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The Defence System Chapter 38.

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Presentation on theme: "The Defence System Chapter 38."— Presentation transcript:

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


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

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