Disease 3.1.1 AQA Biology Study Guide

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  • Created on: 13-10-12 19:14
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Disease
Pathogens
o Pathogen comes from the Greek `pathos' meaning `suffering'
o They can be passed on from one person to another therefore the diseases they cause are called `infectious
diseases'.
o They are microorganisms.
For a microorganism to be a pathogen it must:
o Gain entry to the host
o Colonises tissues of the host
o Resist defences of the host
o Causes damage to host tissues
o If a pathogen enters the host and manages to colonise the tissues, it causes an infection
o Disease occurs when this infection leads to recognisable symptoms
Virulence
Extent to which the pathogen causes damage
The Human Host
o Why is the human body a perfect environment for breeding?
Warm, constant temperature
Near to neutral pH
Constant food and water supply
Transport system the provides oxygen and removes waste
Entry of Pathogens
They can enter through natural interfaces between the external and internal environment, where useful materials
are exchanged.
The skin:
o Thick, continuous, keratinised
o Effective barrier to infection
o Microorganisms do not readily adhere to it
o Surface cells are shed and washed regularly
o Sweat is acidic
o Lysozyme exists in tears (breaks down bacterial cell walls)
o Invasion occurs when the skin is broken
o Cuts and abrasions
o Skin conditions (eczema)
o Biting insects (mosquitoes, lice, fleas)
o Animal bites and scratches
Respiratory system:
o Mucus layer
o Cilia
o Phagocytic cells
o Influenza, tuberculosis, bronchitis
Digestive system
o Stomach acid
o Enzymes
o Typhoid, dysentery, cholera
Reproductive and urinary system
o Mucus
o Low pH

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AIDS, syphilis, gonorrhoea
Colonising the Host
o Pathogens need to fix themselves to the site of infection
o Physical modifications (protein spikes)
o Chemical means (adhesive substances)
o Once fixed, rapid multiplication occurs
o They then need to spread newly formed pathogens throughout the tissues and body
o They produce enzymes which enable cell penetration
o Can enter the lymphatic system via tissue fluid and enter the blood system
o Measles enters the respiratory system, then blood system, and ultimately affecting the skin and the…read more

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Diet
o Smoking
o Obesity
o Physical exercise
o Sunlight
Analysing and interpreting data
o Epidemiology ­ study of the number of cases and pattern of a disease, in order to prevent and control it.
o Retrospective studies ­ using data from the past
o Prospective studies ­ collecting data as it accumulates.
o More reliable when there are more people involved and data collected by independent institution.…read more

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