Pathogens & Barriers
Pathogensvideo
Pathogens
A pathogen is a disease-causing organism
Pathogens are passed on from one host to another and therefore the diseases they cause are known as transmissible diseases
Pathogens can be passed on from host to host in different ways, including:
Direct contact - the pathogen is passed directly from one host to another by transfer of body fluids such as blood or semen (eg HIV, gonorrhoea, hepatitis B & C)
Indirect contact - the pathogen leaves the host and is carried in some way to another, uninfected individual
Methods of transmission table
Method of Transmission | Examples of diseases spread in this way |
Droplets in air | Common cold, influenza |
Food or water | Cholera, typhoid, dysentery |
Touching contaminated surfaces | Athlete's foot, Salmonella (can be transmitted on the feet of flies that land on food that then gets eaten) |
Insect bites | Malaria, dengue fever |
The Body Defences
The Body Defences
The body has several barriers to the entry of pathogens; these barriers can be either mechanical or chemical
Mechanical, or physical, barriers make it difficult for pathogens to get past them and into the body
Chemical barriers are substances produced by the body cells that trap or kill pathogens before they can get further into the body and cause disease
Examples of barriers to the entry of pathogens include:
Skin covers almost all parts of the body to prevent infection from pathogens; if it is cut or grazed, it immediately begins to heal itself, often by forming a scab
Mucus and hairs in the nose and airways make it difficult for pathogens to get past them and into the airways and lungs
Mucus traps pathogens
The hairs waft the mucus out of the airways
The stomach contains hydrochloric acid which is strong enough to kill any pathogens that are swallowed
Other examples include enzymes in tears, and sebum, an oily substance produced by the skin