BIOL 100 Chapter 13/13a: Body Defenses & Infectious Diseases

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Biological Sciences
BIOL 100
Michael Webber

Chapter 13: Body Defense Mechanisms 13.1 The Body’s Defense System • common targets of the body’s defense system: • organisms that cause disease or infection • cancerous cells • pathogens-the bacteria, viruses, protozoans, fungi, parasitic worms, and prions that cause disease 13.2 Three Lines of Defense • (1) Keep the foreign organisms or molecules out of the body in the first place • chemical and physical barrier • (2) attack any foreign organism or molecule or cancer cell inside the body • internal cellular and chemical defenses • (3) destroy a specific type of foreign organism or molecule or cancer cell inside the body • adaptive immune response, which destroys specific targets 
 Innate Defenses Adaptive acquired defenses Second First Line of Line of Defense : Defense: Third Line of nonspecific defense: physical and Nonspecific immune chemical barriers internal cellular response and chemical defense If pathogens If pathogen survives penetrates nonspecific internal barriers defenses 1 o 5 • First Line of Defense: Physical and Chemical Barriers • the skin and mucous membranes • Physical Barriers • dead skin shedding and the tightness of the skin provide protection • Chemical Barriers • sweat and oil glands provide chemical barriers • Second Line of Innate Defense: Defensive Cells and Proteins, Inflammation, and Fever • Defensive Cells • phagocytes- specialized “scavenger” cells; engulf pathogens, damaged tissue, or dead cells by the process of phagocytosis • several type of phagocytes: • neutrophil- arrives at the sire of attack before the other types of white blood cells and immediately begins to consume the pathogens, especially bacteria, by phagocytosis • macrophages- created when other white blood cells (monocytes) leave the vessels of the circulatory system and enter the tissue fluids • eosinophil- a white blood cell that attacks pathogens that are too large to be consumed by phagocytosis, such as parasitic worms • Natural Killer Cells • natural killer (NK) cell-a white blood cell that roams the body in search of abnormal cells and quickly orchestrated their death • Defensive Proteins • interferons • interferons- small proteins that act to slow the spread of viruses already in the body • interfere with viral activity • mount a 2 pronged attack: • (1) they help rid the body of virus-infected cells by attracting macrophages and NK cells that destroy the infected cells immediately • (2) warn cells that are not yet infected with the virus to take protective action • help protect uninfected cells from all strains of viruses, not just the one responsible for the initial infection • complement system 2 of 5 • complement system- a group of at least 20 proteins whose activities enhance, or complement, the body’s other defense mechanisms • aka simply complement • the effects of complement include the following: • destruction of pathogens • (1) activated complement proteins form holes in the cell wall and membrane of the bacterium • (2) the bacterium can no longer maintain a constant internal environment. Water enters the cell • (3) the bacterium bursts • enhancement of phagocytosis • stimulation of inflammation • Inflammation • inflammatory response- a series of events that happen when body tissues are injured or damaged • aka inflammatory reaction • Four cardinal signs: • (1) Redness • occurs because blood vessels dilate in the damaged area, causing increased blood flow • dilation is caused by histamine • histamine- a substance released during allergic reactions and inflammation • is released by small, mobile connective tissue cells called mast cells in response to chemicals from damaged cells • (2) Heat • increased blood flow increases heat • raises the metabolic rate of the body cells in the region and speeds healing • (3) Swelling • fluid sweeps into the tissues form the bloodstream • (4) Pain • can be caused by: • excessive fluid causing pressure on nerve 3 of 5 • releasing pain-causing chemicals • pain usually prompts a person to protect the area to avoid additional injury • Fever • fever-an abnormally high body temperature • are caused by pyrogens • pyro=fire • gen=producer • pyrogens- chemicals that raise the “thermostat” in the brain to a higher set point • a (mild or moderate) fever helps the body fight bacterial infections by • slowing the growth of bacteria • stimulating body defense responses • Third Line of Defense: Adaptive Immune Response • provides the specific responses and memory needed to target invader • the immune system is an anatomical sense • its function is, recognizing and destroying specific pathogens or foreign molecules • has certain important characteristics: • (1) is directed at a particular pathogen • (2) the adaptive immune response has memory 13.3 Distinguishing Self from Nonself • MHC markers-serve as flags declaring the cell as a “friend” • aka major histocompatibility complex • the self labels on your cells are different from those of any other person • antigen-a non self substance or organism that triggers an immune response • declares a cell as “foe” • certain white blood cells, called lymphocytes, are responsible for both the specificity and the memory of the adaptive immune response • 2 types of lymphocytes: • (1) B lymphocytes • aka B cells • mature in bone marrow • (2) T lymphocytes • aka T cells • mature in the thymus gland, which overlies