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Chapter 24 – The Body’s Defenses against Pathogens
State Standards Standard 10.a. – Standard 10.b. – Standard 10.c. – Standard 10.d. – Standard 10.e. – Pathogens Pathogens are • They are usually microorganisms
- Viruses – cold, influenza, HIV, SARS
- Bacteria – E. coli, stomach ulcers, strep throat, MRSA
- Parasites – trichinosis, round worm, tapeworm
• Bacteria and viruses are everywhere in nature, but
Pathogenic Bacteria • Some bacteria damage the body’s cells and tissues by breaking down the cells for food. • Other bacteria release toxins (poisons) that travel throughout the body interfering with the
Pathogenic Viruses • Viruses can attack and destroy certain cells in the body, causing symptoms of the disease. • Other viruses cause infected cells to change patterns of cell/tissue growth and development. Everyday steps to protect your health • Cover your nose and mouth with a tissue when you cough or sneeze. Throw tissue in the
• Wash your hands often with soap and water. Alcohol based hand cleaners are also
• Avoid touching your eyes, nose or mouth. Germs spread this way. • Try to avoid close contact with sick people. • Cook food thoroughly. Preventing Infections • Sterilization (medical, tattoo, piercing equipment) • Disinfectants/Antiseptics (bleach, “Lysol” type cleaners)
- Useful in decontaminating surfaces with which the body may come into contact
• Food processing (canning and packaging hygenically)
Treating Bacterial Infections - Antibiotics
• Chemicals that inhibit (slow/stop) the growth of bacteria
• Function by
- slowing the growth rate of the population giving the body’s defenses time to fight the
bacteria • Effective in treating bacterial infections only • Ex: penicillin interferes with the growth of bacterial cell walls
Also work by • Destroying bacterial cell walls (lysozyme) • Inhibiting the bacteria from synthesizing DNA, RNA, or proteins (erythromycin,
• Why doesn’t penicillin affect your cells? • Why doesn’t penicillin affect a virus infection? Antibiotic Resistance • When a strain of bacteria is exposed to an antibiotic
- the bacteria that are susceptible to the antibiotic die.
Complication: Antibiotics also kill beneficial bacteria (that live on and in you) that normally keep the harmful strains in check. The Body’s Defenses Nonspecific defenses against infection • The body’s first lines of defense against pathogens are nonspecific
Nonspecific Defenses – 1st line of defense Skin • Outer layer is a barrier of dead cells that most bacteria and viruses can’t penetrate. • Acids in sweat and oils • Sweat contains lysozyme that attacks cell walls of bacteria. (Found in saliva and tears, too) Digestive system Stomach acid kills most bacteria swallowed in food
Respiratory system • Hairs in nostrils
• Mucus in respiratory tubes trap microorganisms • Cilia sweep
Nonspecific defenses – 2nd line of defense – internal defenses
Internal defenses • When an invader penetrates the body’s external barriers, a set of nonspecific internal
defenses that depend mostly on white blood cells acts as a second line of defense.
2nd line of nonspecific defenses - WBC Types of white blood cells (WBC) • Macrophages – large cells that move in the interstitial fluid and “eat” any bacteria and
virus-infected cell they come in contact with
• Natural killer cells – attack cancer cells and infected body cells Chemical Warfare 1. Interferons Virus infects cell & then the infected cell produces and releases interferon molecules to warn neighboring cells of viral infection Interferon binds to healthy cell, -What do you think happens when virus tries to infect this cell ? 2. Complement Proteins • Found in blood in inactive form. • Activated by • Make microbes easier to engulf by macrophages. • Or cut lethal holes in membranes of microbes. Inflammatory response – nonspecific response to injury
• Widespread due to severe tissue damage or infection • Increase in the number of white blood cells • Cells release Pyrogens (“firemakers”), chemicals that tell your brain’s thermostat to turn up
• Causing a fever! • Will this reduce viral replication or bacterial growth? The Lymphatic System • The lymphatic system is a network of lymphatic vessels and organs • It returns tissue fluid to the circulatory system • It
• Lymph nodes can become infected during this war
Lymph nodes are key sites for fighting infection • They are packed with
Specific defenses – the immune system The Immune System • Recognizes and defends against invading microbes and cancer cells • When detects an antigen increases the number of cells that either
- Produce defensive proteins, antibodies
Specific Defenses – the immune system The immune system • Has
- remembers antigens it has been exposed to
- reacts against the antigens more quickly and more vigorously
Recognizing the Invaders - lymphocytes Lymphocytes • are white blood cells found most often in the lymphatic system • produce the immune response • originate from •
Human body has 2 trillion WBC produced by stem cells in bone marrow
Two kinds of lymphocytes carry out the immune response
The Cell mediated immune response • In the cell-mediated immune response T cells fight pathogens that have
Helper T cells • help activate cytotoxic T cells and macrophages • stimulate B cells Cytotoxic T cells • Attack body cells • Cytotoxic T cells are the only T cells that actually kill other cells • Cytotoxic T cells may attack cancer cells • The surface molecules of cancer cells are altered by disease Humoral Immune response •
B cells secrete specific antibody proteins as a form of defense against given identified antigen*.
