ch 7 cellular response in defence
Post on 21-Mar-2016
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Immunity – ability of the body to resist infection, or overcome an invading organism.
Immunity can be innate or acquired.
Innate immunity – inborn, unchanging, and non-specific.
Skin acts as a barrier.
Stomach acid kills pathogens.
Phagocytosis
• ‘cell – eating’
• foreign bodies are engulfed and destroyed
• phagocytic cells: monocytes and macrophages
• macrophages in connective tissue throughout body
• macrophages have many lysosomes with digestive enzymes
1.Macrophage detects bacterium and moves towards it.
2. Phagocytes engulfs bacterium in a vacuole by infolding of membrane.
3. Lysosomes fuse with vacuole.
4. Lysosomes release enzymes which digest bacterium.
5. Bacterium products absorbed by phagocyte.
*fig. 7.2 p.52*
• during infection, many phagocytes engulf many bacteria
• dead bacteria and phagocytes accumulate at injury site forming pus
• large number of immobile macrophages line liver, spleen and lymph nodes to remove foreign bodies from passing blood or lymph.
Acquired Immunity• natural or artificial
• it is gained by immune system producing antibodies in response to foreign antigens
Antigen – molecule recognised as foreign to body
• antigen markers on body cells known by immune system as ‘self’ antigens
• carried out by B and T-lymphocytes (white blood cells)
Naturally Acquired Immunity
B-cells • made in bone marrow, and pass to lymph nodes
• produce antibodies in response to foreign antigens
Receptor sites on antibodies specific to particular antigen.
• helper T-cells patrol body and activate B and T-cells when foreign antigen present.
• B-cells multiply rapidly
• some produce antibodies, some become memory cells
• receptor sites on antibodies join with foreign antigen rendering harmless
*see fig. 7.5 p.54*
• humoral response
T-cells (made in bone marrow, pass to thymus)
• when cell becomes infected by pathogen, pathogen’s antigens become present on cell membrane
• helper T-cells activate killer T-cells
• killer T-cells have specific receptors which join with foreign antigens
• killer T-cells release digestive enzymes to destroy infected cell.
*see fig. 7.4 p.53*
• cell-mediated response
• made in bone marrow, pass to thymus
Primary Response• person is infected by pathogen for first time
• latent period exists between antigen entering body, and antibodies being produced.
• memory B and T-cells produced
Secondary Response• on next exposure to antigen, memory cells are quickly stimulated to produce clones
•antibody production is faster, higher concentration, response lasts longer, often prevents disease. * Fig. 7.5 p.55*
Artificially Acquired Immunity• body is injected with harmless dose of foreign antigen
• induces Band T-cell production, and antibody formation
• also causes production of memory cells.
Vaccines• antigen can be harmless form (smallpox/cowpox), weakened (polio), dead (cholera), or chemically treated (attenuated) (tetanus).
Active (Acquired) Immunity• protection gained by person making antibodies
• natural or artificial
Passive Immunity• protection gained by person being given antibodies
• effects are short-lived
• natural or artificial
For each situation, say whether the immunity gained is passive/active, and natural/artificial.1.Person catching cold
2.Person given an injection of tetanus antibodies
3.Breastfeeding
4.A polio vaccine
Natural active
Artificial passive
Natural passive
Artificial active
Allergies
Allergic reaction – over-reaction of immune system to a harmless substance
• immune system produces antibodies, which connect with mast cells in connective tissue
• mast cells secrete histamine
• histamine causes runny nose, cough etc.
• relived by antihistamine drugs
* Fig. 7.6 p.57*
• all cells have antigen signature, any different antigens attacked by immune system
• transplanted tissues must be as close as possible or are rejected by immune system
Autoimmunity – immune system attacks own body cells, e.g.
1. Rheumatoid arthritis – cartilage in joints attacked
2. Multiple Sclerosis (MS) – myelin sheath around nerves attacked
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