Immune+System+Review+HW4+MC

1) Describe the basic characteristics of bacteria. Explain how five particular features contribute to the ability of each bacteria to cause disease. (pages 122-23). Bacteria are single celled prokaryotes, and they don’t have a nucleus. It has 3 common shapes. A bacillus has a rod shape ; a coccus has a spherical shape; and a spirillum is curved. Bacteria have a cell that contains a unique amino-disaccharide. The cell wall of some bacteria is surrounded by a capsule that has a thick, gummy consistency. Motile bacteria usually have long, very thin appendages called flagellum. They rotate 360 degrees and cause the bacterium to move backwards. Some bacteria have fimbriae, stiff fibers that allow bacteria to adhere to surfaces such as host cells. FImbriae allow a bacterium to cling to and gain access to the body. In contrast, a pilus is an elongated hollow appendage used to transfer DNA from one cell to another. Many bacteria cells also have accessory rings if DNA called plasmids. Genes that allow bacteria to be resistant to antibodies are often located in a plasmid. Growth of bacteria causes disease and also bacteria release molecules called toxins that inhibit cellular metabolism. 2) What is the structure of a virus? Is a virus living? Explain how a virus is able to reproduce. (page 123) All viruses have an outer capsid, composed of protein subunits, and a nucleic acid core, composed of either DNA or RNA, but not both. Viruses bridge the gap between the living and the nonliving. Outside a host, viruses are essentially chemicals that can be stored on a shelf. But when the opportunity arises, viruses replicate inside of cells, and during this period of time, they clearly appear to be alive. They do not live independently. A virus carries the genetic information needed to reproduce itself. A virus may also contain various enzymes that help it reproduce. A virus relies on the host’s enzymes and ribosome’s for its own reproduction. Viruses gain entry into and are specific to a particular host cell because portions of the virus adhere in a lock-and-key manner with a receptor on the host cell’s outer surface. The viral nucleic acid then enters the cell. The nucleic acid codes for the protein units in the capsid. 3) What are some ways that can explain the emergence of new viral diseases? Bird flu is passed to humans from birds. It can emerge by being transported from one location to another where it has not been before. The West Nile virus has been transported into the U.S. and taking hold in bird and mosquito populations. SARS was clearly transported from Southeast Asia to Toronto, Canada. Many viral diseases are transmitted by vectors, usually insects, that carry disease from an infected individual to a healthy individual. They can emerge because of the inability of the immune system to recognize a change in the virus that allows it to cause disease. 4) What are prions, and how do they cause disease? (page 124). They are proteinaceous infectious particles that causes a group of degenerative diseases of the nervous system, also called wasting diseases. They cause CJD in humans, scrapie in sheep, and BSE, commonly called mad cow disease. These infections are transmitted by ingestion of brain and nerve tissues from infected animals. Disease occurs when certain prion proteins change their shape into a “rogue” form that can convert normal prion proteins into the rogue configuration that does not function because it has the wrong shape. 7) How do nonspecific defenses differ from specific defense? (pages 128 and 130). Nonspecific Defenses act indiscriminately against all pathogens. Specific defenses come into play when nonspecific defenses have failed to prevent an infection. Specific defenses overcome an infection by doing away with the particular disease-causing agent that has entered the body. Specific defenses also protect us against cancer. They can be likened to special forces that can attack selected targets without harming nearby residents cells. 8) What is the first line of defense? Describe several methods of protection. (page 128). The first line of defense is barriers to entry. The inflammatory response is the second line of defense. Methods under barriers to entry include skin and Mucous membranes, chemical barriers, resident bacteria. During inflammatory response injured tissue cells and mast cells release histamine. Macrophages and dendritic cells phagocytize pathogens and release cytokines. Blood clotting walls off capillary and prevents blood loss. Neutrophils and monocytes squeeze through the capillary wall and phagocytize pathogens. 9) What is the second line of defense? Describe the various cells and chemicals and their roles in protecting the body. What are the four signs of inflammation, and what causes them? (page 129). The second line of defense is the inflammatory response. During inflammatory response injured tissue cells and mast cells release histamine. Macrophages and dendritic cells phagocytize pathogens and release cytokines. Blood clotting walls off capillary and prevents blood loss. Neutrophils and monocytes squeeze through the capillary wall and phagocytize pathogens. Chemical meditators, such as histamine, released by damaged tissue cells and mast cells, cause capillaries to dilate and become more permeable. Neutrophils call for reinforcements by secreting chemical mediators called cytokines. They attract more white blood cells to the area, including monocytes. They are long lived cells that become macrophages, which are even more powerful phagocytes than neutrophils. 10) What two types of cells are involved in providing specific defenses against pathogens? What type of immunity does each provide? (pages 130-5). The two types of cells are the B cells and the T cells. B cells produce plasma and memory cells. T cells regulate immune response and produce cytotoxic T cells and helper T cells. 11) What is the clonal selection model as it applies to B cells? What becomes of the clones that are produced? ( page 131). It states that an antigen selects, then binds to the BCR of only one type B cell and then this B cell produces multiple copies of itself; clones are made. 12) Describe the structure of an antibody. What are five main classes, where are they found, and what are their functions? ( page 132). An antibody contains two heavy long polypeptide chains and a two light short chains arranged so there are two variable regions, where a particular antigen is capable of binding with an antibody. One class is IgG which crosses the placenta from mother to fetus. It binds to pathogens, activates complement, and enhances phagocytosis by white blood cells. The next class is IgM found in circulation. It activates complement and clumps cells. Another class is IgA found in secretions wuch as saliva and milk. It prevents pathogens from attaching to epithelial cells in digestive and respiratory tract. Another class is IgD found on surface of immature B cells. Its presence signifies readiness of B cell. The last class is IgE found as antigen receptors on basophils in blood and on mast cells in tissues. Its responsible for immediate allergic response and protection against certain parasitic worms. 13) Explain how T cells recognize an antigen. What are the types of T cells, and how do they function in immunity? (page 134-35). They can’t recognize antigens without help. An antigen- presenting cell links a foreing antigen to the self protein on its plasma membrane, it carries out an important safeguard for the rest of the body. Not, the T cell to be activated can compare the antigen and self protein side by side. The activated T cell and all of the daughter cells, go on to destroy cells carrying foreign antigens, while leaving normal body cells unharmed. Cytotoxic cells kill virus-infected cells and cancer cells. Helper T cells regulate immunity. Memory T cells are ready to kill in the future. 14) How is active immunity achieved? How is passive immunity achieved? (pages 136-38). Active immunity is achieved by the individual alone producing antibodies against an antigen, being induced when a person is well so that future infections will not take place with immunizations. Passive immunity is achieved by the individual being given prepared antibodies via an injection. 16) Discuss allergies, tissue rejection, and autoimmune diseases as they relate to the immune system. ( page 138-39). Allergies are hypersensitive to substances, such as pollen, food, or animal hair, that ordinarily would do no harm to the body. The response to these antigens, called allergens, usually includes some degree of tissue damage. An immediate allergic response can occur within seconds of contact with the antigen, caused by antibodies known as IgE. Anaphylactic shock is an immediate allergic response that occurs because the allergen has entered the bloodstream. A delayed allergic response is initiated by memory T cells at the site of allergen contact in the body. Organ rejection can be controlled by carefully selecting the organ to be transplanted and administering immunosuppressive drugs. Xenotransplantation is the use of animal organs instead of human organs in transplant patients.