Pathogens are disease causing microorganisms, that our body has many defence mechanisms against.
The skin is the first physical barrier, providing a protective layer that is hard to penetrate. We also have sebaceous glands that secrete acids, thus preventing the growth of pathogens.
Pathogens can enter through our mouth, nose and eyes quite easily. Saliva, mucus and tears contain lysozyme enzymes that break down the cell wall of many bacteria.
Our respiratory system then has it's own defences from nasal hair to mucus to enzymes.
Hydrochloric acid inside our stomach kills many harmful microorganisms that enter in our food and drink.
Our blood also has a great defence system; blood contains platelets and fibrin which causes blood to clot and scabs to form, sealing off cuts from the outside. Our blood also has another fantastic weapon; white blood cells. These can hunt down and destroy pathogens, they can ingest them, and they can neutralise the effect of the pathogen toxins on the body.