A&p Immune System

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Immune system: 2 mechanisms

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• Non specific defence – these protect against any of an enormous range of possible dangers
• Specific defence mechanism – immunity – Resistance is directed towards one particular invader. Immunological memory develops, which confers long term immunity to specific infections.

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Antigen

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Anything that stimulates an immune response

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4 main non specific defence mechanisms

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• Defence at body surfaces
• Phagocytosis
• Natural antimicrobial substances
• The inflammatory response

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Defence at body surfaces (3)

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- skin and mucous membranes
- Sebum and sweat (anti-microbial substances)
- Hair filter in nose – Cilia

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Phagocytosis – cell eating (4)

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• Macrophages and neutrophils are attracted to sites of inflammation and infection by chemotaxis
• Chemo – attractants are released by injured cells & invading microbes
• Non selective in their targets:
• Engulfing and digesting anything foreign

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Macrophages

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• Link between non specific and specific defence
• After digestion of an antigen they display the on there own cell surface to stimulate T- Lymphocytes and activate immune response

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Natural antimicrobial substances (6)

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• Hydrochloric acid
• Lysozyme (tears)
• Antibodies (sIgAs)
• Saliva (mechanical, acid)
• Interferons (secreted by T-lymphocytes which are infected by viruses:)
• Complement: Activated by immune complexes, helps to break them down

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Interferon

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• secreted by T-lymphocytes which are infected by viruses
• they prevent viral replication with in cells and spread of viruses to other cells

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Complement

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• System of about 20 proteins found in blood and tissues
• Activated by immune complexes (antigen & antibody bound together) & by foreign sugars found on bacterial cell walls
• Binds to & makes holes in bacterial cell walls: destroys the microbe
• Attracts phagocytic cells into an area of infection
• Binds to bacterial cell walls stimulating Phagocytosis

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Inflammation

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• Physiological response to tissue damage
• Its purpose is to: isolate, inactivate, and remove both the causative agent and damaged tissue so that healing can take place

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Causes of inflammation: (4)

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- microbes
- physical agents
- chemical agents
- antigens

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Signs of acute inflammation (5)

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- redness – rubor
- heat - calor
- pain - dolor
- swelling - tumor
- loss of function

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The inflammatory response (4)

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• Increased blood flow = more oxygen and nutrients - causes increased temperature & reddening of the area
• Release of chemical mediators like histamine – increased tissue fluid
• Increased permeability of small blood vessels – allow the movement of excess fluid and proteins (osmotic pressure of blood falls and water moves from the blood stream into the tissues)
• Migration of leukocytes (neutrophils for phagocytosis)

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Benefits of acute inflammation (5)

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• Promotion of Phagocytosis
• Promotion of the immune response
• Toxin dilution
• ↑ Core temperature
• Fibrin Formation

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Immune Cells

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• WBC manufactured in bone marrow
• Released into the blood stream to be processed into two types
• T Lymphocytes
• B Lymphocytes

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T Lymphocytes

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• Processed in the thymus
• Mature T Lymphocyte has been programmed to recognize only one type of antigen
• Directly attack antigen
• Provide cell mediated immunity

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B Lymphocytes

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• Processed in the bone marrow
• Mature in lymph organs
• Produce anti-bodies – targets one specific antigen
• Provide antibody mediated immunity

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Cell Mediated Immunity

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• Circulate in the body
• Antigen is presented to T Lymphocyte
• T cell colonial expansion into 3 types of cell
• Memory T Lymphocyte - long lived and provide immunity to the antigen
• Cytotoxic T- cells - bind to antigen and destroy it - cancer cells and infected cells
• Helper T-Cells – release cytokines to support cytotoxic t cells and stimulate b cells to produce antibodies

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Antibody Mediated Immunity

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• Fixed in lymph tissue
• Once antigen has been detected and bound expand into two cells
• Memory B Lymphocytes – long lived and provide immunity to the antigen
• Plasma Cells – Produce and release antibodies which bind to an antigen and destroy it

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Acquired immunity

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First antigen contact
• Primary response:
• After about 2 weeks low levels of antibodies
• Second antigen contact:
• Rapid response by memory b-cells

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Immunoglobulin G, or IgG

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works efficiently to coat microbes, speeding their uptake by other cells in the immune system.
produced mainly in secondary response. Present in the blood and tissue fluids, confers passive immunity to babies across the placenta and via the colostrum in breastfeeding. The immunity only lasts a few months. Has an antiviral and antibacterial action.

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IgM

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the largest which sits on the surface of B cells/ lymphocytes, before they convert to plasma cells, and is active in the early stages of immune response, neutralises viruses, and in combination with complement is especially bactericidal.

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IgD

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present on the B cells before transformation into plasma cells, concentration in blood very low, function uncertain, may assist T cells in their work

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IgE

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also known as reagin. Activity is mediated by mast cells, serum level is raised in worm and parasitic infestation, assists and promotes the histamine response, to increase permeability of blood vessel walls.

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IgA

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is contained in secretions such as tears, saliva, and from the mucosa of the gut, bronchi, bladder etc.