The Immune System and Disease

1. The Immune System and Disease Chapter 40

2. What is a disease? • A disease is any change, other than an injury, that disrupts the normal functions of the body.

3. What causes disease? • Bacteria • Viruses • Protists • Fungi • Worms • Carcinogens • Genes/Mutations

4. Pathogens • Pathogens are disease causing agents. • Diseases caused by pathogens are generally called “infectious diseases.” • Carcinogens or genetic disorders which cause disease are not pathogens.

5. The Germ Theory of Disease • Robert Koch and Louis Pasteur • Infectious diseases are caused by microorganisms commonly called germs.

6. Koch’s Postulates • Rules used to identify the microorganism that causes a disease: • The pathogen should always be found in the body of a sick organisms and should not be found in a healthy one. • The pathogen must be isolated and grown in a culture. • When the cultured (grown) pathogen is placed in a new host, the host should get the same disease. • The injected pathogen should be taken from the second host and should be found to be identical to the first one.

7. Pathogens • Viruses • Bacteria • Protists • Worms • Fungi

8. Viruses • Do not contain cells and are not classified as living. • Contain either DNA or RNA surrounded by a protein coat. • Inject DNA or RNA into the host cell and begin to replicate its DNA or RNA, taking over the functions of the host cell. • Diseases: cold, influenza (flu), smallpox, warts

9. Symptoms occur in 3-17 days. Symptoms include: High fever Backache Malaise (weakness) Vomiting Rash Small Pox

10. Bacteria • Single-celled organisms • Cause disease either by breaking down the tissues of the infected organism for food or by releasing toxins that harm the body. • Few are harmful to humans. • Examples: Streptococcus infections, diphtheria, botulism, and anthrax.

11. Swollen neck (bull neck) Soar throat High fever Vomiting Skin lesion on the leg Diphtheria

12. Protists • Disease causing protists are single-celled. • Usually transmitted (spread) by insects. • Examples: • Malaria • Caused by Plasmodium, a protist that is spread from person to person by mosquitoes. • African Sleeping Sickness • Caused by Trypanosoma, also spread by mosquitoes. • Amebic dysentery • Caused by Entamoeba caused by contaminated water supplies.

13. Worms • Flatworms and roundworms • Usually found in tropical regions of the world. • Examples: • Schistosoma: infect people working in rice fields. • Tapeworm • Hookworm

14. Fungi • Most fungi are harmless. • Athletes foot (ringworm) • Caused by Tinea • The same fungus can infect the scalp (Tinea capitis) and other areas of the body.

15. How are diseases spread? • Physical contact • Contaminated food and water • Infected animals

16. Physical Contact • Touch • Body fluids • Sneezing • Coughing • Sex

17. Contaminated Food and Water • Food poisoning (spoiled food). • Uncooked meat. • Poor sanitation and untreated sewage

18. Infected Animals • Vectors: animals that carry pathogens from person to person (mosquitoes). • Examples: Malaria, Lyme disease, West Nile Virus, and rabies.

19. Antibiotics • Antibiotics are compounds that kill bacteria without harming the cells of the human or animal hosts. • Penicillin (produced by mold): discovered by Alexander Fleming • Antibiotics have no effects on viruses.

20. Immune System • The function of the immune system is to fight infection through the production of cells that inactivate foreign substances or cells. • This process is called immunity. • The immune system includes two general categories of defense: • nonspecific defenses • specific defenses

21. Nonspecific Defenses • Nonspecific defenses include physical and chemical barriers. • First Line of Defense: skin • Very few pathogens can penetrate the layers of dead cells at the skin’s surface. • The importance of the skin as a barrier against infection becomes obvious as soon as it is broken. • Secretions of the body including mucus, saliva, and tears contain lysozyme, an enzyme that breaks down the cell walls of many bacteria. • Pathogens that enter the body through the nose or throat can be trapped by mucus and cilia (tiny hairs), which help push pathogens away from your lungs.

