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Playing Defense
The Body’s Defense System
External Defenses
•A pathogen is an organism, a virus, or a protein that
causes disease
•Your skin provides external protection against
pathogens that may enter the body
•Hair, nails, and sweat and oil glands help provide
protection
•Eyelashes and ear hair keep particles in the air from
entering the body
•Mucus in your nose and mouth wash pathogens
down into your stomach to be digested
Internal Defenses
•Sometimes, skin is cut and pathogens can enter the
body
•When this occurs, blood flow increases to the area
causing swelling and redness – this is called
inflammation
•The body temperature is raised – fever – this
response slows the growth of the bacteria or other
pathogen
•If these internal defenses don’t work, then the
immune system responds
The Immune System
• The immune system is made up of tissues and specialized white
blood cells that recognize and attack foreign substances in the
body
• White blood cells are able to move out of the blood vessels and
patrol all the tissues of the body
• There are three types of white blood cells: macrophage, T
cells, and B cells
• A macrophage is a white blood cell that destroys pathogens by
engulfing and digesting them
• Macrophages help start the body’s immune response to
antigens
• Antigens can be pathogens or any foreign material in the body
•Some T cells coordinate the body’s immune
response, while others attack infected cells
•Helper T cells activate other T cells, called killer T
cells
•Killer T cells attack infected body cells
•Helper T cells also activate B cells
•B cells make antibodies that attach to specific
antigens
•An antibody is a specialized protein that binds to a
specific antigen to tag it for destruction
Building Immunity
• The body builds immunity against a disease when it is exposed to the
pathogen that causes the disease
• Immunity is the ability to resist or recover from an infectious disease
• Immunity is passed from a mother to fetus
• Can result from the body being infected
• Can result from the body being vaccinated
• Once your body has fought a pathogen, the body produces memory
cells – these cells remember a certain pathogen
• Memory cell become activated when the pathogen enters the body
• Your body immediately starts to make many T cells and B cells to attack
• Memory cells make you immune to the pathogen
•A vaccine is a substance prepared from killed or
weakened pathogens that is introduced into the
body to produce immunity
•The vaccine stimulates the body to make an
immune response.
•B cells make antibodies to attack the specific
pathogen being injected
•Vaccines are used to trigger the body to make
memory cells for a certain pathogen without
causing illness
Challenges to the Immune System
• Allergies are an immune system’s reaction to foreign antigens that are not
dangerous to most people
• Can be caused by foods, medicines or types of pollen or mold
• Cancer is a group of diseases in which cells divide at an uncontrolled rate – the
immune system may not be able to stop the cancer cells
• Immune deficiency occurs when the immune system fails to develop or becomes
weakened
• For example, the AIDS virus infects the helper T cells – when the number of
helper T cells becomes low, neither the killer T cell nor the B cell immune
response can be activated
• A disease in which the immune system attacks the body’s own cells is called an
autoimmune disease
• For example, rheumatoid arthritis is a disease in which the immune system
attacks the joints of the body