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6.3 Defense against
Infectious Disease
6.3 Assessment Statements
• Define pathogen.
• Explain why antibiotics are effective against bacteria
but not against viruses.
• Outline the role of skin and mucous membranes in
defense against pathogens.
• Outline how phagocytic leucocytes ingest pathogens in
the blood and in body tissues.
• Distinguish between antigens and antibodies.
• Explain antibody production.
• Outline the effects of HIV on the immune system.
• Discuss the cause, transmission and social implications
of AIDS.
Define pathogen
• A pathogen is any living
organism or virus that is
capable of causing disease
• Ex: viruses, bacteria, fungi, and
various types of worms
Typically our bodies naturally
defend/fight off these
pathogens, but if they do not,
you may end up with
disease/infection
Why do antibiotics work against bacteria, but not
against viruses?
• Antibiotics are chemicals that take advantage of the
differences between prokaryotic cells (bacteria) and
eukaryotic cells (your cells)
– the antibiotics may block the bacteria's ability to synthesize
proteins or may inhibit the production of new cell walls,
blocking reproduction
• Viruses on the other hand invade our cells and use
them to multiply; therefore, any chemical that
would harm the virus would also harm our own
cells
Bacterial vs. Viral Infections
How to Prevent Pathogens from Entering our
Bodies
1. Skin – 2 layers; top “dead” layer is the
epidermis and the bottom “living” layer is
the dermis (serves as physical barrier against pathogens)
-
Top dead layer is a
good boundary
between pathogens and
our bodies as
long is it remains intact.
This is why we
need to clean and cover
any open wounds.
For the pathogens that enter
via our food or water:
2. Stomach acid – the very acidic
environment will help to kill
most of the ingested
pathogens
Preview Animation
For pathogens that
enter via the air:
3. Mucous Membranes –
cells that secrete this
sticky mucus can trap
pathogens and then
using cilia, can try to
remove the pathogens
from your body; also,
many of these cells also
secrete an enzyme
“lysozyme” that can
breakdown/damage the
pathogens
You need to
highlight 4 areas
that are protected
by mucous
membranes
Non-Specific Immune Response
(localized infection)
1. Neutrophils are attracted to site of inflammation –
begin phagocytosis
2. Macrophages move to infection – begin
phagocytosis
-
Phagocytosis – engulfing pathogen and break down
with enzymes
iPAD Assignment
Objective: In a group of 2-3, research your given
virus and create an informative slide with keynote
that details the following information on your virus:
– How is it contracted?
– What are the symptoms?
– Any available treatments/vaccinations?
– Include a visual aid of virus/infected person/etc.
– Any additional interesting information
Viruses for iPAD Assignment
1.
2.
3.
4.
5.
6.
7.
Measles
Smallpox
Rubella
Influenza
Polio
Rotavirus
Norovirus
8. Hepatitis B
9. Rabies
10. Rhinovirus
11. Herpes simplex type 2
12. Human Papillomavirus
Video: How the Flu Virus is Spread
• Antigen – a protein on the surface of a pathogen;
when a macrophage identifies one of these it
triggers your body’s immune response
• Antibody – protein molecules that we produce in
response to a specific type of antigen; produced by
B lymphocytes
• Antibodies are specific to just one type of antigen,
but their structures are similar
– Each one is a Y shaped protein
– At the end of each fork on the Y is a binding site where
the antibody can bind to an antigen
1.
2.
3.
4.
Specific Immune Response (Adaptive Immunity)
Macrophages identifies a pathogen via the antigen
Macrophage partially digests pathogen, but
displays part of it on its cell membrane (“antigen
presentation”) so that circulating leukocytes can
recognize and become activated
A specific antigen type is identified by leukocytes
called helper–T cells (this turns immune response
from non-specific to specific since the antigen is
now known)
Helper-T cells help activate specific B cells that can
produce an antibody to bind with antigen
5.
6.
7.
8.
Typical Immune Response Continued
B cell clones itself (mitosis) to increase numbers
The newly formed “army” begin antibody
production
Newly released antibodies circulate in the
bloodstream to find antigens they match (then
help destroy)
Some of the cloned B cells remain in the
bloodstream and provide immunity from a second
infection; these are called memory cells
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter24/animation__the_immune_response.html