Fighting Disease Noadswood Science, 2016

Fighting Disease Saturday, June 23, 2018 To describe how diseases are fought by the immune system

Precise Learning Students should be able to explain the role of the immune system in the defence against disease If a pathogen enters the body the immune system tries to destroy the pathogen. White blood cells help to defend against pathogens by: phagocytosis antibody production antitoxin production

Pathogen Barriers Complete the pathogen barriers worksheet

Pathogen Barriers Wax traps micro-organisms Tears contain an enzyme which kills micro-organisms Hairs and mucus stop micro-organisms from entering the body Saliva contains an enzyme which kills micro-organisms Blood contains white blood cells which kill any micro-organisms within the body Skin barrier stops micro-organisms from entering the body

Defence How does our body defend us from micro-organisms? The breathing organs produce mucus to cover the lining of these organs and trap the microbes The skin acts as a barrier If our skin is cut platelets seal the wound by clotting Our blood contains white blood cells

Passive & Active Defence The body has different ways of protecting itself against pathogens The first defence is passive immunity – aimed at stopping the pathogen getting into the body in the first place The body’s passive immunity system includes: - Skin Mucus and cilia (tiny hairs) in the respiratory system Acid in the stomach Enzymes in tears If a pathogen still manages to get into the body, the second defence takes over – this is called active immunity, and the white blood cells have key functions in this…

White Blood Cells White blood cells can: - Ingest pathogens and destroy them Produce antibodies to destroy pathogens Produce antitoxins that neutralise the toxins released by pathogens Pathogens are not the disease – they cause the disease! White blood cells ingest pathogens (they do not eat them!) known as phagocytosis

White Blood Cells There are several different types of white blood cells which engulf foreign cells and digest them

Phagocytes Phagocytes can easily pass through blood vessel walls into the surrounding tissue and move towards pathogens or toxins They then either ingest and absorb the pathogens or toxin; or release an enzyme to destroy them Having absorbed a pathogen, the phagocytes may also send out chemical messages that help nearby lymphocytes to identify the type of antibody needed to neutralise them

Phagocytes

Lymphocytes Pathogens contain certain chemicals that are foreign to the body and are called antigens Each lymphocyte carries a specific type of antibody - a protein that has a chemical 'fit' to a certain antigen When a lymphocyte with the appropriate antibody meets the antigen, the lymphocyte reproduces quickly, and makes many copies of the antibody that neutralises the pathogen Pathogen (coated in antigens) Antibodies attach White blood cell

Lymphocytes

Antibodies Antibodies neutralise pathogens in a number of ways: - They bind to pathogens and damage or destroy them They coat pathogens, clumping them together so that they are easily ingested by phagocytes They bind to the pathogens and release chemical signals to attract more phagocytes Lymphocytes may also release antitoxins that stick to the appropriate toxin stopping it damaging the body

Antibodies Step 1 – the white blood cell identifies the pathogen Step 2 – antibodies produced to ‘fit’ the pathogen Step 3 – antibodies fit the pathogen, ‘clumping’ them Step 4 – the white blood cell ingests the pathogen

Antibodies

Antitoxins Antitoxins are produced by the white blood cells which counteract toxins produced by invading bacteria

Practice Questions Give two ways in which the skin helps to defend the body against disease Give three ways in which white blood cells help to defend the body against disease

Answers Give two ways in which the skin helps to defend the body against disease – it acts as a barrier to pathogens, secreting antimicrobial substances Give three ways in which white blood cells help to defend the body against disease – consume pathogens (phagocytosis), produce antibodies and produce antitoxins