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Transcript
Why do you get sick? How do you get better? What’s the best way for you to avoid getting sick in the first place? For years, people thought diseases were caused by curses, spirits, etc. In the nineteenth century, Louis Pasteur and Robert Koch concluded that infectious diseases were caused by microorganisms (germs) = the Germ Theory of Disease In the summer of 1975, many children in Lyme, CT developed a rare form of childhood arthritis Allen Steere realized the children developed their problems after having a skin rash from a deer tick bite Steere’s colleague, Dr. Burgdorfer, found an unusual spiralshaped bacterium in the ticks and the child patients Steere injected lab mice with the bacterium and they developed similar symptoms = Lyme Disease So, Lyme disease is caused by a bacterium Koch developed a series of guidelines to identify the microorganism that causes a specific disease 1. The pathogen should always be found in the body of a sick organism and should not be found in a healthy one. 2. The pathogen must be isolated and grown in the laboratory in pure culture. 3. When the purified pathogens are placed in a new host, they should cause the same disease that infected the original host. 4. The injected pathogen should be re-isolated from the second host and be identical to the original pathogen. Disease no longer seems unavoidable consequences, but now pathogens could be identified and diseases could be prevented or cured. Section 40-1 No pathogen Healthy mouse Suspected pathogen Dead mouse Injection of organisms from pure culture Healthy mouse Suspected pathogen The pathogen should always be found in the body of a sick organism and should not be found in a healthy one. Dead mouse Suspected pathogen grown in pure culture. The pathogen must be isolated and grown in the laboratory in a pure culture. Pathogen When purified pathogens are placed in a new host, they should cause the same disease that infected the host. Dead mouse The very same pathogen should be reisolated from the second host. And it should be the same as the original pathogen. Disease = any change, other than injury, that disrupts the normal functions of the body Diseases can be inherited (ex. Hemophilia) Diseases can be caused by materials in the environment (ex. Cigarette smoke) Diseases can be produced by agents (ex. Bacteria, viruses, fungi) = pathogens Pathogens = “sickness-makers” Diseases caused by pathogens = infectious diseases, because they enter, or infect, the body The human body provides great conditions for pathogenic growth You have many different microorganisms living in your body that are actually harmless or beneficial However, some microorganisms are dangerous Some bacteria break down body tissues and others release toxins (poisons) Some protists, fungi, and worms are parasites that live inside you and use up your nutrients or destroy blood/nerve cells Viruses are nonliving pathogens that use a host cell to make copies of the virus and destroy other cells Infectious diseases are spread From person to person: coughing, sneezing, or physical contact ▪ Common cold, mumps, measles, influenza, STDs (AIDS), meningitis, athlete’s foot Contaminated water and/or food ▪ Cholera, dysentery, E.coli infection, salmonellosis Vectors: infected animals (ticks/mosquitoes) ▪ Lyme disease, malaria, West Nile virus, rabies Section 40-1 Pathogen Types Viruses Bacteria Protists Worms Fungi Chicken pox Agent That Causes Disease Rhinovirus Two types (A, B), plus subtypes Varicella Measles Paramyxovirus Tuberculosis Mycobacterium tuberculosis Neisseria meningitidis Vibrio cholerae Clostridium tetani Trypanosoma Disease Common cold Influenza Meningitis Cholera Tetanus African sleeping sickness Malaria Amoebic dysentery Schistosomiasis Beef tapeworm Athlete’s foot Ringworm Plasmodium Entamoeba histolytica Schistosoma Taenia saginata Imperfect fungi Imperfect fungi Method of Transmission Airborne; direct contact with infected person Airborne; droplet infection; direct contact with infected person Airborne; direct contact with infected person Droplets in air; direct contact with secretions of infected person Droplets in air; contaminated milk and dairy products Direct contact with a carrier Contaminated drinking water Contaminated wound; usually puncture wound Spread by tsetse fly Spread by Anopheles mosquitoes Contaminated drinking water Freshwater streams and rice paddies Contaminated meat Contact with infected person Exchange of hats, combs, or athletic head gear with infected person Drugs have been developed to use against pathogens Antibiotics = chemicals that kill bacteria without harming the cells of humans or animals Penicillin = interferes with the synthesis of cells walls by Eubacteria (breaks down peptidoglycan in their cell walls) Streptomycin = interferes with bacterial growth by blocking protein synthesis in ribosomes Antivirals = inhibit the ability of viruses to invade cells or multiply inside cells A series of defenses