The Defence System Chapter 38 Pathogens l Pathogens

The Defence System Chapter 38

Pathogens l Pathogens are disease causing organisms l The human body has 2 ways of defending against pathogens 1. The GENERAL defence system 2. The SPECIFIC defence system

The General Defence System Acts as a barrier to pathogens entering the body Barrier Skin Reason 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

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

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

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

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

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

THE IMMUNE RESPONSE

l Plasma cells only live for a few days and most die off once infection is over l 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

T- lymphocytes ( T-cells) l l l 1. 2. 3. 4. 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

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

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

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

Induced Immunity higher & ordinary level l Is the ability to resist disease caused by infection l There are 2 types of induced immunity 1. Active immunity 2. Passive immunity

Active Immunity l Means the person produces his/her own antibodies in response to antigens l It is long term immunity l 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

Passive Immunity l Occurs when people are given antibodies to fight disease l They are not made by the person’s own immune system l 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)

Vaccination l 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 l IMMUNISATION Is a process that increases an organisms reaction to an antigen & therefore improves its ability to resist or overcome infection