Pathogens

• Certain symptoms caused by disease, either physical or mental.
• Malfunction of the body or mind which has an affect on good health.

• Gain entry to the host 
• Colonise the tissues of the host 
• Resist the defences of the host cell
• Cause damge to the host 

Pathogens include: Viruses, bacteria and fungi.

• If pathogens colonise a tissue it causes an infection
• A disease is caused when the infection leads to recognisable symptoms
• When the pathogen is trasferred from one individual to another is called transmission

• They get into the body by penetrating the organisms interfaces with the environment 
• An example of an interface is the skin, which forms a thick, continuous layer which acts as a barrier to infection
• The gas exchange system is also an interface, it has developed a mucus layer which is hard to penetrate 
• The digestive system allows food and water, which may contain pathogens, to be consumed. 
• The body produces enzymes to breakdown the pathogens and also produces stomach acid to kill microorganisms

• Damaging host tissues: the large number of pathogens can cause the surrounding tissues to not function properly, inhibit the synthesis of DNA or breakdown the membrane of the cells.
• Produce toxins: produce toxins which are harmful to the surrounding tissues.

• Pathogens, lifestyle and genetic factors can all cause disease.
• The faster a pathogen divides, the faster it can cause disease.