Pathogens

Pathogens cause infectious disease.

• A pathogen is any organism that causes disease
• including microorganisms and larger organisms like tapeworms
• including bacteria some fungi and all viruses

Pathogens can pentrate an organisms interface with the enviroment

pathogens need to enter the body to cause disease.

1. GAS EXCHANGE- air can contain pathogens, most will be trapped in the mucus and be beated out by cillia to trachea and moiuth but some wil reach alveoli and invade cells.
2. SKIN - if you damage you skin pathogens on the surface can enter your blood stream. Blood clots can prevent pathogens from entering, some may enter before clot forms however.. 
3. DIGESTIVE SYSTEM - food and drink may contain pathogens. Most will be killed by the acidic conditions of the stomach , but some may live and invade the gut wall and cause disease.. 

PATHOGENS CAUSE DISEASE BY PRODUCING TOXINS AND DAMAGING CELLS

1. PRODUCTION OF TOXINS- many bacteria release toxins in to the body. for example: Tetanus produces a toxin that blocks the function of certain nerve cells- causing spasms
2. CELL DAMAGE- pathogens can physically damage host cells by: 

• RUPTURING them to release nutrients ( protiens) inside them
• BREAKING DOWN nutrients inside the cell for own use ( starving and nearly killing the cell
• REPLICATING inside the cells and bursting them with they are release ( like viruses)