BC SCIENCE 8 ~ UNIT
1
Cells and Systems
CHAPTER 3
The Immune System Protects the Human Body
CHAPTER 3.1
The Immune System (pp. 100-109)
The Components of Blood
(from Ch. 2. 3)
We learned about red blood cells when we were
studying the Respiratory & Circulatory systems.
There are several other components of blood that
have important roles in the immune system.
The Components of Blood
(from Ch. 2. 3)
• a drop of healthy blood contains about 5,000 –
11,000 white blood cells
• white blood cells are much larger in size than red
blood cells
• the number of white blood cells increases when
you have an infection
• white blood cells fight infection and prevent the
growth of cancer
The Components of Blood
(from Ch. 2. 3)
• in a drop of blood there are about 200,000 –
400,000 platelets
• platelets are important for clotting blood
• when you get a cut, platelets stop the bleeding
and seal the wound by thickening the blood so a
scab can form over the cut
Immune System
•
The immune system’s purpose is to
protect our cells from threats
• One type of threat is from pathogens,
which are “germs” or disease-causing
invaders
• These disease-causing organisms and
substances are everywhere and can infect
people with a range of infectious diseases
Methods of infection
There are many different ways to contract
infectious diseases. The majority of these
can be grouped into 4 categories.
Four ways to transmit infectious diseases
Transmission
Method
1. Direct Contact
Example
Shaking hands or sharing drinking
containers or bodily fluids with an
infected person.
Four ways to transmit infectious diseases
Four ways to transmit infectious diseases
Transmission
Method
1. Direct Contact
2. Indirect
Contact
Example
Shaking hands or sharing drinking
containers or bodily fluids with an
infected person.
Being near an infected person who sneezes
without covering his/her mouth. Pathogens
can travel up to 5 m and infect people within
that range.
Four ways to transmit infectious diseases
Four ways to transmit infectious diseases
Transmission
Method
1. Direct Contact
2. Indirect
Contact
3. Water and
Food
Example
Shaking hands or sharing drinking
containers or bodily fluids with an
infected person.
Being near an infected person who sneezes
without covering his/her mouth. Pathogens
can travel up to 5 m and infect people within
that range.
Eating foods such as eggs and some meats, that
are infected with Salmonella bacteria. Drinking
water infected with E. coli bacteria can also result
in serious illness.
Four ways to transmit infectious diseases
Four ways to transmit infectious diseases
Transmission
Method
1. Direct Contact
2. Indirect
Contact
3. Water and
Food
4. Animal Bites
Example
Shaking hands or sharing drinking
containers or bodily fluids with an
infected person.
Being near an infected person who sneezes
without covering his/her mouth. Pathogens
can travel up to 5 m and infect people within
that range.
Eating foods such as eggs and some meats, that
are infected with Salmonella bacteria. Drinking
water infected with E. coli bacteria can also result
in serious illness.
Being bitten by an animal carrying the
rabies virus.
Four ways to transmit infectious diseases
First Line of Defence
•
•
•
the first line of defence to infectious
diseases is the skin and the linings of all
internal body systems
the skin is a physical barrier that stops
most pathogens from entering the body
sweat and oil from your skin are slightly
acidic and also prevent some pathogens
from growing on the surface of our body
First Line of Defence
•
the mucus and
cilia lining your
nose prevent
pathogens from
entering your
respiratory
system
First Line of Defence
•
another defence is the
acidic gastric juice
secreted by the
stomach lining which
can destroy
pathogens such as
bacteria that enter the
stomach
Second Line of Defence
•
your body produces an immune response to
attack and destroy invaders that make it past
the first line of defence
•
this depends on your body’s ability to
distinguish between cells that belong to it and
cells that don’t
Second Line of Defence
•
the second line of defence includes two types
of immune response
1.
2.
an innate immune response - a response all animals
are born with
an acquired immune response - a response animals
with backbones can mount
The Second Line of Defense
Part 1: Innate Immune Response
Innate Immune Response
•
•
this response is quick
and general or nonspecific
the response is the
same for anything the
body recognizes as an
invader
Innate Immune Response
•
•
•
innate immune responses are mounted against
invading bacteria and some viruses (both are
pathogens)
the first action is inflammation, which is a flow
of fluid, cells, and dissolved substances from
the blood to the site of infection
this can cause a fever, swelling, and redness in
the area
Inflammation
Innate Immune Response
•
there is also an increase in types of white blood
cells called phagocytes which fight infection
•
these cells roam the body and search for invader
cells and swallow them
•
by increasing the number of phagocytes in an area
the immune system can destroy pathogens
Inflammation
The Second Line of Defense
Part 2: Acquired Immune Response
Acquired Immune Response
• this is a highly specific attack on a
particular pathogen or antigen
• an antigen is any substance the body
cannot recognize from a virus to a splinter
Pathogens and Antigens are
different:
• a pathogen is a disease-causing organism
or substance
• an antigen is a non-living particle or
substance (often part of a pathogen)
Acquired Immune Response
• acquired immune responses involve types
of white blood cells called B cells and T
cells
• this response can take up to a week to
develop because it needs time to develop
a specific response to defeat the
particular invader
B & T cells in action
• the process of an acquired immune
response begins when a white blood cell
(WBC) recognizes an antigen
• this WBC signals for other WBCs called T
cells which in turn signal B cells
B & T cells in action
• when B cells recognize antigens present in the
body they produce specific particles called
antibodies
• antibodies can attach to and destroy both
antigens and pathogens
In the figure below, a B cell has recognized the
antigens on this pathogen and produced
antibodies that bind to the antigens and
completely cover the pathogen.
B & T cells in action
• the antibodies either prevent the pathogen
from infecting body cells or mark it for
destruction by other white blood cells
• at the same time, the body produces large
numbers of similar B cells to fight other
antigens in the body
B & T cells in action
• once the attack is over, some antibodies
remain in the body to protect against
future infections - this protection is known
as immunity
B & T cells in action
• a second type of T
cell is called the
killer T cell
• these work
independently and
directly to destroy
antigens or
pathogens
Active Immunity
• all acquired immune responses help give
you active immunity
• this means your body remembers which
antibodies should be used to attack a
pathogen that has infected it before
• this is why people get diseases like
chickenpox only once
Active Immunity
• after the first infection, your body stores
some of the specific antibodies on B cells
• these memory B cells can be reactivated if
the antigen or pathogen reappears