional medicines/ gene sequencing/ molecular modelling

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  • Destroy pathogenic bacteria
  •  Reduce suffering and possible death from bacterial infections
  •  Increase productivity – animal rearing


  • Bacteria randomly mutate and may become resistant to antibiotic
  • Some strains of bacteria resistant to numerous different antibiotics
  • May eventually be unable to treat bacterial infections
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