1. Fighting Disease
Noadswood Science, 2016

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

3. 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

4. Pathogen Barriers
Complete the pathogen barriers worksheet

5. 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

6. 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

7. 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…

8. 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

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

10. 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

11. Phagocytes

12. 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

13. Lymphocytes

14. 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

15. 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

16. Antibodies

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

18. 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

19. 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