Biology revision unit 1

- pathogens cause infectious diseases

- a pathogen is any organism that causes disease

- pathogens include, microrganisms and some larger organisms, such as tape worms.

- pthogenic microorganisms include, bacteria, fungi and viruses

- pathogens enter the body to cause disease, through an organisms surface of contact (interface) with the environment

gas exchange systems:

if you breath in air that contains pathogens most of them gat trapped in mucus.

this mucus lines the lungs epithelium.

-these also have cilia that beat and move the mucus upto the mouth where it is removed.

-some pathogens are able to reach the alveoli where they invade cells and cause damage.

skin :

if you damage your skin pathogens on the surface can enter the blood stream. the blood clots to stop pathogens entering the host but some get in before the blood clots.

digestive system:

if you eat food or drink something that contains pathogens, most will be killed by the acidity of the stomach.

however some may survive and enter the intestines where they can invade cells of the gut wall causing disease.

an example of this is cholera

production of toxins: many bacteria release toxins in to the body.

the bacterium that causes cholera produces a toxin that upsets the exchange of suvstances in and out of cells.

cell damage includes:

-rupturing them to release nutrients in to them

-breaking down nutrients in side the cell, this starves and kills the cell

-replicating inside the cell and bursting them when they are released

cholera bacteria produce a toxin that affects chloride ion exchange

1) the toxin causes chloride ion protien channels in the plasma membrane of the small intestine epithelial cells to open.

2) chloride ions move in to the small intestine lumen. the build up of cholera ions lowers the water potential of the lumen