1. The Defence System
Chapter 38

2. Pathogens Pathogens are disease causing organisms
The human body has 2 ways of defending against pathogens
The GENERAL defence system
The SPECIFIC defence system

3. The General Defence System
Acts as a barrier to pathogens entering the body
Barrier
Reason
Skin
Secretes enzymes from the sebaceous glands that kill bacteria. It is a physical barrier
Mucous membrane
Lines breathing, reproductive & digestive tracts, Its sticky & traps pathogens before they enter the body
Phagocytic WBC
Ingest pathogens

4. Specific Defence System
This system is activated when pathogens get past the general defence system
Organs of the immune system that store WBC’s called lymphocytes and monocytes include the lymphatic vessels, tonsils, spleen lymph nodes

5. Antigens
An antigen is a foreign molecule that causes antibody production
Antigens are located on:
bacterial cell walls
viral coats
cancerous cells

6. Antibodies
An antibody is a protein produced by white blood cells in response to an antigen
Each type of antibody is highly specific to a single antigen
Antibodies inactivate antigens and allow them to be destroyed

7. Monocytes & Lymphocytes
Are WBC formed in the bone marrow
They engulf foreign bodies
They move into the lymphatic system eg lymph nodes, vessels ,spleen & thymus gland
LYMPHOCYTES:
WBC formed in the bone marrow
Move into lymphatic system--- produce antibodies
2 types – B cells & T cells

8. Advanced Study of Lymphocytes Higher Level Only
B – lymphocytes (B-cells)
Become active in the bone marrow
Each B cell produces only one type of antibody
When a B cell comes in contact with an antigen it divides into thousands of identical B cells ( called plasma cells)
These plasma cells produce antibodies that combine with and deactivate the antigen

9. THE IMMUNE RESPONSE

10. Plasma cells only live for a few days and most die off once infection is over
Some live on forever , these are called memory B –cells, if the same antigen enters the body again these B- cells produce more antibodies much faster than before, which prevents us being infected with the same antigen more than once

12. T- lymphocytes ( T-cells)
Become active in the thymus gland
Do not produce antibodies
Act in one of 4 ways
Helper T-cells
Killer T- cells
Suppressor T- cells
Memory T-cells

13. Helper T- cells Recognise antigens from other white blood cells
Enlarge and form clones
These stimulate the production of B -cells

14. Killer T-cells Destroy abnormal ( infected ) body cells
Recognise antigens on the surface of infected cells
They release proteins ( perforin) which form pores in the membrane of target cells
Water & ions flow in through these pores
Infected cells swell & burst

15. Suppressor T-cells Control ( suppress) the immune response
Memory Cells
Memory T- cells survive for life and memorise the immune response

16. Induced Immunity higher & ordinary level
Is the ability to resist disease caused by infection
There are 2 types of induced immunity
Active immunity
Passive immunity

17. Active Immunity
Means the person produces his/her own antibodies in response to antigens
It is long term immunity
It develops after a vaccination or an infection
(artificial) (natural)
Getting a vaccine
Pathogens are introduced into the body
Pathogens entering body in a natural manner eg getting a cold

18. Passive Immunity
Occurs when people are given antibodies to fight disease
They are not made by the person’s own immune system
It is short term immunity---eg. child getting antibodies naturally from its mother’s placenta or breastmilk (natural) OR getting and injection of foreign antibodies eg tetanus injection(artificial)

19. Vaccination
Is an injection of a killed pathogen in order to stimulate the immune system against the pathogen, thereby preventing the disease being suffered Eg. MMR, BCG
IMMUNISATION
Is a process that increases an organisms reaction to an antigen & therefore improves its ability to resist or overcome infection