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 Assignment1. Measles 8. Hepatitis B2. Smallpox 9. Rabies3. Rubella 10. Rhinovirus4. Influenza 11. Herpes simplex type 25. Polio 12. Human Papillomavirus6. Rotavirus7. Norovirus

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

Specific Immune Response (Adaptive Immunity)1. Macrophages identifies a pathogen via the antigen2. Macrophage partially digests pathogen, but

displays part of it on its cell membrane (“antigen presentation”) so that circulating leukocytes can recognize and become activated

3. 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)

4. Helper-T cells help activate specific B cells that can produce an antibody to bind with antigen

Typical Immune Response Continued5. B cell clones itself (mitosis) to increase numbers6. The newly formed “army” begin antibody

production7. Newly released antibodies circulate in the

bloodstream to find antigens they match (then help destroy)

8. 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