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Chapter 21- Infectious Diseases
Infectious Diseases- diseases caused by organisms or viruses that enter & multiply within
the human body
Microorganisms- organisms so small that they can only be seen through a microscope.
Pathogens- microorganisms and viruses that cause disease
Bacteria-simple, single-celled microorganisms; live in air, soil, food and on the bodies of plants
and animals
Viruses- the smallest of all pathogens (they are about 100 times smaller than most bacteria
Fungi- organisms such as yeasts, molds and mushrooms
Protozoans- single-celled organisms that are much larger and more complex than bacteria
How Pathogens Are Spread
*Infected people
*Infected animals
*Contaminated objects
*Contaminated food, soil or water
Defenses Against Disease
Physical & Chemical Defenses: your body’s first line of defense against infectious disease
Skin- serves as a physical & chemical barrier; surface cells are hard & have no gaps
between them; sweat acts as a chemical barrier because it contains acids that
kill many bacteria
Mucus membranes- secrete a liquid called mucus; mucus traps many pathogens &
washes them away
Cilia- trap and remove pathogens
Saliva/tears- trap pathogens & washes them away
Digestive system- chemicals in your digestive system kill many pathogens; the normal
motion of the digestive system also moves pathogens out
Inflammation: second line of defense; inflammation is your body’s general response to all
kinds of injury, from cuts & scrapes to internal damage
Phagocytes- blood, other fluids and white blood cells that leak out of enlarged blood vessels
to engulf and destroy pathogens
Immune System: 3rd and most sophisticated line of defense against pathogens
Lymphocytes- white blood cells that carry out most of the immune system functions
Immunity- your body’s ability to destroy pathogens that it has previously encountered
before the pathogens are able to cause disease
T Cells- a type of lymphocytes that perform several functions
Killer T cells- destroy any body cell that has been infected by a pathogen
Helper T cells-produce chemicals that stimulate other T cells & B cells to fight off
infection
Suppressor T cells- produce chemicals that “turn off” other immune cell system cells
when an infection has been brought under control
B cells- lymphocytes that produce antibodies
Antibodies- proteins that attach to the surface of pathogens or to the toxins produced
by pathogens
Lymphatic system-network of vessels that collects fluid from your tissues and returns it
to your bloodstream
Passive Immunity- immunity acquired by receiving antibodies from a source other than one’s
own immune system
Active Immunity- immunity that results from either having a disease or from receiving a
vaccine
Immunizations- injections that cause you to become immune to a disease