How the body fights disease

In a nutshell

Humans can take certain measures to reduce and prevent the spread of diseases. The human body will also provide protection against pathogens through chemical defences, physical barriers and the immune system.

Reducing disease spread

There are many ways to reduce and prevent the spread of infectious diseases. Some of these methods are outlined below.

Method	Description
Hygiene	Washing hands thoroughly before preparing food, and after sneezing or coughing can prevent the spread of disease.
Destroying vectors	Vectors are things that spread disease. For example, mosquitoes are vectors that spread malaria. Using insecticides or destroying their habitat means mosquitoes can no longer breed and spread disease.
Isolating people	Isolating people with an infectious disease can stop them from passing it on to other people.
Vaccination	Vaccinating people means they will be protected from the disease and they won't pass it on.
Condoms	A condom is a barrier method to prevent the spread of STIs.
Screening blood transfusions	Screening prevents the spread of STIs through blood.

Defences

The human body has chemical and physical defences that protect against pathogens. The chemical defences aim to kill the pathogen, whereas the physical defences aim to prevent pathogens from entering the body.

Chemical defences	Description
Lysozyme	An enzyme in tears, saliva and mucus that kills bacteria by digesting their cell walls.
Hydrochloric acid	The acid present in the stomach that kills pathogens in food and drink.

Biology; Health, disease and the development of medicines; KS4 Year 10; How the body fights disease

Physical defences	Description
Unbroken skin	This forms a protective barrier and prevents pathogens from getting through.
Mucus	(1.) Sticky mucus in the air passages and lungs traps pathogens. (2.) Cilia on the epithelial cells line the lungs and they move in a wave-like motion, moving the mucus towards the back of the throat where it is swallowed.

The immune system

If a pathogen does manage to enter the body, the immune system will act as the second line of defence and attack the pathogen. The immune system is mainly made up of two types of white blood cells called phagocytes and lymphocytes.

Phagocytes

Phagocytes (1.) are able to kill any pathogen so they are called non-specific. They bind to pathogens (2.) present in the blood. Their membrane surrounds the pathogen and engulfs it. Enzymes inside the phagocyte will then break down the pathogen. This process is called phagocytosis.

Biology; Health, disease and the development of medicines; KS4 Year 10; How the body fights disease

Lymphocytes

Lymphocytes are a type of white blood cell that recognise 'foreign' proteins on the surface of the pathogens.

Biology; Health, disease and the development of medicines; KS4 Year 10; How the body fights disease

1.	A new pathogen (shown in pink) infects a host cell. Lymphocytes (shown in blue) recognise 'foreign' proteins on the surface of the pathogens called antigens. They know that these proteins are 'foreign' as they are not naturally found in the body.
2.	The lymphocytes produce antibodies against these antigens. This can take between $1-3$ weeks so the person will start to feel unwell during this time.
3.	The antibodies bind to the antigens on the pathogen so they can be identified and destroyed by other white blood cells.

Typically, if the person is infected with the same pathogen again in the future, the white blood cells will recognise it quicker and produce antibodies faster. This means the person won't become ill from that pathogen and they are said to be immune.

Antitoxins

The body can also produce antitoxins that counteract/neutralise the toxins produced by the invading pathogen. The antibodies and antitoxins are specific to the antigen.