Immune System
...nity involves the ability to recognize, respond, and remember a particular substance.” (239) The major organs of the immune system are the thymus, spleen, lymph nodes, tonsils, and bone marrow. Each of these organs contains lymphatic tissue, which consists of lymphocytes, macrophages, and other cells. The lymphocytes, which originate in the bone marrow, are carried in the bloodstream to the organs of the immune system. When the body is exposed to harmful microorganisms, the lymphocytes divide, increasing their number. The lymphocytes trigger the immune response, which causes the destruction of the microorganism. The spleen is an important part of the immune response. It is located in the left superior corner of the abdominal cavity. The spleen is composed of B and T cell, macrophages, and red blood cells, and it filters the blood in the body seeking foreign cells. The thymus is found in the superior mediastinum, and is responsible for the production of mature T cells which are then released into the bloodstream. The tonsils, found on each side of the posterior opening of the oral cavity, protect the body from harmful microorganisms entering through the nose and mouth. Lymph Nodes are found throughout the body along lymph vessels. They are responsible for filtering the body fluid. The lymph nodes drain most of the fluid in the tissue in the body. Antigens are filtered out of the lymph, which is the clear liquid found in the lymph nodes. Bone marrow is responsible for producing all the cells involved in the immune system. Each cell comes from stem cells. The stem cells mature and divide to form different cells. The cells are then released into the bloodstream and travel to the different organs that need the cells. Specific immunity results from the actions of the lymphocytes. Lymphocytes are the primary immune cells in the body. The two major types of immune cells are B and T cells. B cells are responsible for producing antibodies. Antibodies are made as a result of the immune response to remove antigens. The antibodies bind with the antigens causing the antibodies to be identified as something to eliminate from the body. The inflammatory response is stimulated by the binding of the antibodies to the antigens, and chemical mediators and other cells destroy the antigens. T cells contribute to the immune defenses in two major ways. Some help regulate workings of the immune system, while others are cytotoxic and directly contact infected cells and destroy them. First among the regulatory T cells are "helper/inducer" T cells. They are required to stimulate many immune cells, including B cells and other T cells. Cytotoxic T cells help rid the body of cells that have been infected by viruses as well as cells that have been changed by cancer. They are also responsible for the rejection of tissue and organ transplant. (“T Cells”) B and T cells are able to recognize and fight invading microorganisms. B cells are able to recognize and fight off harmful microorganisms through antibody-mediated immunity. After the first time an antigen is first exposed to the B cell, the primary response, the reaction to that antigen is different. When the antigen binds to the antigen-binding receptor on the B cell, the B cell undergoes several divisions to form memory cells and plasma cells. The plasma cells produce the antibodies. This process takes from three to fourteen days. Memory B cells are responsible for the secondary response, which occurs when the immune system is exposed to an antigen with which it has already come into contact. The secondary response takes less time to produce antibodies because the memory B cells already know how to fight the antigens. The antigen is destroyed quickly. (240) T cells are able to recognize harmful microorganisms through cell-mediated immunity. Cell-mediated immunity is most effective against microorganisms that live in the body. After an antigen activates a T cell, the T cell undergoes divisions to produce cytotoxic T cells and memory T cells. The cytotoxic T cells are responsible for the cell-mediated immune response, and the memory T cells provide a secondary response similar to that of the memory B cells. The T cells have two main effects. First they release chemical mediators that promote inflammation and phagocytosis. Second, cytotoxic T cells can come into contact with other cells and cause them to rupture. (240) Immunity occurs when the body no longer produces any disease symptoms in an individual and the body is able to resist any tissue damage as a result of harmful microorganisms. Specific immunity can be acquired in four different ways: acquired natural immunity, active artificial immunity, passive natural immunity, and passive artificial immunity. Natural immunity refers to the contact of the antigen happening in everyday life and was not intentional. Artificial immunity implies intentional exposure of an antigen or antibody in the body. Active immunity results when an individual is exposed to an antigen either naturally or artificially and the reaction of the individual’s immune system is the reason of the immunity. Passive immunity occurs when another person or animal develops immunity and the immunity is transferred to a non-immune person. Active natural immunity results from natural exposure to an antigen. Active artificial immunity is acquired through a vaccination. The antibody is introduced into the body through a shot to stimulate the immune system. Passive natural immunity results from the transfer of antibodies between a mother and her fetus. Passive artificial immunity starts with the vaccination of an animal. Then, after the animal’s immune system responds to the antigen, antibodies are removed and injected into an individual. This only provides temporary immunity since the cells are destroyed before memory cells can be made. Specific resistance develops four ways of immunity in the body to protect against harmful antigens. Sometimes the body cannot keep up with the reproductive rate of a certain bacteria or the bacteria is producing a toxin so quickly that it will cause permanent damage before the immune system can rid the body of the bacteria, then an antibiotic is required to kill the bacteria. Antibiotics are chemicals that kill bacteria cells but do not affect the cells that make up the body. The majority of antibiotics are created by certain bacteria and fungi. Antibiotics are also created synthetically. They are used to destroy bacteria that are harmful to the human body. The antibiotics can destroy the bacteria by inhibiting bacterial growth and killing bacteria directly. When taking an antibiotic, it is highly important for the individual taking the antibiotic to strictly follow the instructions. If the directions are not strictly followed, then some bacteria could still remain in the body. However, if an allergic reaction occurs as a result of the antibiotic, it should not be taken. An allergic reaction is characterized by hives, rashes, wheezing, and swellin...