Transcript Document
The Defence System
Chapter 38
Pathogens
Pathogens are disease causing
organisms
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
Reason
Skin
Secretes enzymes from the
sebaceous glands that kill
bacteria. It is a physical barrier
Lines breathing, reproductive &
digestive tracts, Its sticky & traps
pathogens before they enter the
body
Ingest pathogens
Mucous
membrane
Phagocytic WBC
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
Antigens
An antigen is a foreign molecule that
causes antibody production
Antigens are located on:
bacterial cell walls
viral coats
cancerous cells
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
Monocytes & Lymphocytes
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
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)
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
THE IMMUNE
RESPONSE
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
T- lymphocytes ( T-cells)
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
Recognise antigens from other white blood
cells
Enlarge and form clones
These stimulate the production of B -cells
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
Suppressor T-cells
Control ( suppress) the immune response
Memory Cells
Memory T- cells survive for life and
memorise the immune response
Induced Immunity
higher & ordinary level
Is the ability to resist disease caused by
infection
There are 2 types of induced immunity
1. Active immunity
2. Passive immunity
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
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)
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