that guard against diseases = body’s protection Nonspecific defenses = “walls” of the immune system keeping everything out Specific defenses = “security guards” identifying and inhibiting pathogens Skin = most important nonspecific defense Physical barrier Acidic environment on surface kills bacteria Mucus, sweat, tears and saliva Traps pathogens and removes them from the body by cilia or destroys them using the enzyme lysozyme, which breaks down cell walls Inflammatory response = reaction to tissue damage caused by injury or infection Blood vessels around wound expand, white blood cells enter infected tissue and phagocytes (special WBCs) engulf and destroy bacteria, tissue becomes swollen and painful, body temperature increases (fever) to slow pathogen growth and increase circulation and activity of WBCs Interferon = proteins that “interfere” with the virus Proteins released by virus-infected cells to help other cells resist viral infection by inhibiting viral protein synthesis, blocking viral replication Pathogen: any disease causing agent Ex. Fungus, Bacteria, Virus etc. A series of specific defenses that attack the pathogens = immune response Antigen = a substance that triggers the immune response (organic molecules on the surface of pathogens) Antigens are chemicals present on the surface of viruses, bacteria, pollen grains etc. Antibody = protein that helps destroy pathogens by binding to antigen and attracting phagocytes to engulf and destroy them Phagocytes = engulf bacteria with amoeboid motion Lymphocytes = involved in immune response B cells = produce antibodies or immunoglobins (secreted proteins specific to foreign molecules) Helper T cells = coordinate the immune response Killer T cells = directly kill cells that are infected with intracellular pathogens. Immunity against pathogens in the body fluids (blood/lymph) Immunity produced by lymphocytes (type of WBC) B lymphocytes (B cells) produce antibodies to mark pathogens and prevent future infections Immunity that relies on lymphocytes (cells) Killer T cells (cytotoxic T cells) can attack infected cells and destroy their cell membranes Killer T cells are what make organ transplants difficult, because they see the new organ as foreign and begin to attack it = rejection. Here, the smaller cytotoxic T cell or Tc (arrow) is attacking and killing a much larger virus-infected cell. The T cell will survive while the infected cell is destroyed. People that survived infectious diseases, never developed the same disease again Memory B and T cells remain capable of producing specific antibodies to that pathogen, ensuring the disease never gets a chance to develop again An immediate active immune response against the pathogen in a vaccine Vaccination = injection of a weakened or mild form of a pathogen to produce immunity Prevents serious human diseases by stimulating the immune system to create plasma cells capable of producing the specific antibodies for another possible infection Active Immunity lasts long term (permanent) Antibodies produced by other animals for a pathogen are injected into the bloodstream The antibodies will produce passive immunity against a pathogen as long as they remain in circulation (several weeks) Antibodies from the mother are passed to the fetus through the placenta or to the infant in the mother’s milk = maternal immunity The antibodies will produce passive immunity against most infectious diseases for the first few months of life or longer if breast-fed Although the immune system defends the body from potential pathogens, sometimes disorders occur The immune system may overreact to an antigen, producing discomfort or disease The cellular nature of the immune response is a potential weak point Overreaction of the immune system Allergies occur when antigens from allergens (pollen, dust, dust mites) bind to mast cells (type of immune cell common in nasal passages) Activated mast cells release chemicals = histamines, which increase the flow of blood and fluids to the surrounding area (sneezing, runny eyes/nose, etc) Antihistamines = drugs used to reduce allergy symptoms by counteracting the effects of histamines Asthma = allergic reaction where smooth muscle contractions reduce the size of air passageways in the lungs making breathing difficult The immune system has the ability to distinguish “self” from “nonself” The immune system makes a mistake and attacks the body’s own cells (“it attacks itself”) Juvenile-onset diabetes (immune system attacks insulin- producing cells in pancreas) Myasthenia gravis (attacks neuromuscular junctions) Multiple Sclerosis (destruction of myelin sheath – attacks nervous system) Lupus (attacks cells and tissues resulting in inflammation and tissue damage: heart, joints, skin, lungs, blood vessels, liver, kidneys and nervous system) Pathogens are spread from person to person by sexual contact Bacteria cause syphilis and gonorrhea Viruses cause hepatitis B, hepatitis C, genital herpes, and AIDS Acquired Immune Deficiency Syndrome (AIDS) = when cells