the heart • develop the ability to distinguish cells that belong in the body fro those that do not 4 of 5 • circulate through the body, bumping into other cells and checking to be sure those cells have the correct self (MHC) maker • both T and B lymphocytes are programmed during development to recognize one particular type of antigen • lymphocytes are prepared to respond to each antigen when it’s first encountered • when an antigen is detected, B cells and T cells bearing receptors able to respond to that particular invader are stimulated to divide repeatedly, forming 2 lines of cells: • (1) effector cells- carry out the attack on the enemy • generally love for only a few days • (2) memory cells-long-lived cells that “remember” that particular invader and mount a rapid, intense response to it if it should ever appear again • prevents you from getting ill from the same pathogen twice 13.4 Antibody-Mediated Responses and Cell-Mediated Responses • the body has 2 types of specific defenses: • (1) antibody-mediated immune respones • defend primarily against antigens found traveling freely in intercellular and other body fluids • warriors are B cells (aka plasma cells) • weapons Y-shaped proteins called antibodies, neutralize and remove potential threats from the body • (2) cell-mediated immune responses • protect against cellular pathogens or abnormal cells, including body cells that have become infected with viruses or other pathogens and cancer cells Table 13.2 Cells Involved in the Adoptive Response Cell Functions Macrophage, dendritic cell, or B cell an antigen-presenting cell: • engulfs and digests pathogen or invader • places a piece of digested antigen on its plasma membrane • presents the antigen to a helper T cell • activates the helper T cell 5 o 5 Cell Functions T Cells, helper T cell the “on” switch for both lines of immune response: • helper T cells activate B cells an dT cells Cytotoxic T cell (effector T cell) Responsible for cell-mediated immune responses: • destroys cellular targets, such as infected body cells, bacteria, and cancer cells Suppressor T cell The “off” switch for both lines of immune responses: • suppresses the activity of the B cells an dT cells after the foreign cell or molecule has been successfully destroyed B Cells Involved in antibody-mediated responses: • when activated by helper T cells, the B cell divides to form plasma cells and memory cells Plasma Cell Effector in antibody-mediated response: • secretes antibodies specific to extracellular antigens, such as toxins, bacteria, and free viruses Memory Cells Responsible for memory of immune system: • generated by B cells or any type of T cell during an immune response • enable quick and efficient response on subsequent exposure of the antigen • may live for years 13.5 Steps of the Adaptive Immune Response • Step 1: Threat • foreign cell or molecule enters the body • Step 2: Detection • macrophage detects foreign cell or molecule and engulfs it • Step 3: Alert 6 of 5 • macrophage puts antigen from the pathogen on its surface and finds the helper T cell with correct receptors for that antigen • macrophage presents antigen to the helper T cell • macrophage alerts the helper T cell that there is an invader that “looks like” the antigen • macrophage activates the helper T cell ★ the macrophage is an important type of antigen-presenting cell (APC) • Step 4: Alarm • helper T cell activates both lines of defense to fight that specific antigen • Step 5: Building specific defenses (colonial selection) • antibody-mediated defense- B cells are activated and divide for form plasma cells that secretes antibodies specific to the antigen • cell-mediated defense- T cells divide to form cytotoxic T cells, that attack cells with the specific antigen clonal selection- the process by which an adaptive immune response to a ★ specific antigen becomes amplified • Step 6: Defense • antibody-mediated defense- antibodies specific to the antigen eliminate the antigen • cell-mediated defense-cytotoxic T cells cause cells with the antigen to burst ★ plasma cells- the effector cells produced through clonal selection; secrete antibodies into the bloodstream to defend against antigens free in the blood or bound to a cell surface ★ antibodies- Y-shaped proteins that recognize a specific antigen by its shape antibodies helps defend against these pathogens in several ways that ★ can be remembered with the acronym PLAN: ★ Precipitation ★ Lysis (bursting) ★ Attraction of phagocytes Neutralization ★ ★ are also called immunoglobulins (Ig) • Step 7: Continued surveillance • memory cells formed when helper T cells, cytotoxic T cells, and B cells were activated remain to provide swift response if the antigen is detected again • Step 8: Withdrawal of forces • once the antigen has been destroyed, suppressor T cells shut down the immune response to that antigen 7 o 5 Table 13.4 Classes of Antibodies Class Structure Location Characteristics Protective Functions IgG monomer blood, lymph, and most abundant of enhances intestines all antibodies in phagocytosis; body; involved in neutralizes toxins; primary and triggers secondary immune complement responses; can system pass through placenta from mother to fetus and provides passive immune protection to fetus and newborn IgA dimer or monomer present in tears, levels decrease prevents saliva, and mucus during stress, pathogens from as well as in raising attaching to secretions of susceptibility to
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