Pasteur & Koch came up with the germ theory of disease: infectious diseases occur when microorganisms cause physiological changes that disrupt normal body function – Can be caused by viruses, bacteria, fungi, protists and parasites – Except for parasites, all others known as pathogens

Koch’s Postulates: – 1. Pathogen must always be found in sick body but not healthy body – 2. Pathogen can be isolated & grown in lab – 3. If pathogen infects healthy host, should produce sickness – 4. Pathogen can be isolated from new host & looks identical

What’s the different between a symbiont and pathogen? – Symbionts are either harmless or beneficial – Pathogens destroy host cells, release poisons, block blood flow, and take up hosts nutrients

Diseases spread through coughing, sneezing, physical contact, exchange of body fluids, contaminated water/food/animals

Natural selection favors pathogens with adaptations that help them spread from host to host – Coughing, sneezing, body-to-body contact, sexual activity, drug usage, poor sanitation – Best way to avoid infection is to constantly wash your hands!

Those pathogens that thrive in both human and animal hosts are known as zoonosis – West Nile virus, Mad cow disease, Lyme disease, Ebola – Carriers of the disease who don’t get sick are known as vectors

Pg. 475 – 476 Q & A Work with a buddy – one sheet of paper for both of you!

Include skin, tears and other secretions, inflammatory response, interferon's and fever – First line of defense: skin, which is the most widespread defense

Pathogens can enter through the mouth, nose or eyes which are protected by saliva, mucus and tears – Contains lysozyme which breaks down bacterial cell walls – Stomach secretions (acid) also protect

Second line of defense includes inflammatory response, interferon's, and fever

Inflammatory response causes areas to become red and painful because of histamines (release by mast cells to increase flow of blood and fluids to the area) – White blood cells (phagocytes) will then engulf and destroy bacteria

Interferon's inhibit synthesis of viral proteins – Aka “interfere” with viral growth, slowing down the production of new viruses

Fever increases body temperature to slow down or stop the growth of some pathogens – Sometimes also speeds up several parts of the immune response

Specific defenses distinguish between “self” and “other” and inactivate / kill any foreign substance or cell that enters the body – Nonspecific = general threat – Specific = particular pathogen

Recognizes specific chemical markers on own cells – own secret password – If the marker is not recognized, will attack and remember it for later as “non-self” so that it can kill it quickly if it enters the body again: immune response

Antigens are any foreign substances that can stimulate an immune response – Found on the outer surface (the “flag”) – Immune responds by increasing # of cells to attack or produce proteins called antibodies

Antibodies tag antigens for destruction by immune cells (the “alert!!”) The shape of each antibody allows it to bind to only one antigen – very specific

Main working cells of the immune system are – B lymphocyte cells: grow and mature in red bone marrow; have antibodies on them; attack in body fluids – T lymphocyte cells: grow in red bone marrow but mature in thymus; have to be presented with antigen to attack