*antigen could be from the surface of a cancer cell, virus, bacteria, or other pathogen… Antibodies mark antigens for elimination Antibodies • Bind to a certain antigen that triggers mechanisms to neutralize or destroy the invaders by 1. Blocking harmful antigens on microbes 2. Clumping bacteria or viruses together 3. Precipitating dissolved antigens 4. Activating complement proteins Immunity Immunity is Passive immunity – Antibodies produced by another animal are transferred to you • Mother to child: before birth + by breast milk • If bitten by rabid animal, treatment injection of antibodies against rabies Active immunity – Exposed to a pathogen which triggers the immune response and the development of Memory B cells • Developing active immunity by…
• Get vaccinated (weakened form of pathogen) • More than 20 different vaccines available today Immune response has memory • In the primary immune response,
- These cells may give the person lifelong immunity
• Remembers antigens it has been exposed to • Reacts against the antigens more quickly and more vigorously Primary Immune Response • Occurs when lymphocytes are first exposed to an antigen
• Antibodies are produced by B cells • Usually takes several days Secondary Immune Response • Occurs when exposed to same antigen again • Immune response is • Memory cells divide quickly producing a large number of lymphocytes that attack the
• (Ex: Sabin vaccine used against polio) • Causes the primary immune response • Produces
• When person exposed to actual antigen, secondary immune response occurs • Person
Immunodeficiency diseases • Immune components are lacking, and infections recur. • May arise
-SCID: Severe combined immunodeficiency (lack T& B cells)
HIV/AIDS Transmission of HIV • HIV is not transmitted through
• HIV can ONLY be transmitted through the exchange of
How HIV replicates in helper T cell 1. Viral envelope fuses w/ plasma membrane. Virus disassembles 2. HIV’s Reverse transcriptase enzyme copies RNA Genome into DNA 3. Double stranded DNA from new DNA 4. HIV’s DNA inserted into cell’s nuclear DNA (lytic or lysogenic cycle?) 5. Provirus DNA transcribed into RNA 6. Viral RNA translated into viral proteins (capsomeres and enzymes) 7. New HIV viruses assembled 8. New HIV viruses released * • Why are T cells important to your immune system? Can AIDS Be Cured?
• Scientists have no vaccine yet! Why? The high mutation rate of the retrovirus genome is
• The virus can be controlled by expensive multidrug antiviral “cocktails” that fight the
• How can new HIV infections be avoided?
• The only no-risk behavior with respect to HIV and AIDS is
• People who share contaminated needles to inject themselves with drugs are at a high risk
• People who have sex with IV drug abusers are also at high risk. Rating the risk of transmission (H) High risk of HIV exposure
(N) No HIV exposure 1. Abstinence (NO sexual intercourse of ANY kind) 2. Unprotected sex of ANY kind 3. Sharing needles 4. Getting blood on yourself while helping an injured person 5. _______ Wearing Latex* gloves when helping a person who is bleeding *if person has latex allergy, can be substitute with polyurethane 6. Sexual intercourse between two UNINFECTED people who remain monogamous (no other partners) and NEITHER person shares needles. 7. Receiving a blood transfusion in the USA where all blood is tested for HIV. 8. An HIV positive mother breast feeding her baby. 9. Using a NEW LATEX condom or oral barrier during sexual intercourse. 10. Sexual intercourse between two people who remain monogamous (no other partners) AND one person shares needles.
Varicella Di cosa si tratta La varicella è una malattia infettiva virale, molto contagiosa, che lascia una protezione permanente (per cui, di regola, non ci si riammala una seconda volta). Il virus responsabile della malattia, tuttavia, non viene mai completamente debellato; va a localizzarsi nei gangli nervosi del midollo, dove può rimanere senza dare problemi anche per tutta la
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