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Terms in this set (46)
Viruses are nonliving infectious particles made up of viral genes enclosed in a protein capsule. They can only replicate within a host cell, which they identify with a lock and key fit between the proteins on the outside of their capsules and specific molecules on the surface of the cell. Most viruses can only infect a limited range of host cells, which means that viruses in some plants and animals are not able to infect humans. Some viruses are able to infect more than one species, such as monkey pox, SARS, and swine flu. Other viruses include common cold, flu, measles, smallpox, genital herpes, and HIV.
The body's third line of defense, the immune system, responds to specific types of pathogens that invade the body. This line of defense comes into play at the same time as the internal nonspecific defenses, and the
two lines of defense work together to protect the body. The functions of the immune system include production of specific defense proteins called antibodies as well as the participation of white blood cells called lymphocytes. A healthy immune system recognizes chemical markers on the body's own cells and proteins. These chemical markers are determined by a person's genetic coding and each individual's chemical markings are unique. This is important because it ensures that the destructive powers
of the immune system are not used against the body's own cells, only against foreign substances. When the immune system recognizes that an invader does not have the body's chemical markers, it uses cells and chemical defenses to attack them.
Molecules called antigens can be found on the outer surface of bacteria, viruses, parasites, pollen, insect venom, and transplanted tissues. When the immune system detects the antigens on the surface of the invading substance instead of the body's own
chemical markers, it triggers an immune response. Each antigen has a unique molecular shape that stimulates production of a corresponding antibody. The antibodies are specialized proteins that bind to the corresponding antigen, like fitting two puzzle pieces together. This marks the foreign substance to be destroyed by white blood cells called lymphocytes.
The white blood cells involved in the specific defenses of the immune system are primarily B lymphocytes (B cells) and T lymphocytes (T
cells). Both are produced in red bone marrow, but B cells also mature in the blood marrow while T cells mature in the thymus, an endocrine gland. The B cells and T cells are constantly patrolling the body, in search of antigens. Each type of B cell and T cell is capable of recognizing and destroying one type of antigen. B cells have embedded antibodies, so they are able to discover antigens in body fluids. T cells attack pathogens that have invaded body cells.
The specific immune response can
be divided into two main types of action: humoral immunity and cell-mediated immunity.
For a pathogen, such as a bacteria or virus, to infect your body, it must go through several lines of defense. The nonspecific defenses include the external protection of skin and mucous membranes, as well as internal defenses such as phagocytic white blood cells, inflammation, and fever. Your immune system also provides specific defenses that produce antibodies and lymphocytes that fight specific pathogens. In addition, your immune system produces memory B and T cells that allow for a much more rapid response if the same pathogen ever attacks your body again. Vaccines, medications, and antiseptics can be used to assist the immune system, as can preventative measures such as washing your hands thoroughly and avoiding contaminated food and water.
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