22. Second Line of Defense • If pathogens do enter your body, they multiply quickly, releasing toxins into your tissues. • Inflammatory response: blood vessels near the wound expand and white blood cells move from the vessels to enter the infected tissues. The infected tissue may become swollen and painful. • Fever: elevated body temperature, kills pathogens, which can usually only survive within a narrow temperature range. Elevated temperature also increases the heart rate so that WBC’s get to the site of infection faster.

23. Specific Defenses • If a pathogen is able to get past the non-specific defenses, the immune system response with specific defenses that attack the particular disease-causing agents: immune response. • A substance that triggers this response is called an antigen. • The cells of the immune system which recognize specific antigens are either B lymphocytes (B cells) or T lymphocytes (T cells). • Humoral immunity: B cells provide immunity against antigens and pathogens in body fluids. • Cell-mediated immunity: T cells provide defense against abnormal cells and pathogens inside living cells.

24. Humoral Immunity • B cells grow and divide rapidly, produce large numbers of plasma cells and memory B cells. • Plasma cell release antibodies, proteins that recognize and bind to antigens. • The antibodies are carried in the bloodstream to attack the pathogen that is causing the infection. • As the antibodies overcome the infection, the plasma cells die out and stop producing antibodies. • Once the body has been exposed to a pathogen, millions of memory B cells remain capable of producing antibodies specific to that pathogen, reducing the chance that the disease could develop a second time.

25. Cell-Meditated Immunity • The body’s primary defense against its own cells when they have become cancerous or infected by viruses. • T cells divide and differentiate into killer T cells, helper T cells, suppressor T cells, and memory T cells. • Killer T cells: track down and destroy the pathogen. • Helper T cells: produce memory T cells, act similar to memory B cells. • Suppressor T cells: release substances that shut down the killer T cells.

26. Vaccinations • A vaccination is an injection of a weakened or mild form of a pathogen to produce immunity. • Edward Jenner produced the first vaccination, using a form of smallpox which came from a cow (cowpox). • Active immunity: the type of immunity produced by the body’s reaction to a vaccine or natural exposure.

27. Immune System Disorders • 3 types of immune system disorders: • Allergies • Autoimmune disease • Immunodeficiency diseases

28. Allergies • Allergies are a common overreaction of the immune system to antigens. • Common allergies include: pollen, dust, mold, and bee stings. • When allergy causing antigens enter the body, they attach themselves to mast cells. • Mast cells are specialized immune system cells that initiate the inflammatory response. • The activated mast cells release chemicals known as histamines, which increase the flow of blood and fluids to the surrounding area. • They also increase mucus production (causing sneezing, watery eyes, runny nose, coughing, etc). • If you have allergies you have probably taken antihistamines (allegra, zyrtec, etc)

29. Autoimmune Disease • When the immune system makes a mistake and attacks the body’s own cells, it produces an autoimmune disease. • Examples: • Type I diabetes: antibodies attack insulin-producing cells of the pancreas. • Rheumatoid arthritis: antibodies attack connective tissues around the joints. • Myasthenia gravis: antibodies attack neuromuscular junctions. • Multiple Schlerosis (MS): antibodies destroy the functions of the neurons in the brain and spinal cord.

30. Immunodeficiency Diseases • AIDS (acquired immunodeficiency): results from a viral infection (HIV) that destroys helper T cells. • Discovered when patients were dieing due to what were normally non-serious infections. • They were dieing as a result of a previous infection (HIV). • As the number of helper T cells declines the normal immune response breaks down. • The progression of HIV infection can be monitored by counting the number of helper T cells. • The fewer the helper T cells the more advanced the disease.

31. Transmission of HIV (human immunodeficiency virus) • There are 4 main ways to transmit HIV: • Through any form of sexual intercourse with an infected person. • Through shared needles or syringes that are contaminated with the blood of an infected person. • Through contact with blood or blood products of an infected person. • From an infected mother to child, either during pregnancy, during birth, or during breast-feeding.

32. Is there a cure? • There is no cure or vaccine at present there is only a “cocktail” of expense medicines and vitamins allowing people to live with HIV instead of dieing from it.

33. How can you stay healthy? • Eat right. • Exercise and rest. • Abstain from harmful activities. • Get regular checkups.