Diseases & Immunity
- Pathogen — Disease-causing organism
- Transmissible disease — A disease in which the pathogen can be passed from one host to another
- Antigen — Any substance foreign to the body that evokes an immune response. Found on the surface of pathogens.
- Antibody — Proteins that bind to antigens to destroy pathogens or marking of pathogens for destruction by phagocytes.
Ways a pathogen is transmitted:
- Direct contact (through blood & other bodily fluids)
- Contaminated food/water
- Air borne
- Vector (from animals)
Defences of body:
- Mechanical barrier - skin, hairs (e.g. nose hair)
- Chemical barrier - Mucus, stomach acid
- Cellular - white blood cells
How to control spread of disease:
- Clean water supply
- Hygienic food preparation
- Good personal hygiene
- Waste disposal
- Sewage treatment
Active and passive immunity
- Active immunity – The defence against a pathogen by antibody production in the body. It is gained after an infection by a pathogen or by vaccination.
- Passive immunity – A short-term defence against a pathogen by antibodies acquired from another individual, including across the placenta and in breast milk. Memory cells are not produced.
Vaccination process:
- Weakened pathogens or their antigens are put into the body.
- The antigens stimulate an immune response by lymphocytes which produce antibodies.
- Memory cells are produced that give long-term immunity.
Each pathogen has its own antigens, which have specific shapes. Specific antibodies have complementary shapes which fit specific antigens for detection
Cholera is a disease caused by a bacterium in contaminated water. The cholera bacterium produces a toxin that secretes chloride ions into the small intestine. Water moves into the gut by osmosis, causing diarrhoea, dehydration and loss of ions from the blood.