of the immune system are weakened by infection Caused by HIV (human immunodeficiency virus) and spread by contact with body fluids (drug needles, unprotected sexual intercourse, breast milk, blood during birth, blood transfusions) HIV attaches and destroys most helper T cells, so body is more susceptible to infections People DO NOT die from HIV/AIDS, they die from the infections they get because the HIV virus has left their immune system unable to respond to the infections Section 40-3 Infection; Immune system eliminates most of HIV Symptoms, such as swollen lymph nodes, are few Loss of immune function more apparent; appearance of characteristic diseases such as yeast infections Almost total loss of cellular immunity; AIDS Relative HIV concentration T cell concentration Years There are many different types of drugs being used. Each drug has a different approach: Stop the virus from attaching to cells. Stop the virus from creating its protein coat. Stop the virus from replicating its genetic information. Doctors are now treating people with HIV with drug cocktails (several different drugs at the same time) These cocktails have dramatically increased the amount of time people are living with HIV and their quality of life – VERY expensive! The number of people with HIV/AIDS has been decreasing. Total population 2007: 6,625,000,000 Adults age 15-49 with HIV/AIDS, 2005 – 38 mill New HIV infections, 2005 – 4.9 mill, 2007 – 2.5 mill Adult HIV prevalence (%), 2005 - 1.1, 2007 – 0.8 Women age 15-49 with HIV/AIDS, 2005 – 17.5 mill Children with HIV/AIDS, 2005 – 2.3 mill, 2007 – 2.5 mill AIDS orphans (ages 0-17), 2003 – 15 mill AIDS deaths, 2005 – 3.1 mill, 2007 – 2.1 mill Source: http://hivinsite.ucsf.edu/global?page=cr-00-01 Viral RNA genome is converted to double-stranded DNA by a virally encoded reverse transcriptase that is present in the virus particle. Then the genome can be transcribed. Once the virus has infected the cell, two pathways are possible: the virus becomes latent and the infected cell continues to function the virus becomes active and replicates, and a large number of virus particles are liberated that can then infect other cells There are two types of HIV (HIV-1 and HIV-2) HIV differs from many viruses in that it has very high genetic variability. This diversity is a result of its fast replication cycle, with the generation of 109 to 1010 viruses every day, coupled with a high mutation rate. This leads to many variants of HIV in a single infected patient in the course of one day. This variability is compounded when a single cell is simultaneously infected by two or more different strains of HIV. Cells multiply uncontrollably and destroy healthy tissue Cancer begins when cells lose the ability to regulate cell growth and division Tumor: mass of growing tissue ▪ Benign: tumors that will not spread to surrounding tissue (non cancerous) ▪ Malignant: tumors that can spread to other tissues and organs invading and destroying tissue (cancerous) Metastasis: the spread of cancerous tumors beyond their original site to new places in the body As cancer cells spread, they absorb nutrients, block nerve connections, and prevent proper functioning, disrupting the body’s balance Cancer is caused by defects in the genes that regulate cell growth and division Inherited genes Viruses: interfere with cell cycle (mitosis) ▪ Ex. Human papilloma virus (HPV: an STD) can lead to cervical cancer or genital warts (non cancerous) Radiation: causes mutations in DNA ▪ Ex. X-rays, nuclear radiation, sunlight (UV Rays) Chemicals: cause mutations in DNA ▪ Carcinogens = chemicals that cause cancer ▪ Ex. Chloroform and benzene (industrial solvents used in production of drugs, plastics and synthetic rubber, small component in gasoline), cigarette smoke Prevention by protecting your DNA from agents that cause cancer (not smoking, balanced diet with regular exercise) Treatments Surgery: remove tumors to prevent spread of cancer ▪ Problem: cancerous tumors spread, so some cancerous cell may remain in the body forming new tumors Radiation therapy: destroy cancer cells ▪ Problem: also damages healthy cells in the vicinity and there is a limit to how much a person can have Drug therapy (chemotherapy): using chemicals to destroy cancer cells or just stop the growth of cancer cells ▪ Problem: also damages healthy cells, uncomfortable side-effects Section 40-4 The Study of Cancer includes a knowledge of Symptoms Causes which may include a including Tumor Viruses Malignant including Chemicals which may consist of which are classified as Benign Radiation Treatments X-rays Sunlight Surgery Nuclear radiation Drug therapy Radiation therapy Blood Type of Donor Blood Type of Recipient A B AB O A B AB O Unsuccessful transfusion Successful transfusion Prentice Hall Biology Presentation Pro, 2002 Blood Types (review) Humans: 4 Main types classified by their antigens Type A: Type B: Type AB: Type O: A antigens B antigens A & B antigens no antigens B antibodies A antibodies no antibodies A&B antibodies