6.3 Defense against Infectious Disease

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

How viruses work

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) - 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 we breathe: 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

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 antigen 2.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 4.Helper-T cells help activate specific B cells that can produce an antibody to bind with antigen

Typical Immune Response Continued 5.B cell clones itself (mitosis) to increase numbers 6.The newly formed “army” begin antibody production 7.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

Day 2: Need to review and do HIV/AIDS stuff Using the last two assessment statements in 6.3 Defense against Infectious Disease (related to HIV/AIDS) outline that section in your notes and be prepared to discuss next class