Defenses Against Disease If pathogens are everywhere, why aren’t you sick all of the time?
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Transcript of Defenses Against Disease If pathogens are everywhere, why aren’t you sick all of the time?
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Defenses Against Disease
If pathogens are everywhere, why aren’t you sick all of the time?
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When you do get sick, what keeps pathogens from multiplying until they take over your body?
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The Answer• Your body has a number of defenses against infection.
• Your body’s first line of defense against infectious disease includes both physical and chemical defenses that prevent pathogens from entering your body.
*see figure 21-3: Physical and Chemical Defenses
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Skin
• Your skin serves as both a physical and chemical barrier against pathogens.
• The surface cells are hard and have no gaps between them.
• Sweat acts as a chemical barrier because it contains acids that kill many bacteria.
• Old skin cells are shed constantly, and the pathogens on these cells are shed too.
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• In fact, microorganisms usually cannot get through your skin unless you have a cut, scrape, burn, or other injury.
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Mucous Membranes
Openings to your body, such as your
are covered by protective linings call mucous membranes. Mucous membranes secrete a fluid called mucous that traps pathogens and washes them away. Mucous also contains chemicals and specialized cells that attack pathogens.
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Cilia• Some of your body’s
mucous membranes are lined with tiny hair-like structures called cilia.
• Cilia and mucous help trap and remove pathogens.
• When you cough, sneeze, or blow your nose, the pathogens are removed along with the mucous.
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Saliva & Tears• Your saliva and tears can trap pathogens and
wash them away. Like mucous, saliva and tears also contain chemicals that attack pathogens.
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Digestive SystemChemicals in your digestive system, including your stomach, kill many pathogens.
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In addition, the normal motions of the digestive system not only move food through your system but also move pathogens out.
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Inflammation
• If pathogens are able to get past the physical and chemical defenses and to injure cells, your body is ready with a second line of defense- Inflammation.
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• Inflammation is your body’s general response to all kinds of injury, from cuts and scrapes to internal damage.
• Inflammation fights infection and promotes the healing process.
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Phagocytes• Within seconds after your body is injured, the damaged cells
release chemicals that cause blood vessels in the injured area to enlarge.
• Blood, other fluids, and white blood cells called phagocytes
leak out of the enlarged vessels.
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The phagocytes engulf and destroy pathogens.
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Meanwhile the infected area becomes red, swollen, and sore-in other words, inflamed.
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Healing• Phagocytes give off substances that cause
healing to begin. The fluids, phagocytes, and dead cells that accumulate at the injury cite often result in the formation of a thick, white liquid called pus.
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• Your body’s third line of defense against pathogens is your immune system.
• The immune system fights disease by producing a separate set of weapons for each kind of pathogen it encounters.
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When a pathogen enters your body for the first time, it often causes disease.
If your immune system is working, why does this happen?
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The Answer• Your immune system must build up its arsenal
of weapons against the newly encountered pathogen.
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• When a pathogen enters your body it takes time for it to multiply and cause disease.
• Once the immune system’s arsenal is built up, however, the immune system kills the pathogen, and your body gradually recovers.
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White blood cells called lymphocytes carry out most of the immune system’s functions.
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Immunity
• If your body as previously been attacked by a pathogen it will recognize it when it is exposed to it again.
• This time, your immune system will quickly recognize the pathogen and launch an immediate attack!
• When this happens you are said to be immune.
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• Immunity is your body’s ability to destroy pathogens that it has previously encountered before the pathogens are able to cause disease.
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Killer T Cells
• Killer T Cells destroy any body cell that has been infected by a pathogen.
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Helper T Cell
• Helper T Cells produce chemicals that stimulate other T cells and B cells to fight off infection.
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Suppressor T Cells
• Suppressor T cells produce chemicals that “turn off” other immune system cells when an infection has been brought under control.
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B Cells• B Cells produce antibodies. Antibodies are
proteins that attach to the surface of pathogens or to the toxins produced by pathogens.
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This binding action keeps the pathogen or toxin from harming the body.
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Once the infection is overcome, your B cells
stop producing antibodies, but they do not “forget”
how to produce
them.
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See Figure 5 for The Immune Response
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Passive vs Active Immunity
• There are two types of immunity-• 1. Passive• 2. Active
• Both types are important in protecting your body against defenses.
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Passive Immunity
• Immunity that is acquired by receiving antibodies from a source other than one’s own body.
• This type of immunity is temporary and not lifelong.
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Examples• It occurs naturally in babies who receive
antibodies from their mothers before birth.• After birth antibodies may also be passed to
an infant through the mother’s breast milk.
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Or
• When a doctor gives someone injections of rabies antibodies if they were bitten by a dog with rabies.
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Active Immunity• Active immunity is immunity that your own
immune system creates.• Active immunity results from either having a
disease or from receiving a vaccine.
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Vaccines
• Vaccines contain small amounts of dead or modified pathogens or their toxins.
• A vaccine causes your immune system to produce antibodies against a pathogen, as if you had actually been infected.
• You develop immunity without having to experience the disease.
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Booster Shots
• After a few years, you may receive a booster dose of some vaccines to “remind” your immune system to maintain your immunity.