- basically the better version of this
- Lines of Defence
Hey there! Please be advised if you’re an boi this doesn’t exactly match your textbook! I’ve tried to keep similar concepts together so if you can’t find something, feel free to use the textbook, or use that neat little search bar up the top there! Thanks!
Disease can be sorted into two categories:
- Infectious - caused by pathogens (e.g bacteria, viruses, fungi) and are contagious
- Non-infectious - no pathogens and non-contagious
Pathogens are parasites that live in or on other organisms (the host) and have a harmful effect on their host. What bad guests! They can either me microscopic (invisible to the naked eye) or macroscopic (visible to the naked eye). Meet the pAtHoGeNs!
|Type of pathogen||Description||Typical size||Example of disease|
|Bacteria||Single celled organisms with DNA outside of the nucleus||0.2-5μm||Leprosy, throat infections, scarlet fever, HIV|
|Viruses||DNA or RNA wrapped in protein, requires a host to reproduce||20-300nm||AIDS, influenza, hepatitis, measles, salmonella|
|Protozoa||Single celled organisms with DNA inside the nucleus||2-200μm||Malaria, cryptospordium|
|Fungi||One or more cells with cell walls and a nucleus, but no chloroplast||50μm –> much larger||Ringworm, athlete’s foot|
Transmission can occur through direct contact, water, air, food, or other organisms (vectors). The table from BBC Bitesize below outlines some examples.
|Direct contact||This can be sexual contact during intercourse or non-sexual contact, like shaking hands.|
|Water||Dirty water can transmit many diseases, such as the cholera bacterium.|
|Air||When a person who is infected by the common cold sneezes, they can spray thousands of tiny droplets containing virus particles to infect others.|
|Unhygienic food preparation||Undercooked or reheated food can cause bacterial diseases like Escherichia coli which is a cause of food poisoning.|
|Vector||Any organism that can spread a disease is called a vector. Many farmers think tuberculosis in their cattle can be spread by badgers.|
There are also macroparasites and prions but this isn’t important for now.
|Type of disease||Description|
|Nutrition||Overeating, undereating, unbalanced diet|
|Ageing||Gradual breakdown of body tissues|
|Cancer||Multiplication of body cells at an abnormal rate|
|Inherited disorders||Passed on from family genes|
|Mental disorders||Caused by chemical deficiencies, strees, trauma|
|Metabolic disorders||Caused by chemical deficiencies|
|Environmental disorders||Exposure to poisons, asbestos, fire, drugs, pollution|
Most people die from lifestyle diseases such as cardiovascular diseases (stroke, heart attack) which is caused by obesity and lack of nutritione/exercise or lung cancer as a result of smoking.
Your body has many defences against pathogens. They can be either specific/non-specific. Specific defences involve targeted and tailored immunity of invading pathogens, while non-specific defences are applied to all threats equally.
The first line of defence are physical and chemical barriers that try to prevent entry of invading pathogens.
Physical barriers include:
- hairs and eyelashes
Chemical barriers include:
- stomach acid
If a pathogen evades the first line of defence, the second line of defence kicks in. At this point, an infection has occured.
- Affected area becomes swollen and inflamed, while body temperature increases
- More blood is directed to the area and blood vessels become permeable (porous - more leaky)
- White blood cells including phagocytes move to the infected area
- Phagocytes engulf and destroy pathogens
If a pathogen evades the first and second lines of defence, then the third line of defence kicks in. It is specific immunity; which is targeted and tailored towards the type of pathogen. Any foreign particle that stimulates the production of antibodies (usually through an immune response) is an antigen.
- Antigen enters body and lymphocytes (white blood cells) begin to divide. They split into specialised B lymphocytes and T lymphocytes (B cells and T cells respectively)
- B cells produce plasma cells which produce antibodies that bind with particular antigens. The first time the body is exposed to a specific type of antigen is a trial and error phase which takes 10-17 for the right antibodies to be produced
- T cells assist B cells to create an antibody and they do different jobs (e.g attack pathogens, attract/activate phagocytes, assist B cells with antibody production, etc)
Remember! Phagocytes are non-specific white blood cells, while lymphocytes are specific.