Presentation on theme: "Defenses Against Disease"— Presentation transcript:
1Defenses Against Disease If pathogens are everywhere, why aren’t you sick all of the time?
2When you do get sick, what keeps pathogens from multiplying until they take over your body?
3The 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
4SkinYour 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.
5In fact, microorganisms usually cannot get through your skin unless you have a cut, scrape, burn, or other injury.
6Mucous 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.
7CiliaSome 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.
8Saliva & TearsYour saliva and tears can trap pathogens and wash them away. Like mucous, saliva and tears also contain chemicals that attack pathogens.
9Digestive SystemChemicals in your digestive system, including your stomach, kill many pathogens.
10In addition, the normal motions of the digestive system not only move food through your system but also move pathogens out.
11InflammationIf 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.
12Inflammation 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.
13PhagocytesWithin 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.
15Meanwhile the infected area becomes red, swollen, and sore-in other words, inflamed.
16HealingPhagocytes 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.
17Your 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.
19When a pathogen enters your body for the first time, it often causes disease. If your immune system is working, why does this happen?
20The AnswerYour immune system must build up its arsenal of weapons against the newly encountered pathogen.
21When 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.
22White blood cells called lymphocytes carry out most of the immune system’s functions.
23ImmunityIf 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.
24Immunity is your body’s ability to destroy pathogens that it has previously encountered before the pathogens are able to cause disease.
25Killer T CellsKiller T Cells destroy any body cell that has been infected by a pathogen.
26Helper T CellHelper T Cells produce chemicals that stimulate other T cells and B cells to fight off infection.
27Suppressor T CellsSuppressor T cells produce chemicals that “turn off” other immune system cells when an infection has been brought under control.
28B CellsB Cells produce antibodies. Antibodies are proteins that attach to the surface of pathogens or to the toxins produced by pathogens.
29This binding action keeps the pathogen or toxin from harming the body.
30Once the infection is overcome, your B cells stop producing antibodies, but they do not “forget” how to produce them.
32Passive vs Active Immunity There are two types of immunity-1. Passive2. ActiveBoth types are important in protecting your body against defenses.
33Passive ImmunityImmunity that is acquired by receiving antibodies from a source other than one’s own body.This type of immunity is temporary and not lifelong.
34ExamplesIt 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.
35OrWhen a doctor gives someone injections of rabies antibodies if they were bitten by a dog with rabies.
36Active ImmunityActive immunity is immunity that your own immune system creates.Active immunity results from either having a disease or from receiving a vaccine.
37VaccinesVaccines 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.
38Booster ShotsAfter a few years, you may receive a booster dose of some vaccines to “remind” your immune system to maintain your immunity.