Defending against infection
Pathogens are microorganisms
Bacteria release toxins
viruses damage our cells
White blood cells can ingest and destroy pathogens
White blood cells produce antibodies to destroy pathogens, and antitoxins to neutralise toxins.
Antibiotics are effective against bacteria, but not against viruses.
If too much antibiotics are taken you can become resistant to antibiotics.
Pathogens are microorganisms that cause infectious disease. Bacteria and viruses are the main pathogens.
Bacteria are living cells and, in favourable conditions, can multiply rapidly.
Diseases caused by bacteria include:
- food poisoning
- whooping cough
- gonorrhoea - a sexually transmitted disease
Functions of the white blood cells
White blood cells can:
- ingest pathogens and destroy them
- produce antibodies to destroy pathogens
- produce antitoxins that neutralise the toxins released by pathogens
- the pathogens are not the disease - they cause the disease
- white blood cells do not eat the pathogens - they ingest them
- antibodies and antitoxins are not living things - they are specialised proteins.
Viruses are many times smaller than bacteria.(smallest cell there is that consists of genetic material)
Viruses can only reproduce inside host cells, and they damage the cell when they do this.
Once a Virus gets inside a cell it can make 100's of copies of its self and keep reproducing.
-Eventually they will burst the cell and then the viruses are passed out in the bloodstream, the airways, or by other routes.
Diseases caused by viruses include:
- influenza - flu
- chicken pox
White blood cells called Phagocytes pass through the wall of the blood vessels and enter the surrounding tissue.Phagocytes move through the bodies tissues destroying pathogens and their toxins. Phagocytes can easily pass through blood vessel walls into the surrounding tissue and move towards pathogens or toxins
- ingest and absorb the pathogens or toxins
- release an enzyme to destroy them
Pathogens contain certain chemicals that are foreign to the body and are called antigens. Each lymphocyte carries a specific type of antibody
When a lymphocyte with the appropriate antibody meets the antigen, the lymphocyte reproduces quickly, and makes many copies of the antibody that neutralises the pathogen.
Antibodies neutralise pathogens in a number of ways:
- they bind to pathogens and damage or destroy them
- they coat pathogens, clumping them together so that they are easily ingested by phagocytes
- they bind to the pathogens and release chemical signals to attract more phagocytes
People can be immunised against a pathogen through vaccination. Different vaccines are needed for different pathogens.
Vaccination involves putting a small amount of an inactive form of a pathogen, or dead pathogen, into the body. Vaccines can contain:
- live pathogens treated to make them harmless
- harmless fragments of the pathogen
- toxins produced by pathogens
- dead pathogens
Antibiotics are substances that killbacteriaor stop their growth. They do not work againstviruses: it is difficult to develop drugs that kill viruses without also damaging the body’s tissues.
How some common antibiotics work
antibiotichow it works penicillin breaks down cell walls erythromycin stops protein synthesis neomycin stops protein synthesis vancomycin stops protein synthesis ciprofloxacin stops DNA replication