The Immune System

1
The Immune System

• In this lesson, you will Learn About
• The function of the immune system.
• How antibodies protect the body from pathogens.
• How you can develop immunity to a disease.

2
The Immune System

• The Vocabulary terms in this lesson are
• Immune system.
• Inflammation.
• Lymphatic system.
• Lymphocytes.
• Antigens.
• Antibodies.
• Immunity.
• Vaccine.

3
Keeping Pathogens Out

Each day you are exposed to countless
pathogens. Your body can repel, trap, or destroy
most of these pathogens before they can do any
damage. The five major barriers against such
invaders help keep pathogens out.
4
The Five Major Barriers
5
The Immune Systems Nonspecific Response
If pathogens enter the body, the immune system
launches an attack. The immune systems
nonspecific response is always the same,
regardless of the type of foreign substance that
invades the body. The inflammatory response is a
nonspecific response that occurs if a foreign
invader gets past the five major barriers.
6
The Immune Systems Nonspecific Response (contd.)

• The steps of the inflammatory response
• The blood supply to the affected area increases,
  and circulation in that area slows down.
• This raises the blood pressure in the area,
  causing fluid to leak from the blood vessels.
• As a result, surrounding tissues swell.
• Special white blood cells called phagocytes
  attack the invading pathogens.
• The phagocytes surround the invaders, take them
  apart, and eat them.

7
The Immune Systems Nonspecific Response (contd.)

• Other components of the inflammatory response
• The phagocytes release special proteins to help
  defend the body. One of these proteins,
  interferon, stops viruses from reproducing and
  helps the cells that fight infection.
• If the infection has spread throughout the body,
  a fever becomes part of the inflammatory response.

8
Inflammation

• During the inflammatory response, more blood
  flows to the infected area, and phagocytes rush
  in to destroy the invading pathogens.

Phagocyte
Pathogen
Splinter
Pathogen
Phagocyte
Blood vessel
9
The Immune Systems Specific Responses

• When pathogens survive the inflammatory response,
  the body counters with a specific response. This
  response
• Is tailored to a particular pathogen and the
  poisons that it produces.
• Not only defends the body against an invading
  pathogen, but also allows the immune system to
  remember that particular type of pathogen.

10
The Lymphatic System
The lymphatic system is a secondary circulatory
system that helps your body fight pathogens and
maintain its fluid balance. Your body calls upon
the lymphatic system to fight against specific
pathogens.

11
The Lymphatic System (contd.)

• The lymphatic system circulates a watery fluid
  known as lymph.
• Special white blood cells in the lymph are called
  lymphocytes. There are three types
• B cells
• T cells
• NK cells

12
The Lymphatic System (contd.)

• The lymph also contains phagocytes called
  macrophages that digest and process the invading
  pathogens and then help the lymphocytes identify
  them.
• The three types of lymphocytes are activated when
  the body recognizes a part of a pathogen known as
  an antigen.

13
Antibodies
Your body reacts to antigens by producing
antibodies. Antibodies are proteins that attach
to antigens, keeping them from harming the
body. B cells produce specific antibodies to
fight a particular type of antigen.

14
The Immune Systems Response to Infection

1. A macrophage engulfs one of the pathogens and
   presents its antigens to the T cells, which
   identify the pathogen as an invader.

1. T cells multiply at the site of the infection.
   The T cells activate the B cells.

1. A pathogen invades the body. The antigens in the
   pathogen activate the immune systems response.

15
The Immune Systems Response to Infection
(contd.)

1. Memory T cells and B cells remain in the system.
   The next time this type of pathogen enters the
   system, these memory cells attack it swiftly.

1. B cells multiply.

• The B cells release antibodies, which attach
  themselves to the antigens. Special T
• cells attack and destroy the invaders.

1. Some B cells and T cells become memory cells.

16
Immunity

Your bodys ability to resist the pathogens that
cause a particular disease is called
immunity. You were born with some immunities
that were passed on to you from your mother.
These immunities lasted for a few months, after
which you began to produce antibodies on your own.
17
Immunity (contd.)

Another way your body builds immunity is by being
exposed to pathogens and by having certain
diseases. When your body encounters an antigen,
it produces memory B cells and T cells. Often
these memory cells stay in the blood. If the same
type of pathogen returns, the immune system
fights it so that you do not become ill a second
time.
18
Immunity (contd.)

You dont have to get a disease to acquire
immunity to it. You can receive an immunization,
or vaccine. This process is called immunization
because the antibodies your body produces in
response to the vaccine will build immunity.
19
Reviewing Terms and Facts

• Define the term immune system.

• The immune system is a combination of body
  defenses made up of cells, tissues, and organs
  that fight off pathogens.

20
Reviewing Terms and Facts

1. What are the bodys five major barriers against
   pathogens?

• Tears
• Saliva
• Skin
• Mucous membranes
• Stomach acid

21
Thinking Critically

1. Why do you think diseases that damage the immune
   system are so dangerous to the body?